B28 nuclear bomb
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 U.S. Navy 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.
The Mk 28 was produced from 1958 through 1966. It used the W28 lightweight, Class D warhead (also shared with the TM-76 Mace surface-to-surface missile and the GAM-77 Hound Dog air-launched cruise missile). After 1968 it was redesignated B28.
Twenty different versions of the B28 were made, 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 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 the model type and whether a parachute retard pack was fitted. The principal configurations were:
- B28EX — (EXternal), streamlined external-carriage version for free-fall delivery (no parachute)
- B28RE — (Retarded External) streamlined external-carriage version with a parachute retarder (4 ft. pilot, 28 ft. ribbon chute)
- B28IN — (INternal) unstreamlined internal-carriage version for free-fall delivery, primarily for the Republic F-105 Thunderchief
- B28RI — (Retarded Internal) unstreamlined internal-carriage version with parachute retarder
- B28FI — (full Fuzing Internal) unstreamlined internal-carriage version with parachute for laydown delivery; used only by SAC B-47s and B-52s. The FI, for "Full Fuzing Internal" was developed to adapt to new low-level delivery techniques of the Air Force in the 1960s, and is the only model of this bomb equipped for air, ground, and delayed action burst.
The range of explosive yields was:
- Mod 1 — 1.1 megaton TNT equivalent
- Mod 2 — 350 kiloton TNT equivalent
- Mod 3 — 70 kiloton
- Mod 5 — 1.45 megaton
The B28 bomb design has been described as the origin of a series of related nuclear warheads designated W28 or Mk28. The W28 designation was used for two USAF missiles the MGM-13MACE surface to surface and the AGM-28 Hound Dog air to surface systems. Each had a variable yield set by the Mod number at time of manufacturing ranging from a low 70 kt yield to a high 1,450 kt yield. This same 'physics package' was used for all five aircraft dropped bombs as well as the missiles.
The nuclear fission first stage or primary, code-named the Python primary, was reused in several subsequent weapons. The B28 was the mainstay of SAC during the Cold War and have yet to be completely dismantled by the Defense Department (as of 2012).
Accidents and incidents
The Canadian War Museum, in Ottawa, holds a Mark 28RE training variant in its Cold War gallery. The Mark 28 armed CF-104 Starfighters in Germany, 1963–72, under the "Dual Key" protocol (both the US and Canada had to agree to use, with the weapons in US custody on Canadian bases).
- B28 Nuclear bomb (United States), Jane's Information Group, retrieved 2008-11-10
- MARK 28 THERMONUCLEAR BOMB Archived 2013-04-04 at the Wayback Machine // National Museum of the USAF, 8/16/2012: "The artifacts on exhibit are BDU-16/E training variants of the Mk-28 and are displayed on an MHU-7/M Bomb Lift Trailer... return to the Cold War Gallery."
- John Clearwater (1998). Canadian Nuclear Weapons: The Untold Story of Canada's Cold War Arsenal. Dundurn Press. pp. 91–116. ISBN 1-55002-299-7. Retrieved 19 December 2016.
- Complete List of All U.S. Nuclear Weapons, The Nuclear Weapon Archive