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I agree that this is not an invention but IEEE Milestones aren't retricted to inventions. The broadest definition says that the program recognized "technological achievements". A little more detail is provided in the statement "Milestones recognize the technological innovation and excellence for the benefit of humanity found in unique products, services, seminal papers and patents." The Rincon del Bonete project could be construed as a "product" (a big one)that provided a "service" (electrification of the country) and is probably unique in the way it was redesigned in the middle of a great war. Certainly it was an achievement.