M-28 Davy Crockett

The M-28 Davy Crockett Weapon System was a tactical nuclear recoilless gun for firing the M388 nuclear projectile that was deployed by the United States during the Cold War. Named after American soldier, congressman, and folk hero Davy Crockett, it was one of the smallest nuclear weapon systems ever built.

The Davy Crockett was developed in the late 1950s for use against Soviet troops had war broken out in Europe. Small teams of the Atomic Battle Group (charged with operating the device) would be stationed every few kilometers to guard against Soviet attack, using the power of their nuclear artillery to kill or incapacitate advancing troop formations and irradiate the area so that it was uninhabitable for up to 48 hours, long enough to mobilize NATO forces.

The M-388 round used a version of the W54 warhead, a very small sub-kiloton fission device. The Mk-54 weighed about 51 lb (23 kg), with a selectable yield equivalent to 10 or 20 tons of TNT (very close to the minimum practical size and yield for a fission warhead).
The recoilless gun proved to have poor accuracy in testing, so the shell's greatest effect would have been its extreme radiation hazard. Even at a low yield setting, the M-388 would produce an almost instantly lethal radiation dosage (in excess of 10,000 rem) within 500 feet (150 m), and a probably fatal dose (around 600 rem) within a quarter mile (400 m).