Shot Socorro was the 22nd nuclear detonation of Operation Hardtack II, fired on 22 October 1958 from a balloon at 442 metres above Area 7b of the Nevada Test Site. It was the first successful full-yield test of the XW-54 primary, producing 6 kilotons against a predicted 5–9 kt — a milestone that had eluded the programme through a long series of fizzles. The device weighed just 26 kg. The W-54 became the smallest nuclear weapon in both weight and yield ever to enter US service, deployed in the M-388 Davy Crockett recoilless gun projectile — a man-portable battlefield nuclear system assigned to US Army units in West Germany for use against Soviet armoured forces. The Davy Crockett warhead was withdrawn from West Germany in August 1967. The B-54 Special Atomic Demolition Munition variant, a backpack-carried nuclear demolition charge, remained in service until 1989.