British radar developments in pulsed radar prior to 1938
All of the above is correct. As Guerlac and many others state, the original ionospheric experiments used pulsed signals. These experiments were known by all radio physicists worldwide. Hence, based on the results of these experiments, the possibility of the use of pulses for detecting the distance of targets was picked up by many countries, leading to the development of pulsed radars. (Note also that most countries, including the Soviet Union, developed cw (continues-wave) radars at the same time.) What makes the Zenit development unique, in my opinion, is the simultaneous use of three significant elements: pulses, microwave magnetron transmitters, and parabolic antennas.(Most of the earlier radars used tube transmitters rather than magnetrons, which were better suited to microwave frequencies.) The resulting system, although not without its flaws, was capable of measuring target range (distance),altitude, and azimuth.