The B28, originally Mark 28, was a thermonuclear bomb carried by U.S. tactical fighter bombers, attack aircraft 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. In addition, certain USN carrier based attack aircraft such as the A3D (later A-3B) Skywarrior, A4D (later A-4) Skyhawk, and A3J (later A-5A) Vigilante were equipped to carry the MK 28.