The Convair X-6 was a proposed experimental aircraft project to develop and evaluate a nuclear-powered jet aircraft. The project was to use a Convair B-36 bomber as a testbed aircraft, and though one NB-36H was modified during the early stages of the project, the program was canceled before the actual X-6 and its nuclear reactor engines were completed. The X-6 was part of a larger series of programs, costing US$7 billion in all, that ran from 1946 through 1961. Because such an aircraft's range would not have been limited by liquid jet fuel, it was theorized that nuclear-powered strategic bombers would be able to stay airborne for weeks at a time.