... DoD illustration (Gordon Phillips) of 'Project Pluto' nuclear powered ramjet. This was an idea for an unmanned 'SLAM' ( Supersonic Low Altitude Missile). After disposable booster rockets got it aloft and up to supersonic speeds an unshielded light-weight atomic reactor became the heat source for the Mach 3 ramjet. No conventional fuel was needed. Range and time aloft was virtually unlimited.
The design called for a payload of multiple atomic weapons which could be ejected at given points on various targets along the flight plan. Just the shockwave of the vehicle passing over at tree-top level at Mach 3 could kill you. Then there was the matter of that unshielded reactor irradiating and poisoning large swaths of land as it criss-crossed across the USSR. Nicknamed 'the flying crowbar' a swarm of these death birds could continue operating weeks after anyone was left to kill or care. The Pentagon abandoned plans for the locomotive sized missile after analysis concluded it was just too ... crazy!
Recently Russia has been looking into cheap and scary new ways to intimidate US and Nato; their SSC-X-9 Skyfall is a rebirth of the basic concept. Dr. Strangelove would approve!
In 1958 a science-fiction movie was made with a suspiciously similar 'monster' LINK