Mark 7

The Mark 7 (also designated Mk-7 or "Thor") was the first tactical fission bomb adopted by the United States armed forces. Developed for carriage by smaller aircraft, it was the first nuclear weapon delivered via toss bombing using the low-altitude bombing system (LABS). Initial testing occurred during Operation Buster-Jangle. The weapon entered service in 1952 and remained operational until the late 1960s. A development program initiated in February 1953 for an atomic demolition munition variant designated T2 was canceled prior to production.

The Mark 7 was an implosion-type nuclear weapon utilizing a levitated pit and 92 high-explosive lenses. It featured a variable-yield design, offering selectable yields of 8, 19, 22, 30, 31, and 61 kilotons depending on the specific weapon pit installed. Fuzing options included both airburst and contact modes. For safety, early variants utilized an automatic in-flight insertion system, while later models transitioned to a PAL A arming and safing system. The bomb was configured with a single vertical retractable stabilizer fin to facilitate carriage within internal bomb bays or on external underwing pylons.

The weapon's warhead, designated W7, was adapted for several other delivery systems. These included the BOAR air-to-surface rocket, the MGR-1 Honest John tactical surface-to-surface missile, the MGM-5 Corporal ballistic missile, the MIM-14 Nike Hercules surface-to-air missile, and the Mark 90 Betty nuclear depth charge.

The Mark 7 was widely deployed by United States forces and supplied to the Royal Air Force (RAF) of the United Kingdom for use on Canberra aircraft assigned to NATO forces in Germany. This transfer occurred under Project E, a bilateral agreement governing the carriage of US nuclear weapons by British aircraft. In RAF service, the weapon received the designation H.E. M.C. Delivery platforms for the gravity bomb and BOAR configurations included the F-84 Thunderjet, F-100 Super Sabre, F-101 Voodoo, B-57 Canberra, F3D-2B Skyknight, A-1 Skyraider, A-3 Skywarrior, A-4 Skyhawk, F2H Banshee, F3H Demon, FJ Fury, and B-45 Tornado.

During Operation Teapot MET on April 15, 1955, a test was conducted using a Mark 7 warhead configured with an experimental composite plutonium/uranium-233 pit. The test produced a 22-kiloton yield, which was lower than projected and affected several military effects experiments scheduled for the event.