As part of the Aircraft Nuclear Propulsion Program, the U.S. conducted extensive research showing that nuclear fission could power an aircraft. The research involved a series of Heat Transfer Reactor Experiments (HTREs), which tested if different types of jet engines could be run by nuclear power. In 1955, however, the project was cancelled, and a safe, operational prototype aircraft was never developed. In this 1988 photo, the two HTRE reactors are shown in transport to Idaho National Laboratory's EBR-1 visitor center, where they remain today. | Photo courtesy of Idaho National Laboratory.