The Davy Crockett
The Davy Crockett was a Recoilless rifle that fired a portable nuclear warhead, the M338, that detonated with force equal to around 10 and 20 tons of TNT, or 40–80 Gigajoules.
It’s users were advised to shoot it and get the hell out of there as fast as possible, as the warhead had an instant kill distance of 500 ft (150m) and a possible lethal dose of radiation at around a quarter mile (400m)
Unlike many experimental weapons, this one actually entered service, from 1961–1971.
That’s all folks!