During the Cold War the United States designed and ground-tested a nuclear-powered ramjet called Project Pluto. This system used no combustion - a nuclear reactor heated the air instead. The project was ultimately canceled because ICBMs seemed to serve the purpose better, and because a low-flying missile would have been highly radioactive.
Nuclear powered ramjets
During the Cold War the United States designed and ground-tested a nuclear-powered ramjet called Project Pluto. This system used no combustion - a nuclear reactor heated the air instead. The project was ultimately canceled because ICBMs seemed to serve the purpose better, and because a low-flying missile would have been highly radioactive.