First-Hand:The Marine Tactical Data System and the Airborne Tactical Data System - Chapter 8 of the Story of the Naval Tactical Data System
When Commanders McNally and Svendsen wrote the NTDS Technical and Operational Requirements document, they specified two other automated systems would be developed to interoperate with NTDS. These were to be a ground based tactical data system developed by the U. S. marine Corps and an airborne tactical data system that would allow an airborne early warning aircraft to link its radar picture down to ship and ground tactical data systems using the NTDS tactical data link. Appreciating the weight and space constraints of an aircraft they stated that the airborne system would not be required to do the A Link net control function, but it was expected to perform all other CIC functions including interceptor control.
Marine Corps Air Control Before MTDS
The Marine Corps, in the mid 1950s, already had a portable ground-based aircraft command and control centers called Counter Air Operations Centers (CAOC). They were operated by Marine Air Control Squadrons (MACS). The CAOCs used World War II vintage manual radar plotting technique and relied on voice radio or phone lines to transmit air target information. They were usually equipped with a portable primary long range air search radar, two or more small ‘gapfiller’ radars, one nodding vertical scan height finding radar, and identification-friend-or-foe (IFF) sets.
The functions of the CAOC were very much like a shipboard combat information center. One or two surveillance radar operators called out air track ranges and bearings via an intercom to manual plotters who marked tracks with grease pencil dots on the back of an edge lighted transparent vertical plotting board. As in shipboard systems they wrote with mirror image writing so that air controllers seated in front of the ‘vertical situation display’ could read the glowing symbols and letters. The air controllers would occasionally ask the height finding radar operator to measure the altitude of a target, and it would be entered next to its track.
Other transparent vertical status boards were located on either side of the vertical situation display to show aircraft and airfield status and call signs, as well as missile site and gun battery status. Air controllers were situated so that they could see both the vertical situation display and their own radar scopes where they grease penciled the location of their controlled interceptor and its intended target. The controllers calculated interceptor steering vectors using vector algebra based on the interceptor-target geometry, target heading and its calculated speed. Their communication with the interceptor pilot was via UHF radio, and telephone land lines usually served to connect the CAOC with airfields and AA batteries. [Ashe, Maj. Thomas D., USMC, Ret., “Evolution of the Marine Air Command and Control System (MACCS),” Published on the Milspeak Foundation web site, www.milspeak.org]
Developing the Marine Tactical Data System
The Office of the Chief of Naval Operations authorized development of the Naval Tactical Data System, and companion airborne and Marine Corps tactical data systems in April 1956. Headquarters, Marine Corps was directed to budget for and sponsor the Marine Corp’s system, and Major Edward S. Fris (CMC Code A04C) was assigned as headquarters project officer and sponsor. His first task was to develop a set of equipment for operational testing. [Ashe]
The Bureau of Ships was responsible for all Navy electronics research and development with the exception of airborne electronics (avionics); which was the responsibility of the Bureau of Aeronautics. To serve Marine Corps electronics requirements, USMC electronics specialists staffed the Marine Corps Electronics Branch of the Bureau’s Electronics Development Division. Three sections made made up the MC Electronics Branch: Communications, Radar, and Automated Systems. Headquarters Marine Corps, in mid 1956, issued the operational requirement for an ‘automated tactical data system’ to Colonel Edwin Aitken, in charge of the MC Electronics Branch. Aitken gave the operational requirement to his head of the Automated Systems Section, Major Donald F. Mileson. [Sudhoff, Capt. Richard I., USMC, Ret, Interview with D. L. Boslaugh, 17 Aug. 1994]
Mileson knew that the basis of his new operational requirement was the McNally/Svendsen NTDS Technical and Operational Requirements document, and since the two commanders were right there in BUSHIPS and also in the Electronics Division, his first act was to get their thoughts on his new development assignment; which he decided to call the Marine Corps Data System MCDS). Maj. Mileson then dissected the operational requirement into a table of system capabilities; each of which could be measured, and further described in terms of specific equipment types. Required system capabilities included: 1. a situation display showing airfield locations, participating MCDS unit locations, gun & missile batteries location and status, and the location and status of all airplanes in the defended area, 2. threat evaluation of unidentified and hostile air targets, and recommendations for assigning high threat aircraft to appropriate AA batteries or interceptors, 3. an automatic radio data link with participating NTDS and airborne early warning units, 4. automatic data links with AA batteries, and 5. automatic data links with interceptors having data link terminals. [Bureau of Ships, Contract Specification, Marine Corps Data System, SHIPS-M-2671, 13 Feb. 1957]
Major Mileson envisioned two levels of automated Marine air control facilities. A squadron level air control facility would be used by Marine air control squadrons and be called a Tactical Air Operations Center (TAOC). The TAOC would have functions similar to a shipboard combat information center including: processing air target positions from search and height finding radars, doing threat evaluations of unidentified and hostile aircraft, transmitting engagement and firing orders to local AA gun and missile batteries, and controlling assigned interceptor aircraft.
The second type of Marine air command and control center would serve the air wing or headquarters squadron level, and would have a number of squadron level Tactical Air Operations Centers under its jurisdiction - usually three. It would be called a Tactical Air Command Center (TACC) and have responsibility for Marine air operations over a wide area. Tactical Air Operations Centers would be tied to other TAOCs, air fields, AA batteries and with the higher level Tactical Air Command Center with a combination of voice lines and a digital Inter Center Data Link (ICDL).
[Obenhaus, Col. L. E., USMC, “Marine Air Command and Control Modernization,” U. S. Naval Institute Proceedings, Vol. 112/12/1006, Dec. 1986, p. 98] [Ashe]
Both levels of centers were to be equipped with standardized, building block, portable helicopter huts containing data processing, display, communications, power generation, command and decision making, and maintenance facilities. Their contents and layout was to be designed to keep the amount of inter-hut cabling to a minimum. Each Tactical Air Operations Center or Tactical Air Command Center was to be made up of as many huts of each type as its operational mission called for. None of the helicopter huts could weigh more than 2,500 pounds. This weight constraint would sometimes come into serious conflict with the requirement to minimize number and length of inter-hut cables. [Ashe] [Armed Forces Management, “For the Sea-Going Services, The Naval and Marine Tactical Data Systems are ‘The Best Since Radar’,” Armed Forces Management magazine, July 1966, p. 81]
Maj. Mileson next tasked the Naval Research Laboratory in Washington, D. C. to prepare a specification for an industry study contract to further define the Marine Corps Data System. This step marked a radical change from the way the USMC had acquired most of its equipment and systems in the past. Except for amphibious assault vehicles, the Marines had bought items developed by the other services. For example they bought aircraft developed by the Navy, Army artillery and tanks, and search radars developed by the U. S. Air Force. This change would cause some problems at the congressional funds authorization level due to lobbying by the Air Force who felt that developing portable air command and control systems was their prerogative. [Ashe]
The winner of Mileson’s request for proposals was a Beverly Hills, California, subsidiary of Litton Systems, Inc., called the Data Systems Division. BUSHIPS issued the study contract to the Data Systems Division in June 1957. Later that year, Headquarters, Marine Corps changed the name of the development to ‘Marine Tactical Data System’ to achieve better consistency with the names of the Airborne Tactical Data System and the Naval Tactical Data System. [Gebhard, Louis A., Evolution of Naval Radio Electronics and Contributions of the Naval Research Laboratory, NRL Report 7600, Naval Research Laboratory, Washington, D. C.,Jan 1976, p 392] [Sudhoff, Capt Richard I., USMC, Propagation Study to Support the Communication Requirements of the Marine Tactical Data System, Thesis, Naval Postgraduate School, Monterey, CA, 1958, pp. 5-6]
Litton’s first idea for communications among MTDS operational centers, command centers, and controlled AA batteries was to use the NTDS tactical data (A) link. When they explored the idea in detail, however, they found that a group of USMC activities communicating among themselves as well as communicating with NTDS and ATDS participating units over the same common data link would probably overload the link, resulting in slow response times for all participants. Litton also questioned whether NTDS high frequency data transmission would work with the required gapless coverage over the rough land areas that MTDS units might have to operate in. Even though NTDS HF radios got a solid 300 mile gapless ground wave coverage over the ocean, things could be much different in mountainous terrain, and the Marine operational requirement called for at least 100 mile gapless coverage even in mountainous terrain. Litton needed to experiment and study the communications question further before they could pick a landward data link communications medium. [Sudhoff, pp. 6-14]
It was November 1957 and Capt. Richard I. Sudhoff, USMC, was in his third year at the U. S. Naval Postgraduate School. Monterey, California, working toward a master’s degree in communications electronics. At the time he was searching for an appropriate master’s thesis topic, and his faculty advisor, Professor Mitchell Cotton, happened to mention that Litton Industries had just been awarded a Marine Tactical Data System study contract, and that they would soon start a study to determine the best approach for the landward communications link. Sudhoff thought it would be an excellent subject for his thesis if he could get involved in that study. And, there was a way to do just that. The Postgraduate School required master’s students in engineering to work for one semester in an industrial research laboratory or engineering project in the subject area of their thesis. It was up to the student to pick the company and make the arrangements.
Sudhoff found that the MTDS project head at Litton was Mr. Howard P. Gates, and he quickly got a letter off to Gates explaining the PG School industrial tour program, and his desire to work on a Marine Corps communication problem. Gates was delighted, and in early 1958 Sudhoff arrived at Litton After a few months of study, Sudhoff confirmed that using the NTDS A Link for landward communication was not a good idea. He recommended that MTDS should use the A Link only for communicating with NTDS participating units, and that a separate data link, using a different communications media than HF radio should be used for landward communication. He proposed that communications with NTDS units should be via a helicopter hut-housed relay installation equipped with NTDS A Link equipment and the equipment needed to translate between A Link formats and whatever formats the landward link would use. The relay installation would be located at the Tactical Air Command Center level, and for it he coined the name “Beach Relay.’
The next question was to determine the best radio transmission medium for the Marine’s landward data link communications requirements, and it had to be solid, out to at least 100 miles, even in mountainous terrain. Sudhoff’s study specialty was radio propagation and he had already done a lot of reading in the area, and he had noted a new media that might fill the bill for gapless communication. It was a fairly new and untried technology and it depended on the ability to build extremely sensitive radio receivers in the UHF range. It was called tropospheric scattering, a phenomena caused by turbulent air in the tropospheric layer of the atmosphere, just below the stratosphere. The turbulence scatters a little bit of radiated UHF energy downward, even though the majority of UHF radiation is line-of sight, and is not reflected back to the earth by the ionospheric layer as i s HF radiation. He had read that the new medium had worked well in experiments, and he proposed that MTDS should investigate ‘troposcatter’ for landward communications. [Sudhoff, Capt. Richard I., USMC, Ret, Letter to D. L. Boslaugh, 19 Sept. 1994] [Sudhoff, p.91]
Marine Corps policy called for officers who had received an engineering master’s degree at USMC expense to serve at least one tour in a billet where they would put that degree to use. It was called a ‘payback tour,’ and Sudhoff found himself ordered to his first payback tour upon graduation from USNPGS. He was to report to the Marine Corps Electronics Branch in the Bureau of Ships and he was going to work on the MTDS project. Thanks to his thesis study, Sudhoff was put to work on both the landward and the seaward communications systems. Because seaward communication was going to use the NTDS A Link, Sudhoff became the Marine Tactical Data System representative on the Tactical International Data Exchange Committee (TIDE). Here he worked with Lcdr. Edmund Mahinske of the NTDS project office and Leo M. Puckett representing the Airborne Tactical Data System. Sudhoff recalls that although the three USN project representatives often argued violently among themselves about data link features and standards, they always presented a solid, unified U. S. Navy front when meeting with their Royal Navy and Royal Canadian Navy counterparts. During his first couple of years in the project office when Sudhoff wasn’t working on data link standards he spent his time working with Maj. Mileson writing detailed system and equipment specifications based on input from Marine air control specialists, discussions with the NTDS project officers and the Litton study contract. [Sudhoff letter]
Each tactical air center (TACC or TAOC) had to be able to take input from four radars simultaneously, usually one long range two-dimensional, one three dimensional, and two gapfiller radars. All radars were mobile and transportable by helicopter. Each center was to be able to run 20 simultaneous air intercepts and track a maximum of 250 air targets. In addition to the challenges inherent in the new technologies of digital equipment and transistors, the helicopter transportable huts were also a considerable challenge. Among other things, they had to devise a special universal sling for suspending the huts below a number of helicopter types. Furthermore, the various helicopter types had different lifting capacity, and the huts could not weigh more than the lifting capacity of the least capable. This weight limit was set at 2,500 pounds per hut. Thus, weight control was always on their mind, and the project became very adept at helo hut weight control. They eventually became so skilled in this area that the Air Force asked the MTDS project to develop a version of MTDS for USAF use as an air transportable air defense command and control center. [O’Connell, Maj. William J., USMC, “Marine GCI- Past Present and Future,” Published on GlobalSecurity.org web site] [Armed Forces Management, p. 81] [Meyers, Robert A., Letter to D. L. Boslaugh 18 Jan 1995] [Ashe]
The MTDS electronics shelters not only had to be transportable by helicopter, but also had to be transported by many other means to just about any place in the world. Transportation could include ships, trains, trucks, and cargo airplanes. It was not uncommon to be dropped by a few feet from a helicopter. They had to operate in temperature extremes ranging from the desert to the arctic, and in extremely humid jungle environments where they would be exposed to not only high humidity but also mildew, mold, and jungle fungus. In the desert they had to survive high velocity sand storms. They had a set of environmental testing requirements every bit as severe as shipboard electronic equipment, and some of them were very unusual. For example, there was the railroad box car test and the dreaded Munson road handling test. [Armed Forces Management, p. 78, p. 81]
In late 1959 the Bureau of Ships authorized Litton Industries to begin developing an engineering test MTDS system. Enough prototype equipment and helo huts were to be provided to equip one Tactical Air Command Center (designated AN/TYQ-1) and two Tactical Air Operations Centers (designated AN/TYQ-2). One beach relay (designated AN/TYQ-3) was also to be provided to operate with the Tactical Air Command Center.
Litton elected to use a drum-memory based computer of their own design in the TAOCs and the TACC, however they decided to use a modified NTDS unit computer in the beach relay system in order to ensure compatibility with the NTDS A-Link. The task to Litton also included developing the MTDS display subsystem, and writing the computer programs for the two types of tactical air centers and the beach relay.
The shipboard NTDS unit computers were water cooled so the primary change needed to the CP-642 computer was changing it to work with the air cooling systems used in the MTDS beach relay huts. In mid 1960 the NTDS project office diverted one unit computer from the Univac production line to be delivered to Litton for modification to air cooling. The MTDS project office in December 1961 contracted with the maker of the NTDS A-Link equipment, Collins Radio, to develop a prototype beach relay. It was to be housed in three helo huts, and it was envisioned it would work only with the Tactical Air Command Center which would communicate with participating NTDS units. [Rockwell International Corporation, Commerce Bulletin Daily Synopsis No. 310, Contractor Qualification for Development and Integration of a New Link 11 System for use with the Navy Tactical Data System, undated, estimated year 1975]
Testing the Prototype MTDS
The Marine Corps Air Facility, Santa Ana, California, was conveniently close to Litton Data Systems, and not too far from the ground based NTDS installation at the Fleet Anti Air Warfare Training Center (FAAWTC), San Diego. It was a logical place to test the prototype MTDS. The Marine Third Air Wing operated from the Santa Anna Facility, and was supported by Marine Air Control Squadron-3 (MACS-3). In early 1961 MACS-3 was detached from the Air Wing, placed under administrative control of Fleet Marine Forces, Pacific, and designated as the the Marine Tactical Data System testing unit. LtCol. Edward S. Fris, who had been the original sponsor of the MTDS project while he was at Headquarters. Marine Corps, had served in a subsequent tour as the Marine Corps Representative at the Litton Data Systems plant where MTDS was developed, and had then then ordered to take command of MACS-3 to oversee all of the testing required to determine the operational suitability and maintainability of MTDS. [Ashe]
In September 1961 Litton began delivery of equipment to make up three prototype MTDS sub units; one Tactical Air Command Central (TACC)to be located at MCAF Santa Anna, one Tactical Air Operations Central (TAOC) also located at Santa Anna, and one TAOC to be located at Marine Corps Base, Twenty Nine Palms, CA. Collins Radio also delivered one Beach Relay facility to be used by the Air Command Central to communicate with NTDS participating units, in particular with FAAWTC, San Diego. The testers were charged with finding if the three units could develop a comprehensive tactical air picture based on inputs from USMC air search radars and IFF equipment, if the system could effectively perform threat evaluation and weapons assignment recommendations based on the air picture, if it could effectively control interceptor aircraft by voice radio and automatic interceptor control data links, and if it could effectively trade target and assignment data with NTDS units. The TAOC at Twenty Nine Palms was connected by the Inter Center Data Link to Marine surface to air missile batteries to determine the ability of MTDS to control the batteries. [Ashe]
MACS-3 was also charged with conducting a number of field environmental test on the helo huts which passed both the boxcar handling and the Munson road handling tests. This was in spite of severe damage to the truck carrying the huts in the Munson test. [Armed Forces Management, p. 78] As in the engineering test Naval Tactical Data System, the MTDS operating shelters were equipped with a number of types of operator consoles, but the testers found the number of different types caused logistics and maintenance problems. They recommended that one one universal console type be developed to be used in a universal operator’s hut that could be used interchangeably for air tracking and identification, air traffic control, interceptor control, or weapons assignment and command functions. They recommended three of the universal displays be installed in each hut. [Naval Ship Systems Command, NTDS/MTDS/ATDS Collins Activity Report 1955-1970, 5 March 1970] Testing continued throughout 1962 and into 1963, when USMC Headquarters authorized production.
In late 1964 MACS-3 was given another testing assignment when the new Airborne Tactical Data System, installed aboard the first E-2A ‘Hawkeye’ airborne early warning airplanes, started fleet testing. This time the unit participated in operational suitability testing with ATDS and NTDS units to demonstrate that the three sea service tactical data systems could function as one system. [Bureau of Ships,Technical Development Plan for the Naval Tactical Data System (NTDS)-SS 191, 1 Apr. 1964, p. 2-2, p.4-7]
It had been assumed at the start of MTDS development that the working level unit of the system, the Tactical Air Operations Central would always be deployed reporting to a higher level Tactical Air Command Central, usually with a ratio of three TAOCs to one TACC. And, that the TACC would be the point at which the system would communicate with NTDS and ATDS units via a Beach Relay. During testing, however, it was realized that the air operations centrals would often be deployed by themselves without a higher level command central, and that the operations centrals would need the ability to interface directly with the Beach Relay. Accordingly, the operations central and the Beach Relay designs were reworked so that the TAOC could also be equipped with the capability to communicate on the NTDS A Link. In the process the new Beach Relay subsystem was redesignated a Tactical Data Communications Central (TDCC), AN/TYQ-3, and it had the capability to communicate either with a TAOC or TACC. [Ashe]
The MTDS project office and headquarters sponsor also accepted the recommendation for a universal operator’s console. All consoles were to be able to display raw radar video, IFF video, and overlaid with computer generated graphics, whereas the prototype weapons control and command function consoles had been given only computer generated displays without raw video or IFF beacon returns. The prototype consoles had used a light pen for operator interface but the light pen had been found maintenance intensive and hard to use during testing, and it was decided the production consoles would use a touch sensitive display. Normally an air operations central would be equipped with five universal operator shelters having a total of 15 consoles. [Ashe]
For production HQMC elected to buy equipment only to equip the lower level Tactical Air Control Centrals, and production was authorized for 14 AN/TYQ-2 equipment suites to support three Marine Air Control Squadrons at each of the three active Marine Air Wings plus suites for operator & maintenance training, and battle damage replacement. Two unsheltered TYQ-2 suites were also authorized for the Marine Corps Communications Electronics School at Twenty Nine Palms, CA. [Ashe] HQMC authorized production contract awards to Litton and Collins Radio in mid 1964.
Production had hardly started when the project ran into a snag. A senior Department of Defense acquisition review official, who had just entered the DOD from the computer industry, could not believe it when he saw that MTDS was going to use what he considered to be an outdated magnetic drum based computer rather than more modern magnetic core memory. He was concerned with the predicted relatively low reliability of mechanical memory drums compared with the ‘much higher’ reliability of magnetic cores, and gave the Marines a choice of switching to a core memory computer or proving that Litton’s drum machine met USMC reliability requirements. The project was put on hold for months of drum reliability testing, but the project proved that the computer met their field reliability requirement, and they were allowed to continue. With production assured, future MTDS operators and maintainers were assigned for training at the Marine Corps Communications Electronics School, and the Tactical Data Communications Central (old Beach Relay) maintainers were assigned to training at the Univac plant at ST. Paul, MN, where the TDCC systems were being mated with the modified air cooled NTDS unit computers. [Meyers, Robert A, letter]
Marine Air Control Squadron-3, the MTDS testing unit, was the first to receive a production AN/TYQ-2 in March 1966 suite to verify that the changes worked. Upon verification, the next suite, an unsheltered set, went to the operator and maintenance training school at Twenty Nine Palms. Then in September 1966 the first operational suite was delivered to MACS-4 at Camp Pendelton, CA. They were also to be equipped with the new AN/TPS-34 auto detecting three dimensional radar. MACS-4 immediately put the new system to work, and though they had expected improvements over the manual plotting routine, it greatly exceeded their expectations. Marine Air Control Squadron-7, an old style manual plotting unit, was already in combat based at Da Nang, South Vietnam, and MACS-4 was scheduled to relieve them in June 1967; then MACS-7 would return to Camp Pendelton to get their new equipment. [Ashe] [O’Connell]
Concurrently with the delivery of MTDS to the Fleet Marine Force, the BUSHIPS Marine Corps Electronics Branch fielded a new three dimensional, long range air search radar, the transportable AN/TPS-34. This radar automatically measured the range, bearing, and altitude of all aircraft within its search envelope and provided it to operator consoles without requiring a height request. For the first time, the MACS could have a complete, constantly updated air target picture in three dimensions. [Ashe]
The Troposcatter Communications System
We have read in an earlier section Major Richard Sudhoff of the MTDS project office had championed a troposcatter communications system as the medium for tying together MTDS units, as well as tying them to the Beach Relay system. After three years of persistence with his HQMC sponsors Sudhoff finally won. In early 1962 they authorized the project. Sudhoff was slated to detach from the project office in September for a tour on Okinawa, but he had time to draft detailed procurement specifications, get their approval, and turn them over to his relief, Major Bill Murray. Radio Corporation of America won Murray’s competitive request for proposals and built a prototype troposcatter system designated AN/TRC-97. The Marine Corps Development and Test Center at Quantico, VA, took delivery of the prototype and completed a successful evaluation in June 1967.
Upon authorization for production, the TRC-97 was designated not only the communications medium within MTDS units, the Beach Relays, and with their Hawk missile batteries, but also it was adopted generally across the Marine Corps and Air Force units as a mainstay overland communications medium for voice, teletype and data link transmissions. [Sudhoff, LtCol. Richard I., USMC, Letter to D. L. Boslaugh 19 Sept. 1994]
The Marine Tactical Data System in Viet Nam
On Monkey Mountain
On a Saturday night in May 1965 Marine Air Control Squadron-7, based in Atsugi, Japan, received urgent message orders to send mobile radar equipment and a team of radar operators to set up a radar site at Phu Bai, South Vietnam, just southeast of the city of Hue. Their purpose would be to provide early warning air contact information to the Air Force’s ‘Panama’ radar installation located a few miles east of the city of Da Nang on Monkey Mountain. By the evening of the next day the Marines had airlifted men and equipment to the new site, and it was in operation.
The remaining personnel and equipment of MACS-7 was relocated in mid 1965 to support Marine Air Wing I operations and were based near the airport at Chu Lai, South Vietnam, where they set up a World War II style manual plotting Counter Air Operations Center. Here they received air target position inputs from the Phu Bai radar site and other Marine Corps radars by voice transmission over telephone land lines and radio circuits. Air target track summaries were plotted by hand on large vertical edge lighted plexiglass boards having spider web-like polar coordinate grids printed on them. From the information on the vertical summary plots, and many status boards showing the status of interceptors and AA batteries under their control, the Marine air controllers directed interceptors, sent orders to AA batteries, conducted general air traffic control, directed flying tankers to refuel thirsty aircraft, and rendered aid and directions to friendly airplanes in their area. MACS-7 would continue this operation for the next two years. [McCutcheon, LtGen Keith B., USMC, “Marine Aviation in Vietnam -1962-1970,”U. S. Naval Institute Proceedings, Vol. 97, N0. 819, May 1971, p. 138]
MACS 4 was to relieve MACS 7 but its CO was told that they would not necessarily be located at the MACS-7 Chu Lai site, but rather should find a site that best suited the capabilities of their new system. In November 1966 a survey team from MACS-4 arrived in Vietnam to select an operating site for their new TAOC. The team looked at sites in the areas of Phu Bai, Da Nang, Chu Lai, and Ky Ha, keeping in mind that their responsibility would cover the Northern I Corps area and that they would be supporting aircraft returning to the Chu Lai and Da Nang airfields after strikes on North Vietnamese targets. Also they needed a good location from which to communicate over the NTDS A-Link with NTDS ships in the Gulf of Tonkin. The location that best met these requirements was the center peak of Hill 647, better known as Monkey Mountain, on a peninsula rising out of the ocean just east of Da Nang. There, radars would have a commanding view of the airspace over the northern operating area as well as a clear seawards communication path for the A link. They would be near the USMC Monkey Mountain Hawk AA missile battery, and only a mile from the USAF Panama radar site. They would be tied by automatic data link with not only the local missile battery but also with Hawk batteries at Da Nang, Hai Vin Pass, and Chu Lai. [Ashe]
In the world of inter service politics, the Air Force took a dim view of the Marines being the first to field an automated ground based air command and control system; and in an area that they felt was their purview. The USAF proposed instead that the MACS-4 MTDS equipment should be turned over to them and operated by Air Force personnel. In remembrance of the effort the Air Force had put in to derail the MTDS project and divert the funds to a USAF development, there was some laughing at Headquarters USMC, and the response that if MTDS was going to Vietnam, it would be operated by Marines. [Ashe]
In early 1967 an advance contingent from MACS-4 flew to Da Nang to coordinate Monkey Mountain site preparation with Marine Air Wing I. Navy Seabees first built a road up to the center peak of Hill 647 and flattened off its top. Then they began site preparation, including blast wall protection for the equipment shelters. All MACS-4 MTDS equipment, and radars, except the Tactical Data Communications Central (Beach Relay) as well as squadron personnel were loaded aboard a Vietnam-bound ship that arrived at Da Nang in early June 1967. The TDCC was still in test and would be shipped by air later. Offloading of the 16 MTDS equipment shelters & radars was done at the Tien Sha Naval Support Activity and trucked to the Monkey Mountain site. The four TDCC shelters arrived by air soon after the initial shelters were in place.
The MACS-4 Tactical Air Operations Center was connected with Marine Air Traffic Control Units at each USMC air base by troposcatter radio links so that Marine aircraft could be handed off between the TAOC, that did en-route air traffic control, and the local traffic control units that did approach and landing control. The MACS-4 TAOC went operational in July 1967, and MACS-7 ceased operations to return to Camp Pendelton and receive its new MTDS equipment. [McCutcheon, p. 138] [Ashe]
The Southeast Asia Interface
Air Force, Navy, and Marine Corps aircraft all participated in air strikes against North Vietnam as well as in tactical attack missions in support allied troops on the ground, and it was necessary that the air missions be well coordinated and that each service knew where the other service’s aircraft were and what they were doing. Navy and Marine Corps aircraft could operate as one unified force because of the tie between MTDS and NTDS by way of the NTDS A-Link (by then called NATO Link 11). However, there was no automated tie between Marine Corps/Navy and the Air Force, even though the Air Force did have a computerized radar system that had surveillance radars and command centers linked together in an area that covered almost all of Vietnam, Laos and Thailand. One of the Air Force radar sites, code named Panama, was located on the western peak of Monkey Mountain only about a mile away from the MACS-4 site. In order to get some sort of data exchange between the Air Force system and NTDS/MTDS, the Air Force would send operators over to MACS-4 where they would man a surveillance console and pass MTDS/NTDS air track information to the Air Force system by telephone. Air Force operators could then enter the track information into the automated USAF system, and could also send their track information to their operator at MACS-4 who could enter it into MTDS/NTDS. [Ashe]
This data interchange by way of human operators was at best slow and cumbersome and it was realized that it must be automated as soon as possible. There were at least two technical problems: 1. the NTDS/MTDS data link was the 30-bit parallel whereas the USAF data link was high speed serial, and 2. the data formats were totally different. The stakes were high. If a fast automated tie could be made between the two systems, one complete air surveillance and status picture could be achieved showing all air activity in the South China Sea, Tonkin Gulf, North and South Vietnam, Laos and Thailand. Furthermore the USAF and USMC air surveillance sites on Monkey Mountain were the obvious place to link the systems together. [Ashe] [McCutcheon, p. 138]
Once advised of the possibility, the Joint Chiefs of Staff issued a directive to make the automated linkup as soon as possible, and they directed setting up a joint service group to work on the details. The working group soon had the details worked out, and proposed a new helicopter transportable shelter that would contain the electronics needed to translate between the parallel and serial transmission formats. They also recommended that the conversion of the actual data formats be done in the Marine’s CP-808 Tactical Data Communications Central (Beach Relay) computer. In their concept, the Marine’s computer would appear to the Air Force System as another USAF radar site. The Beach Relay would broadcast Air Force track information on Link 11, and in turn, would send the complete MTDS/NTDS air situation picture to the Air Force system.
The JCS authorized a quick reaction project, code named ‘Iron Horse’ to build the interconnect, and assigned the NTDS project office in the Bureau of Ships as lead developing agent. BUSHIPS, in turn, tasked the Navy Electronics Laboratory at San Diego to design the system, build the equipment, and install it in an MTDS helicopter hut. At the same time MTDS computer programmers wrote the computer program that would translate between the two data formats. The new helicopter hut was outfitted by July 1967 and ready to participate in testing the modified computer program. Later that summer the Iron Horse hut was in operation atop Monkey Mountain, and the Air Force command center in Thailand was able to view the entire air picture in Vietnam, the Gulf of Tonkin, and the South China Sea, whereas the task group commander in the Gulf of Tonkin could view the complete air picture as far to the west as Thailand, thanks to the MTDS Beach Relay. [McCutcheon, p. 138]
Lieutenant Colonel William A. Cohn had been commanding officer of Marine Air Control Squadron-4 since its arrival in Vietnam. After the system had been in operation for about one year, he wrote a letter to Mr. Gordon Murphy of Litton Systems, Inc., the builder of MTDS. In the letter he related that since the system had gone on-line in June 1967, it had run for over 8000 hours of continuous operation, and there had been only two hours during that time when the system could not perform all its functions. During the month of March 1968, for example, MACS-4 had given assistance to 14,000 aircraft of the Air Force, Marine Corps and Navy, in the same period his air controllers had coached several airplanes to safety or directed emergency refuellings. This possibly saved a number of pilots lives or prevented their falling into captivity. On top of that, during the past 11 months his personnel had run 1100 live intercepts. He emphasized that they could not have done these things without MTDS, and that the pilots had high praise for the help of the squadron and for the Marine Tactical Data System. [Cohn, LtCol. William A., USMC, Letter to Mr. Gordon Murphy if Litton Industries, Inc., 14 May 1968]
The reader may remember that LtCol Richard I. Sudhoff, when in the MTDS project office, had championed a troposcatter communications system to tie the elements of the Marine Tactical Data System, its radars and missile batteries together. It was eventually fielded with the designation AN/TRC-97 and the marines in Vietnam used it not only in MTDS but also as a general overland communication link among USMC units. Sudhoff was told by marine friends that the TRC-97 turned out to be robust and versatile. For example during the Viet Cong siege of Khe Sanh, the Marine defenders found that the murderous crossfire raised havoc with their exposed TRC-97 antenna and it was destroyed over and over again. They solved the problem by removing the antenna feed horns and fastening them in five gallon coffee cans. They put the cans on top of their communications bunker, pointed the open ends toward their headquarters, and achieved solid communication over a 50 mile path. [Sudhoff, LtCol. Richard I, USMC, Letter to D. L. Boslaugh, 19 Sept. 1994]
The Amphibious Force Flagships
In the days of sailing ships, men of war carried a detachment of Marines who’s function in a sea battle was to climb high in the rigging and fire down on the decks of opposing ships. Their specialty was spotting enemy officers and doing them in, as exemplified by the French Marine who’s bullet ended the life of Lord Admiral Nelson at the Battle of Trafalgar. The Marine’s other specialty was amphibious landings, which over the years progressed from rowing ashore in a ship’s boat to the massive amphibious landings of World War II.
One only has to think of the Normandy Invasion to form an idea of the complexity of a modern amphibious landing. First, extensive intelligence gathering and planning is needed. Next, enemy hardpoints have to be softened up by bombing and naval gunfire. Then, underwater mines and beach obstacles must be cleared, the latter by highly trained teams of demolition experts who often must sneak to the beach under cover ahead of the invasion forces. Then the right mixes of infantry, protecting armor, and artillery must be transported ashore to the right locations and in precise sequences. After that comes a massive logistics and supply operation to sustain the forces ashore. The WW II amphibious force flagships had generally been converted merchant ships, but in 1962 Navy planners began working on the concept of a new ship class designed from the keel up for the command and control of amphibious forces.
The amphibious force sponsors had been watching the progress of the Naval Tactical Data System project with interest and asked the Bureau of Ships if NTDS equipment could be put to use in their new flagships. After reviewing the multitudinous functions of amphibious assault command and control the NTDS project stated that the standard NTDS equipment, augmented by developing new militarized line printers, computer driven plotters and rotating disk mass memories, could do the job. The new equipment would be needed to automate the clerical, data storage and data retrieval requirements of the amphibious and intelligence support systems. Miller, Cdr. A. S., USN, “USS Mount Whitney (LCC-200,” U. S. Naval Institute Proceedings, Vol 103/11/897, Nov. 1977 pp. 107-108] [Naval Ship Systems Command, Letter to Commander Puget Sound Naval Shipyard, Commander Philadelphia Naval Shipyard, Subject: AGC-19/20 Command and Surveillance System Test Development Directors: assignment of, Serial 9670 Ser 6172B- 65, 26 July 1967]
In 1964 Congress authorized the construction of two new special purpose amphibious force flagships, AGC 19 and 20, to be named Blue Ridge and Mount Whitney. The ships would have to be equipped to support not only a landing force commander, but also the afloat amphibious task force commander. As compared with their predecessor AGCs, the two ships would have considerable more communications facilities and would have the largest NTDS installations afloat. Each ship would have eight separate automated command support centers, and each center would have about the same amount of NTDS equipment as a guided missile frigate. [Moore, Capt. John, RN, Editor, Jane’s American Fighting Ships of the 20th Century, Mallard Press, New York, 1991, ISBN 0-7924-5626-2, p. 249]
Philadelphia Naval Shipyard launched Blue Ridge in January 1969 and Newport News Shipbuilding launched Mount Whitney a year later. During the ships’ construction the Navy changed their designation from amphibious force flagship to amphibious command ship; changing the AGC to LCC. Blue Ridge was commissioned on 14 Nov. 1970, and Mount Whitney on 16 Jan 1971. [Moore, p 249] The two ships fulfilled their amphibious command role admirably, perhaps too well, for they periodically carried an embarked fleet commander who used their extensive communications and data processing installations in fleet command support. The fleet commanders really liked the capabilities the two ship’s systems gave them, and in 1979 convinced the Chief of Naval Operations that the two LCCs should be turned over to the Commanders of Second and Seventh Fleet for their exclusive use. [Gatchel, Col. Theodore L., USMC, “TAD for the LCCs?,” U. S. Naval Institute Proceedings, Vol. 108/11/957, Nov. 1982, p. 111]
With the reassignment of the LCCs, the Marines and amphibious force commanders were not completely left out in the cold, nor did it mean the end of using NTDS in amphibious command support, for a new class of general purpose amphibious assault ships was already serving the fleet. The first of this new class, USS Tarawa (LHA 1) had been launched in December 1973, and it had much the same extensive NTDS amphibious command support facilities as the LCCs. Four more of these helicopter landing assault carriers would join the fleet. [Navy Department, Office of the Chief of Naval Operations, Naval History Division, Dictionary of American Naval Fighting Ships-Volumes I-IIIV, United States Government Printing Office, Washington, D.C. 1964-1981, Vol VII, p 47]
As of the year 2011 USS Blue Ridge still serves as the command ship of the U. S. Seventh Fleet, home ported in Yokosuka, Japan where she provides command, control, communications, computers, and intelligence support for the fleet commander and staff. From August 1990 to April 1991 Blue Ridge served as flagship for U. S. Naval Forces Central Command during operations Desert Shield and Desert Storm, and later was one ot the USN ships providing disaster relief to Japan following the 2011 earthquake and tsunami. In this role she carried relief supplies from Singapore to Japan. USS Mount Whitney is presently Sixth Fleet flagship and at the same time command and control ship for Commander, Joint Command Lisbon and Commander, Striking Force, NATO. As of March 19 2011, the ship was the main command ship for enforcing United Nations Security Council Resolution 1973 pertaining to the protection of Libyan citizens during the Libyan rebellion against Muammar Gaddafi. Both ships are expected to remain in service until 2039, a 69 year life span!. [USS Blue Ridge (LCC-19), From Wikipedia, the free encyclopedia] [USS Mount Whitney (LCC-20), From Wikipedia, the free encyclopedia]
The Airborne Tactical Data System
Evolution of Airborne Early Warning in the U.S. Navy
The reader may recall that in addition to the Marine Tactical Data System the McNally/Svendsen NTDS Technical and Operational Requirements paper called for an airborne version of NTDS to enable an airborne early warning (AEW) airplane to participate on the tactical data link so that it could link its radar picture down to NTDS and MTDS participating units, and vice versa.The idea of a radar equipped airborne early warning aircraft was not new. They had been extending the eyes of the fleet since the end of World War II. The first use of AEW airplanes was intended to detect low flying Kamikaze attacks that shipboard radars could not pick up until they were uncomfortably close to their intended victim.
To counter the low flying menace, in 1945 twenty seven Grumman Avenger torpedo bombers were stripped of weapons and armor and were fitted with AN/APS-20 microwave radars. The APS-20 had been developed by the Radiation Laboratory of the Massachusetts Institute of Technology from 1942 to 1945. It featured a large rotating antenna in a radome attached to the underside of the Avenger’s fuselage where it could look down on the low flying Kamikazes. The radome was so large that it destabilized the aircraft, necessitating two compensating tail finlets mounted on the horizontal stabilizer. It was not practical to carry the number of radar operators needed to detect and broadcast target data by voice radio to the ships below, so a means of broadcasting the entire PPI radar picture to shipboard operators was needed. This was solved by equipping the Avengers, designated TBM-3W, with a television-based transmitter and the ships with receivers and displays to show the airplanes radar picture. A radar beacon on the airplane allowed the shipboard operators to offset the center of the aircraft’s radar display to the location of the airplane so that the aircraft’s targets were displayed in the correct locations relative to each receiving ship. In addition to the pilot, the TBM-3W carried two operators who monitored the radar.
The TBM-3W system was still under evaluation at war’s end, so none of the aircraft saw combat, but the capability was felt important enough to continue the project. In 1948 a new Airborne Early Warning Squadron, designated VC-2, was equipped with the modified Avengers. [Gebhart, Louis A., Evolution of Naval Radio-Electronics and contributions of the Naval Research laboratory, NRL Report 7600, Naval Research Laboratory, Washington, D.C., Jan. 1976, pp. 207-208] [ Guarino, Thomas A. and Muller, Charles F., Jr., “The Eyes of the Fleet,” U. S. Naval Institute Proceedings, Vol. 102/10/884. Oct. 1976, p. 117]
Also in 1945 the Navy wanted a land based AEW airplane having longer range and longer staying time than the TBM-3W, and their solution was conversion of 48 Boeing B-17G Flying Fortresses to AEW use by installing an AN/APS-20E radar in a dome below the fuselage. These aircraft were also intended to provide early warning of Japanese air attack on fleet units, and were intended to go in harms way. They retained their guns for self defense, which was the main reason for choosing the heavily armed B-17. Again, the war was over before the PB-1W was ready for Pacific service, but the planes were used for many years to patrol the far North Atlantic on the lookout for Soviet air attack; and in fact remained at this duty after most other U.S. B-17s had been retired.
The Douglas AD Skyraider, a low wing craft powered by a large radial piston engine, was another airplane designed during World War II, but finished testing too late to see WW II combat. It was intended as a combination dive/torpedo bomber replacement for Grumman Avengers and Curtiss SB-2 Helldivers, and was first test flown in March 1945. In addition to bomber versions, 418 Skyraiders were fitted with the venerable AN/APS-20 search radar, with additional seats for two radar operators in addition to the pilot, and intended as a replacement for the aging TBM-3W carrier based AEW airplanes. As with the TBM-3W, additional tail finlets were needed to compensate for the destabilizing effect of the large radome slung under the fuselage. The AEW version served in three designations: AD-3W, 4W, and 5W during both the Korean and Vietnam wars.
Although not designated as an AEW aircraft the Grumman AF-2W ‘’Guardian’ was fitted with an under-fuselage AN/APS-20 search radar for the purpose of hunting submarines. It first flew in November 1948 and began fleet service in September 1950. It was the largest single engined, piston powered, aircraft ever flown from U.S. aircraft carriers. [Grumman AF Guardian, From Wikipedia, the free encyclopedia]
As a replacement for the aging B-17-based PB-1Ws the Navy in 1949 bought two four engined Lockheed Constellation transport airplanes with the intent to equip them with powerful search radars and evaluate them for AEW use. Designated PO-1W, the radar equipped Constellations were first test flown in June 1949, and demonstrated that they could be operationally useful in fleet support. In production, the airplanes were redesignated PO-2W, and later EC-121. [Armistead, Edwin L., AWACS and Hawkeyes - The Complete History of Airborne Early Warning Aircraft, MBI Publishing Company, St. Paul. MN, 2002, ISBN 0-7603-1140-4, pp. 20-25]
By mid 1950 the ’Cold War’ with the Soviet Union was well under way and in November of that year the United States and Canada began planning three lines of radar stations across the northern U.S. and Canada to provide warning of nuclear armed bombers winging their way from the USSR. The lowest of these lines ran roughly across the northern U. S. border, and the the furthest north, called the Distant Early Warning or DEW’ Line, ran across the far north of Canada above the Arctic Circle. In the beginning the maximum range of Soviet bombers required that they fly to the U.S. along a direct polar route, but there was concern that as the range of newer aircraft increased and as aerial refueling capabilities improved, the U.S. and Canada had to face the prospect of bombers circling by sea around the ends of the warning lines at low altitude. Thus in the early 1950s the Navy made the dual commitment to provide 22 destroyer escorts converted to radar picket ships and 142 radar equipped long range land based PO-2W airborne airborne early warning airplanes to extend the DEW line seaward.
Engineering physicist Leo M. Puckett had just joined the Radar and Control Systems Branch of the Bureau of Aeronautics Avionics Division in 1948, and because he had experience developing shipboard radars he was assigned to the group responsible for outfitting the two PO-1W experimantal Constellations each with two large radar sets. The planes were to be equipped with an AN/APS-45 height finding radar fitted in a large projection above the fuselage, and an AN/APS-20 long range search radar in a dome below the fuselage. Puckett and his group had to work out how to fit six tons of electronic equipment into the Constellation, and their work was rewarded by success. By mid 1956 forty five of an eventual 142 EC-121s, by then called by the popular name ‘Warning Star’ were flying barrier patrols in the North Atlantic and Pacific on the extended DEW Line. [Sinfas, Intelligence Specialist Second Class William J., USNR, “Flying the Barrier,” Naval History magazine, U.S. Naval Institute, Mar./Apr. 1994, Vol. 8 No. 2 pp. 15-16] [Puckett, Leo M., Interview with D. L. Boslaugh, 26 Sept. 1994]
Leo Puckett related to this writer that detecting low flying airplanes over the ocean was always a challenge for the Warning Star radar operators, and finding low flyers over land was impossible for them. The ability to lift a radar antenna to high altitude had its advantages, but also disadvantages. The radar was not only looking down on low fliers, abut also on sea or land surface. When the sea was calm the radar operators could easily see the aircraft below them, but as the sea surface roughened the waves also caused radar reflections that masked the airplanes they were trying to detect. This ‘sea clutter’ could get so bad that the airborne radar was useless. When the radar looked down on land it was totally blanked out. Low fliers could travel over land without fear of detection by airborne radars. Finding targets in sea clutter or land masking has always been a problem that somewhat vexes land based radars, is worse for shipboard radars, and extremely difficult for airborne radars. [Puckett interview] [Inman, Capt. Bryce D., USN, Letter to D. L. Boslaugh, 15 Aug. 1995]
There is one main difference between the radar return from an airplane and a return from sea or land clutter, caused by the airplane’s relative motion with respect to the earth’s surface. Since the invention of radar, radar engineers have tried to take advantage of the fact that airplanes are moving targets - to enhance their detection capability. Much research effort has been put into trying to develop a ‘perfect’ moving target indicator MTI). One of the earliest attempts at developing a moving target indicator used the slight change in frequency of a radar pulse reflected from a moving target called the Doppler shift. Doppler shift can be detected in a radar receiver as a slight change in amplitude of successive pulses in a train of pulses reflected by a moving target, because the strength of the return varies as the rate of a ‘beat frequency’ which is equal to the difference between transmitted pulse frequency and return pulse frequency. [Inman letter]
It is not possible to see the slight change in return pulse amplitudes on a conventional plan position indicator (PPI) radar scope, but there are ways of electronically enhancing the pulse differences. One of the earliest techniques used a mercury delay line, much like early computer delay line memories, to store a string of returned pulses, and then to save only the differences in strength of successive pulses. When these differences are summed up in another circuit, called an integrator, the summation can be large enough to create a blip on a PPI scope. Not many years after the invention of radar these moving target indicator circuits were incorporated into shipboard search radars with a useful increase in detection of moving targets masked by sea clutter. [Inman letter]
Devising a moving target indicator for an airborne radar has been a much more difficult challenge because the radar platform is also moving over the earth at fairly high speed. The Navy’s Bureau of Aeronautics as well as the USAF’s Lincoln Laboratory at the Massachusetts Institute of Technology worked on the problem for years producing new circuits and devices that increment-by-increment improved airborne radar’s ability to find targets in sea and land clutter. Because of his work in the EC-121 ‘Warning Star’ airborne radar system, Leo Puckett was one of the key persons in the Bureau of Aeronautics working on moving target indicator improvements.
By 1955 the Navy needed to think about a replacement for its AD-5W carrier based airborne early warning airplanes, but this time the operational requirement called for the aircraft to not only send its radar picture down to ships, but also to be able to control interceptors on its own. The need to carry a new, much larger, AN/APS-82 search radar as well as two air intercept controllers in addition to a pilot and copilot called for a twin engined aircraft. The plane would patrol at the relatively low altitude of 5,000 to 7,000 feet in order to minimize sea and land clutter returns. Also the craft was to have an automatic radio data link to receiving ships so that voice radio target data transmission would not be needed.
There was considerable urgency to get the new AEW airplane, so the Bureau of Aeronautics elected to base the craft on the existing Grumman S-2F ‘Tracker’ anti submarine aircraft instead of the longer process of a design competition. The AEW configuration was designated WF-2. The AN/APS-82 radar antenna envisioned for the WF-2 was far too big to sling under the fuselage as had been the APS-20 antenna. The new antenna had to be mounted atop the fuselage, and it was big, having about the same surface area than the airplane’s wings. [Armistead, p 44-45] [Guarino & Muller, p 117] Leo Puckett and his radar engineers in BUAER Code 5338 got the job of fitting the avionics into, and onto, the WF-2 airframe. Puckett remembers that the Bureau’s aerodynamicists at first couldn’t believe it when he showed them drawings of the huge radome he wanted to mount atop their aerodynamically clean aircraft. It took a lot of calculations and wind tunnel testing to work out how to keep the airplane in the air, and controllable, but they succeeded. Among other things they had to place large vertical stabilizers at the tips of the horizontal stabilizer to overcome the destabilizing effect of the huge radome.
In production the WF-2 was redesignated E-1B, and entered service in 1958 - with the popular name ‘Tracer.’ The Tracer’s two radar operators were equipped with PPI display scopes on which they did World War II style manual plotting with grease pencils. They estimated target speed and course from the series of grease pencil dots, and calculated speed and heading orders for their interceptors with the manual vector algebra of a maneuvering board. The operators had an analog data link over which they could send their radar picture to surface ships, or they could resort to voice radio target telling. Ships could also send their radar picture to the Tracer over the same data link, but Puckett notes the arrangement left much to be desired. The radar set was equipped with the latest in airborne moving target indicator technology, but the operators still had detection problems when the sea surface showed a lot of sea clutter, and the AMTI still could not find air targets flying over land. [Guarino & Muller, p 117] [Puckett interview] [De La Matter, Capt. Stephen T., USN, “Naval Aircraft of the Next Decade,” U. S. Naval Institute Proceedings, Vol. 100, No. 855, May 1974, p. 84]
The E-2A ‘Hawkeye’
The Office of the Chief of Naval Operations sent the McNally/Svendsen NTDS Technical and Operational Requirements paper to the Bureau of Aeronautics in late 1955, with instructions to start working on it as a tentative Navy operational requirement. The paper called for an airborne tactical data system with the same capabilities as NTDS and the Marine Tactical Data System - with one exception. It would not have to do the tactical data link net control function. As in the WF-2 system, it would be called an airborne early warning and control (AEW/C) system. OPNAV did not specify a particular airframe, or any new aircraft to carry the system, the concept was to be able to fit it into a variety of aircraft. [Guarino & Muller, p 117] [Applied Physics Laboratory, The Johns Hopkins University, Survey of Digital Weapons Systems, estimated publication date 1975, p. 2-4] [Puckett interview]
Leo Puckett was issued the requirements paper and designated Airborne Tactical Data System systems engineer. Puckett examined the document in detail, developed a list of all the required capabilities, and concluded that it was calling for things that no other airborne system had ever done. The needed technologies and components just did not exist, and he was going to have to launch research and development projects in a number of areas; in particular greatly improved airborne moving target indication. The project was going to be very high risk.
The McNally/Svendsen paper did not say that ATDS had to have a digital computer, it only listed functions and capabilities, among which was the requirement that it be able to exchange tactical data in digital format on the tactical data link. This meant that the airborne data link terminal had to be digital at least on its interface with the outside world. Puckett realized, however, that an analog computer capable of performing all the required functions would probably weigh more than most airplanes, not to mention the reliability problems of large analog computers. He felt that a small, light, but powerful, digital computer would be the only solution.
As had McNally and Svendsen when they were conceptualizing NTDS, Puckett and three of his engineers embarked on a nationwide tour of contractors who might be capable of, and interested in, developing the airborne system. When visiting each contractor they described the system requirements and showed their concept drawings. Then they asked each contractor how they would approach system development. They found that East Coast contractors usually advocated analog approaches, however some on the West Coast proposed digital technology, and seemed to know what they were talking about. One West Coast contractor, Litton Systems, Inc., gave the most convincing description of how they would build the system, and they were interested in trying.
Back at the Bureau of Aeronautics, Puckett’s office announced in the Government Commerce Bulletin Daily an invitation to bid on a Naval Airborne Tactical Data System. They did not, however, specify any particular airframe, and left airframe proposal up to the bidding contractors. Litton Industries responded with a proposal in early 1956 in which they proposed a flying combat information center to be carried aboard a Lockheed Constellation fitted with four turboprop engines. Puckett’s team liked the Litton proposal and were about to issue Litton a study contract, when the Office of the Chief of Naval Operations made a radical change in the ATDS operational requirement.
The new operational requirement called for a carrier-based aircraft to carry ATDS. Furthermore, the craft had to be able to remain on station at 30,000 feet for at least four hours, and it had to have an effective airborne moving target indicator that would work at the airplane’s loitering speed, and the AMTI had to be able to pick out low flying targets in the worst sea clutter. The new requirement also specified that the airplane was to carry only one radar that could measure target range, bearing, and height in a full 360 degree circle around the aircraft. Furthermore, the radar must a range of at least 250 miles and must be able to detect a medium sized air target at that range at any altitude from 50,000 feet to sea level. What had already been a challenging, high risk operational requirement was now incredibly challenging. [Puckett interview] In a design competition, Grumman Aircraft Corporation proposed a high-wing aircraft powered by two turboprop engines for maximum fuel economy and on-station loiter time. BUAER selected Grumman in March 1957 to design and build the new aircraft, designated W2F-1. It would be the first carrier-based plane to be designed from the start as an airborne early warning and control craft. [Northrop Grumman E-2 Hawkeye, From Wikipedia, the free encyclopedia]
The avionics system was clearly going to be the critical controlling factor in the new aircraft development, and because it needed an unusually large rotating radar antenna, the avionics and airframe would have to be developed as an integrated system. In the past BUAER had developed airplanes relatively independently from the equipment with which they would be fitted, and the airframe development was managed by a ‘class desk’ in the Aircraft Division. The class desk was the Bureau representative to the plane’s builder, and coordinated other Bureau divisions who supplied standard Government equipment such as guns, radar, and radio equipment to the builder. But it was clear in the case of the new AEW airplane, that airframe and avionics should be developed simultaneously by one manager having technical and funding control; in other words, a designated project manager.
In the fall of 1956, the Bureau established the W2F-1 project office with Captain Clyde J. Lee in charge. Leo Puckett reported to Capt. Lee as avionics system engineer with responsibility to oversee the development and integration of all ATDS subsystems, and to ensure they fit into and were integrated with the airframe. In addition to other project office personnel, various Bureau divisions and branches assigned engineers who would work only on the W2F-1 project. As with NTDS ships, in order to participate on the tactical data link, the airborne system had to know precisely where the airplane was, and in W2F-1 this would be done by an airborne inertial navigation system interfacing directly with the AEW/C computer. Two engineers of the Navigation Systems Branch, Ellis Hall and Paul Schrock were detailed to develop a new airborne terminal that would interface the plane’s Carrier Airborne Inertial Navigation System with the AEW/C system. Their CAINS terminal had to be capable of taking an umbilical cord input from the inertial navigation system of the aircraft carrier and aligning the accelerometers and gyros of the plane’s system within five minutes while the aircraft sat on the carrier deck prior to launch.
In the Communications Branch, Raymond Wolforth was assigned to develop the interceptor control data link interface with the W2F-1 computer and engineers Herbert Silverman and Mark Spies were to develop the aircraft’s tactical data link terminal and radio to enable interface with NTDS and MTDS. The Radar and Control Systems Branch made available Commander Frank Ewald and and engineer Kenneth G. Ormcur to be in charge of the new airborne radar, and assigned W. E. Wright, a data processing engineer, to be in charge of developing the airborne computer. A new IFF system had to be developed for the new radar, which task was assigned to IFF engineers Leroy Arrons and Herbert Carlson. [Puckett interview]
General Electric won the contract to develop the new AN/APS-96 airborne search radar.
It was required to have two dimensional search, height finding on all targets, and IFF built into one radar. The antenna would be housed in a 24-foot saucer shaped radome, and the antenna would be fixed in the radome so that the whole assembly rotated as one unit. The Mark 12 IFF antenna would be attached to the rear of the radar antenna array. The radar antenna would have three horizontal rows of elements to provide the height finding capability by measuring the time difference of arrival of a direct target echo and the echo of the same target reflected from the surface. Target height would be automatically computed for each target from these measurements, and having three rows of elements would prevent computational ambiguities. [Guarino and Muller, p. 117]
The height of aircraft carrier hangar decks impose a limitation the maximum height of carrier airplanes. In the case of the W2F-1 with its large destabilizing radar antenna, the airplane was going to need four vertical stabilizers to allow it to fit into the hangar decks of the older Essex Class aircraft carriers. Furthermore the radome needed to be separated from the fuselage to minimize radiation interference, and the operating height of the dome would not allow the craft to fit into Essex Class hangar decks. The solution was a jacking arrangement in the dome mount that allowed lowering it for stowage. This caused a need for the rotating triaxial wave guide joint, that fed the three rows of antenna elements, to have a telescoping arrangement. This would be one of the most severe engineering challenges of the project. Examples of the complex interaction between the airframe and the avionics are the tips of the four vertical stabilizers and the propellers that had to be made of fiberglass to prevent radar beam interference. [Puckett interview] [Guarino and Muller, p. 117] [Gunston, Bill, Grumman, Sixty Years of Excellence, Orion Books Division of Crown Publishing, New York, 1988, ISBN 0-517-56796-2, pp. 90, 92]
Another extremely difficult engineering challenge lay embedded in the new operational requirement; the need to pick low flying targets out of heavy sea clutter. Puckett sought expert technical advice in the person of Dr. Irving Reed who had worked at MIT’s Lincoln Laboratories developing USAF airborne radars. Reed consulted with a number of other experts, and they recommended a combination of pulse compression technology and the use of a quartz crystal surface acoustic wave detector. The device would eventually have the capability of integrating target echoes out of severe sea clutter. [Puckett interview]
In addition to the pilot and copilot the W2F-1 would have room for only three operators: a combat information center officer, an air control officer, and a radar operator. With only one radar operator, it was clear to Puckett that target detection and tracking would have to be fully automatic, with a limited manual backup mode in case of equipment failure. Tracking would be either fully automatic or manual. The Bureau of Aeronautics issued a contract to Litton Systems, Inc. to devise a signal processor that could do auto detection and automatic tracking of both raw video and IFF beacon returns, the latter being somewhat similar to the shipboard beacon video processor. [Puckett interview] [Northrop Grumman E-2 Hawkeye, From Wikipedia, the free encyclopedia]
Donald L. Ream of the Bureau of Ships Special Applications Branch was generally considered as the Navy’s computer expert, and Leo Puckett felt Ream was invaluable in helping them develop their new CP-588 airborne computer. Ream recommended ATDS use a magnetic core memory computer, but when Puckett made a review of the state of the art of magnetic core technology, he found core memories not only too heavy for airborne use but also very expensive. He had too many other unknowns with which to grapple, and could not afford to gamble on the weight, volume, and cost of core memories coming down as predicted by Ream. Puckett opted instead to use a rotating magnetic drum memory in the CP-588, and decided to load it with a fixed program in which instructions were executed in the order they were written on the drum - so that they could get the highest possible execution speed. [Puckett interview] [Gunston, p. 92] [De La Matter, p 84]
Puckett credits Lieutenant Commander Edmund Mahinske of the NTDS project office as another great source of help to ATDS in developing the airborne tactical data link equipment. He recalled that even though Mahinske, Major Sudhoff of the Marine Tactical Data System project, and Puckett sometimes had violent disagreements about data link standards and formats, they always showed a unified U.S. Navy position when meeting with international representatives at NATO data link standards meetings. In early 1961 the Bureau of Naval Weapons, the successor to the Bureau of Aeronautics, contracted with Collins Radio Company to develop the ATDS tactical data link equipment. This consisted of an HF data radio and a data terminal set, the assemblage of which was designated AN/USQ-52 A-Link Set. BUWEPS issued a separate contract for the ATDS interceptor control data link equipment, made up of a data terminal set and UHF radio, to Bell Laboratories [Puckett interview] [Naval Electronics Laboratory Center, San Diego, CA, Command and Staff Manual - Link 11 Programmable Data Terminal Set (PDTS), NELC TM-116, 1 Feb. 1977, pp 1-6] [Rockwell International Corporation, Commerce Bulletin Daily Synopsis No. 310]
As with the Marine Tactical Data System, the radar displays developed by General Electric were identical regardless of the function of the three operators using them. Each of the user consoles had two cathode ray tubes. One was a PPI radar scope able to show both raw video and artificial symbols from the computer, and the other was a readout unit on which an operator could call for amplifying information about a selected target.
Operators used a light pen to select a specific target for computer attention and to make entries to the computer. [Applied Physics Laboratory, Survey of Digital Weapon Systems]
General Electric did the first system integration and test of the major ATDS components at their plant in Utica, New York. To illustrate the importance placed on airframe and avionics integration, instead of lab benches GE installed the equipment in a replica of the W2F-1 fuselage covered with a copper skin; and dubbed the ‘copper queen.’ Following system testing at GE, Grumman built a more complete system assemblage that included all ATDS equipment including computer, displays, radar, IFF, inertial navigation system, data links and the complete rotodome assembly - down to the telescoping triaxial wave guide joint. The prototype W2F-1 made its maiden flight, without the system aboard, in October 1960. Following that, Grumman disassembled the lab test system and installed it in the prototype aircraft. [Puckett interview] [Guarino and Muller, p. 117] [Gunston, p. 90, 92]
In the mean time, the ATDS project office had installed a land based ATDS system at the Naval Missile Center at Point Mugu, CA, and in October and November 1962 ran ATDS/NTDS compatibility tests with the land based NTDS system at the Fleet Computer programming Center, San Diego. Also in 1962, the designation of the prototype W2F-1 was changed to E-2A, and in mid 1963 the prototype was flown to the West Coast where it went aboard the attack carrier Oriskany for flight testing with the carrier’s service test Naval Tactical Data System. The Bureau of Naval Weapons authorized production of 62 E-2As, and Grumman started deliveries to Navy squadrons in January 1964. [Bureau of Ships,Technical Development plan for the Naval Tactical Data System (NTDS) - SS 191, 1 Apr. 1964, pp 4-7] [Dictionary of American Naval Fighting Ships-Volumes I-IIIV, United States Government Printing Office, Washington, D.C. 1964-1981, Vol V, p 174]
The E-2B Hawkeye
Two more attack carriers USS Kitty Hawk and Ranger arrived in the Gulf of Tonkin in November 1965. Both were carrying a complement of new E-2A airborne early warning and control aircraft on their first combat deployment. They were put into service immediately and showed they could digitally link their radar picture down to NTDS equipped ships, greatly extending their radar horizon. They showed they could automatically direct F-4 Phantom fighters to accurate intercepts, and they showed their adeptness at directing search and rescue missions from their airborne perch. They could also warn friendly aircraft away from enemy missile sites and from the Red Chinese border. When ATDS worked, the fleet was very pleased with it. [Cagle, Vadm. Malcolm W., USN, “Task Force 77 in Action off Vietnam,” U.S. Naval Institute Proceedings, Vol. 98, No. 831, May 1972, pp. 75-83]
When the squadrons of Hawkeyes started operating from carriers, things started to go wrong. Failures throughout the avionics system were much more frequent than predicted. This was found to be caused mainly by inadequate cooling of the electronics. Furthermore, even though Grumman was a leader in building seagoing aircraft, the E-2A was found unacceptably subject to airframe corrosion. Things got so bad that BUWEPS cancelled Grumman’s contract in January 1965 after 59 out of the 62 ordered aircraft had been delivered. [Armistead, pp. 48-49] [Northrop Grumman E-2 Hawkeye, From Wikipedia, the free encyclopedia]
In mid 1966 an Armed Forces Management Magazine reporter visited ships in the Gulf of Tonkin and noted in his article that E-2A Hawkeyes were operating from carriers in the Gulf. He stated that just one of the airplanes could process the same air target detection and tracking volume as one guided missile frigate equipped with NTDS. He also observed that although the Hawkeye’s radar could not pick up air targets over land, its automatic IFF beacon tracker could find all friendly targets, and the system depended heavily on the IFF tracker. When ATDS worked, it worked well and was highly appreciated. The problem was, ATDS was still not working all the time. It was found that its drum-based computer, in particular had two major problems. It was experiencing too many failutes, and furthermore, as operating experience was gained the new users constantly asked for changes in its computer program. Even though the program changes themselves were not particularly complex, the process of making changes to the fixed program on the memory drum was complex and unwieldy. Not long after initial deployment, the ATDS project office realized the drum-based CP-588 must be replaced by a general purpose, stored program machine with magnetic core memory. [Armed Forces Management Magazine, ‘For the Sea Going Services, The Naval and Marine Tactical Data Systems are the Best Since Radar,” Armed Forces Management, July 1966, p. 81] [Puckett interview]
The ATDS project office picked a Litton Systems dual processor L-304F avionics computer as replacement for the CP-588. Its 32-bit magnetic core memory could contain 80,000 random access words, with a cycle time of 2.2 microseconds. This was a fast computer. The Bureau tested the machine aboard a fleet E-2A in 1967, and found the change successful. The project had also worked out a number of other improvements to the avionics, including improved cooling, and better corrosion protection for the airframe. Forty nine of the E-2As were upgraded with the improvements, and redesignated as E-2Bs [Puckett interview] [Northrop Grumman E-2 Hawkeye, From Wikipedia, the free encyclopedia]
The E-2C Hawkeye
The airborne early warning capability provided by the Hawkeyes in the Gulf of Tonkin was much appreciated by the Task Force 77 commander, and normal operations in the Gulf called for at least one Hawkeye in the air at all times. Even with the reliability improvements of the E-2B, there were still times when the task force couldn’t get enough of the planes in the air. In addition to still remaining avionics reliability problems, the airplanes needed a lot of hangar time just to perform required preventive maintenance on their electronics. The squadrons wanted at least a tripling of E-2B availability through more reliable equipment and less maintenance down time.
The Bureau of Naval Weapons that had been formed by merger of BUORD and BUAER in 1959, lasted only until 1966 when it was split apart again; the components that came from the old Bureau of Aeronautics being formed in to a new Naval Air Systems Command (NAVAIR). NAVAIR was well aware of the fleet feeling about the Hawkeyes’ performance. In 1968 NAVAIR prepared specifications for a new production run of Hawkeyes, to be designated E-2C. The specification called for a fourfold increase in avionics reliability in company with greatly reduced preventive maintenance requirements. They also called for increased altitude and loiter time on station. The new craft was to be fitted with an improved AN/APS-120 radar with improved display system, and the addition of a passive detection system designated ALR-59. NAVAIR issued the contract to Grumman in June 1968. [Guarino & Muller, p 118] [Applied Physics Laboratory, p. 2-1]
The Litton L-304 computer was one of the few items carried over from the E-2B to the C. The L-304 still had considerable reserve computing capacity, and the new specifications called for detecting and tracking 300 radar and IFF tracks and at the same time tracking 350 passive detection reports from the ALR-59. The system was also required to run 20 simultaneous automatic air intercepts. The prototype E-2C was first test flown in January 1971. NAVAIR authorized production of 55 of the new craft, and the first production E-2C was test flown in September 1972. By June 1973, C version airplanes were being delivered to squadrons. [Applied Physics Laboratory, p. 2-1] [Gunston, p. 94] [Northrop Grumman E-2 Hawkeye, From Wikipedia, the free encyclopedia]
Operational experience showed that the reliability improvement program was well worth the expense. Records kept from Oct. 1975 to Mar. 1976 showed that during the six-month period the average flying hours of the new craft were higher than any other carrier aircraft model in the Navy. Furthermore, the E-2C had one of the highest operational readiness figures, and one of the lowest ratios of maintenance time to flying time of any USN carrier aircraft type. [Guarino & Muller, p. 1119] Hawkeyes are still flying in the fleet in 2011 in E-2C and D versions, and their expected life span is many years into the future. In addition to the U.S. Coast Guard and U.S. Customs Service, Hawkeyes are used by the armed forces of Egypt, France, Israel, Japan, Singapore, and Taiwan. [Northrop Grumman E-2 Hawkeye, From Wikipedia, the free encyclopedia]
The Antisubmarine Airplanes Go Digital
The P-3 Orion Land Based Maritime Patrol Craft
In 1957 the U.S. Navy sought to replace its aging fleet of twin piston engined, land based Lockheed P-2V ‘Neptune’ maritime patrol airplanes who's primary mission was to detect and track Soviet fast attack and ballistic missile submarines, and in the event of hostilities to attack and destroy them. In response to a request for proposals, Lockheed Aircraft Co. proposed a militarized version of their four turboprop engined airliner then under development, and intended as a competitor to the Boeing 707. Lockheed was the competition winner, and in May 1958 the Bureau of Aeronautics awarded an R&D contract to start redesign of the airframe. Lockheed first flew the resultant YP-3A aerodynamic test bed in August 1958.
The P-3 was intended to be a fighting aircraft and was fitted with an internal bomb bay as well as wing hardpoints to carry depth charges, anti sub torpedoes, guided missiles and bombs. Avionics equipment included an airborne radar with antenna in the plane’s nose, a magnetic anomaly detector (MAD) mounted in a fiberglass housing projecting from the tail, air dropped acoustic sonobuoys and on-board receiver, infra red detectors and an inertial navigation system. The plane was crewed by three pilots, a tactical coordinator flight officer, a navigator/communicator flight officer, two enlisted flight engineers, three enlisted sensor operators, and an enlisted aviation ordnanceman. Target plotting was done by hand, and coordination with other ASW airplanes and ships was by voice radio. First deliveries to Navy squadrons was in August 1962. [Lockheed P-3 Orion, From Wikipedia, the free encyclopedia]
As early as 1960 the Navy’s airborne antisubmarine warfare community had been watching the progress of NTDS and ATDS with interest. They questioned, could not the technologies that the two programs were developing also be applied to the P-3 project? The office of the Chief of Naval Operations asked the Bureau of Naval Weapons to study the possibilities, and BUWEPS, in turn, tasked the Naval Air Development Center at Johnsville, PA, to undertake the project. In particular they wanted to know if the P-3s could be equipped to participate on the NTDS tactical data link. This would greatly improve coordination among surface and air ASW units, as compared to the present use of voice radio; and ASW had to be a highly coordinated game.
The Orion’s mission was wide ocean area surveillance, submarine detection, and submarine destruction. The primary functions of its operators and equipment were; accurate navigation over water, viewing and processing data from its sensor systems, determining submarine location as accurately as possible, and helping the pilot steer the airplane to submarine location. The envisioned automated system would normally use the NTDS A-Link only for exchanging sub location and track information with surface ASW ships and other ASW airplanes. [Applied Physics Laboratory, pp. 3-1 - 3-5]
OPNAV also wanted a way to digitize all submarine contact data from the P-3 sensor systems (MAD, acoustic, radar, infra red, ECM intercepts, and visual) and send it to a digital processor that would correlate all inputs. This would improve probability of submarine detection, and tracking accuracy. NADC began with a laboratory mockup of the P-3 systems and devised ways to manually enter readings from the sensor systems into a borrowed NTDS CP-642B unit computer. Once the data was in the unit computer, it would not be difficult to participate on the A-Link with a suitable modem and radio - and BUWEPS was already developing these for ATDS. They got encouraging results in the lab and in 1963 BUWEPS contracted with Univac to build an airborne version of the CP-642B computer.
The resultant CP-823U computer was condensed considerably in size from the unit computer dimensions through use of first generation microelectronics technology. Next NADC installed the prototype computer and input devices in a P-3 where flight testing also showed encouraging results. Next came another laboratory system using results from flight testing, and then another flying system, after which NADC was ready to write production specifications for the equipment. The production CP-901 avionics computer was given 131 thousand 30-bit words of magnetic core memory, had a volume of only 7.4 cubic feet and weighed 306 pounds. Production computer deliveries began in 1967, and the Naval Air Systems Command named the P-3 upgrade system A-NEW (standing for ASW-NEW) [Applied Physics Laboratory, p. 3-1 - 3-4] [Lockheed P-3 Orion, From Wikipedia, the free encyclopedia]
P-3 Orions are still flying in 2011, and have been through several upgrades, primarily to their avionics systems which are now fully automatic from sensor to computer with manual entries no longer required. The planes normally fly 12 hour missions at about 200 feet above the sea, and can stay up much longer if necessary by aerial refueling, the primary constraint on mission length being crew fatigue. The latest version is the P-3C that has gone through four upgrades. To date, 737 P-3s have been built, and serve in numerous navies in addition to the U.S. Navy. [Lockheed P-3 Orion, From Wikipedia, the free encyclopedia]
The S-3 Carrier Based ASW Airplane
By 1968 the Grumman ‘Tracker’ carrier based ASW airplane had been on active duty for more than 14 years, and technology had passed it by. It was in need of modern replacement, and what the Navy wanted was a carrier based ASW plane with digital capabilities similar to the P-3. The Naval Air Systems Command , in August 1969, signed a contract with Lockheed Aircraft to design and build eight prototype and engineering development aircraft for testing. If the airplane performed as hoped, there was the potential for buying 191 more. The contract called for a subcontract with Univac to provide a central airborne digital computer. [Lawson, Robert L., “The Viking at sea” U.S. Naval Institute Proceedings, Vol. 105/7/917, July 1979, p. 71]
Univac proposed an airborne version of the Navy standard AN/UYK-7 computer - that will be described in a following chapter. The resultant AN/AYK-10 avionics computer was actually two 32-bit UYK-7s installed in a common cabinet and which shared a common memory. The S-3 was given an improved acoustic system processing capability as compared to the P-3, and improved operator displays. The number of required operators was reduced to two primarily by providing digitized outputs from the sensor systems directly into the digital computer. As with the P-3, the S-3 was not a regular participant on the NTDS A-Link, but rather used it when necessary to trade submarine contact data with other ASW airplanes and ships. [Frost, Cecil R., “Military CPUs,” DATAMATION Magazine, 15b July 1970, pp. 87-90] [Applied Physics Laboratory, p. 4-1, p. 4-3] [Holmes, Tony and Montbazet, Jean-Pierre, Carriers - United States Naval Air Power in Action, Military Press, New York, 1990, ISBN 0-517-01219-7, p. 176]
Lockheed took the prototype S-3 ‘Viking’ up on its first test flight on 21 January 1972. System testing showed that with advanced automation, Lockheed had indeed been able to pack most of the P-3s capabilities into a much smaller airframe, crewed by only four persons and powered by two General Electric turbofan engines. Like the P-3 the Viking was equipped not only to find and track submarines, but to kill them if called for. To carry mines, depth charges, bombs, rockets and other weapons the S-3 was fitted with two internal weapons bays and two wing hard points. Testing showed that the new craft had a combat range of over 500 miles using internal fuel only, and that it could loiter on station for five hours. Aerial refueling capability allowed the plane to stay up indefinitely, so that, as in the case of the P-3, endurance was limited only by crew fatigue.
The engineering development S-3s began Navy acceptance testing at the Patuxent River Naval Air Test Center in October 1973, and first fleet deliveries were made in February 1974. As opposed to the P-3s wide area surveillance mission, the S-3s mission is primarily local area task force defense against submarines. [Lawson, pp. 72-73]