The W31 was an American nuclear warhead used for two US missiles and as an atomic demolition munition. The W31 was produced from 1959, with the last versions phased out in 1989. All versions were roughly the same dimensions and weight: 28 to 30 inches in diameter, 39 to 39.5 inches long, and weighing 900 to 945 pounds. The W31 is a boosted fission nuclear bomb.