Design and development
The Aircraft Nuclear Propulsion (ANP) program, and the preceding Nuclear Energy for the Propulsion of Aircraft (NEPA) project, worked to develop a nuclear propulsion system for aircraft. The United States Army Air Forces initiated Project NEPA on May 28, 1946. After funding of $10 million in 1947, NEPA operated until May 1951, when the project was transferred to the joint Atomic Energy Commission (AEC)/USAF ANP. The USAF pursued two different systems for nuclear-powered jet engines, the Direct Air Cycle concept, which was developed by General Electric, and Indirect Air Cycle, which was assigned to Pratt & Whitney. The program was intended to develop and test the Convair X-6, a planned prototype for a fully functional nuclear-powered plane.
In 1952, the Carswell Air Force Base in Texas was hit by a tornado, severely damaging a number of aircraft. One of the damaged planes was a B-36 bomber, and Convair suggested to the Air Force that it should be converted into an early prototype for the X-6, instead of being repaired. The Air Force agreed to this plan, and provided funding for an overhaul of the plane. The intention was to test flying a plane with a functioning nuclear engine on board, but with it not yet powering the plane at this stage.
The original crew and avionics cabin was replaced by a massive lead- and rubber-lined 11 ton crew section for a pilot, copilot, flight engineer and two nuclear engineers. Even the small windows had 25–30 centimetres (10–12 in) thick lead glass. The aircraft was fitted with a 1-megawatt air-cooled reactor, with a weight of 35,000 pounds (16,000 kg). This was hung on a hook in the middle bomb bay to allow for easy loading and unloading, so that the radioactive source could be kept safely underground between the test flights. A monitoring system dubbed "Project Halitosis" measured radioactive gases from the reactor.