The B28 (originally Mk 28) was a thermonuclear bomb carried by U.S. tactical fighter bombers and bomber aircraft. From 1962 to 1972 under the NATO nuclear weapons sharing program, American B28s also equipped six Europe-based Canadian CF-104 squadrons known as the RCAF Nuclear Strike Force. It was also supplied for delivery by UK-based Royal Air Force Valiant and Canberra aircraft assigned to NATO under the command of SACEUR.
20 different versions were offered, distinguished by their yield and safety features. The B28 used the ‘building block’ principle, allowing various combinations of components for different aircraft and roles. The principal configurations were:
The B28 had a diameter of about 22 in (58 cm), with a length varying between 96 in (2.44 m) and 170 in (4.32 m) and weight of 1,700 lb (771 kg) to 2,320 lb (1,053 kg), depending on version. Explosive yield was 1.1 megaton for Mod 1 warheads, 350 kiloton for Mod 2, 70 kiloton for Mod 3, and 1.45 megaton for Mod 5. It could be configured for air burst or groundburst detonation. 4,500 B28s were produced. The last examples were retired in 1991.