[catalogia]

It's my understanding that if not for the development of ICBMs, the US might have created cruise missiles powered by unshielded nuclear reactors. They got as far as running a prototype engine for five minutes, but the whole project became pointless when it became clear ICBMs would work.

https://en.wikipedia.org/wiki/Project_Pluto

Russia has seemingly been developing this same sort of technology in recent years. Presumably this is in response to anti-ballistic missile technology calling into question the future effectiveness of ICBMs.

https://en.wikipedia.org/wiki/9M730_Burevestnik