The Convair NB-36H (bottom) was a converted B-36 Peacemaker bomber, used to test the concept of nuclear-powered aircraft. Built as part of the Aircraft Nuclear Propulsion (ANP) program, the plane carried an operational 1-megawatt nuclear reactor, although this did not power the plane. The NB-36H flew 47 flights between 1955 and 1957, but the ANP program was ultimately canceled. In this flight, the NB-36H is shown shadowed by a Boeing B-50 Superfortress (top).Photograph: United States Air Force