Forty-six years ago this month, the United States abandoned a 7-year effort to develop a nuclear-armed, supersonic cruise missile. The joint USAF-AEC program was known as Project Pluto. The centerpiece of this program was the nuclear-fueled, ramjet-powered Supersonic Low-Altitude Missile (SLAM).
The 1950′s saw the development of myriad aircraft, missile and submarine concepts designed for delivery of nuclear weaponry over strategic distances. This developmental activity was driven by the escalating Cold War between the United States and the Soviet Union. In addition to weapons, the power of the atom was also considered for propulsion applications during this era.
SLAM was perhaps the most fearsome weapon ever conceived. The missile was designed to deliver as many as 26 nuclear bombs over the Soviet Union in a single mission. It would do this while flying at Mach 3 and less than 1,000 feet above ground level. SLAM's shock wave overpressure alone (162 dB) would devastate structures and people along its flight path. And, as if that were not enough, the type's nuclear-fueled ramjet would continuously spew radiation-contaminated exhaust all over the countryside.
http://blog.seattlepi.com/americanaerospace/archives/214256.asp