During the Cold War research was conducted by both the USA and the Soviet Union into military aircraft that could stay aloft for months at a time, powered by a nuclear reactor. The USA used a converted B-36 bomber which flew 47 test flights between 1955 and 1957. An onboard nuclear reactor was operational during some of these tests but never powered the aircraft. The Soviets performed similar experiments from 1961 to 1965 using a Tupolev Tu-119. Both projects were ultimately cancelled.