Project Pluto

In the 1950s, U.S. government was working on Project Pluto to develop cruise missiles that had a “nuclear ramjet,” which would use a nuclear reactor to heat incoming air and use that heated/expanded air for propulsion. The missiles could stay airborne for months, cruising in circles over the ocean until ordered onto a target. It would spew radioactive material over any area it was flying over. The project was abandoned when the ICBMs became more practical, fortunately.