29 1962 Small Mobile Power Plant The U.S. Army experimented in Idaho and elsewhere in pursuit of small nuclear power plants. Its “mobile” prototype, ML-1, arrived in Idaho for field testing via an Army semitrailer from Aerojet-General in Downey, California.The reactor first went critical in 1961 and operated as a power plant for the first time on Sept. 21, 1962, making history as the smallest nuclear power plant on record to produce electricity. It reached full power operation on Feb. 28, 1963, and its first run continued until March 4, 1963. Riddled with leaks, failed welds and other problems due to operating temperatures that exceeded material thresholds, ML-1 shut down for good May 29, 1964. Yet a number of small portable reactors deployed to remote Army bases operated reliably for years.