A nuclear-powered aircraft is a concept for an aircraft intended to be powered by nuclear energy. During the Cold War, the United States and Soviet Union researched nuclear-powered bomber aircraft, the greater endurance of which could enhance nuclear deterrence, but neither country created any such operational aircraft. One inadequately solved design problem was the need for heavy shielding to protect the crew from acute radiation syndrome. The advent of ICBMs in the 1960s greatly diminished the tactical advantage of such aircraft, and respective projects were cancelled; the inherent danger of the technology has prevented its civilian use.