The B61 nuclear bomb is the primary thermonuclear weapon in the U.S. Enduring Stockpile following the end of the Cold War.
Development
The B61, originally known (prior to 1968) as the Mk 61, was designed in 1963. Testing began in 1966, with full production beginning in 1968. Total production of all versions was approximately 3,155, of which approximately 1,925 remain in service as of 2002. The warhead has changed little over the years, although early versions have been upgraded to improve their safety features.
The basic physics package of the B61 is shared with the W80 warhead used by several U.S. cruise missiles.
The B61 has been deployed by a very wide variety of U.S. military aircraft. Aircraft cleared for its use have included the B-1, B-2, B-52, and FB-111 strategic bomber aircraft; the F-100 Super Sabre, F-104 Starfighter, F-105 Thunderchief, F-111 and F-4 Phantom II fighter bombers; the A-4 Skyhawk, A-6 Intruder, and A-7 Corsair II attack aircraft; the F-15 Eagle and F-15E Strike Eagle, F-16, F/A-18 Hornet and Super Hornet; and the F-117. German and Italian Panavia Tornado IDS aircraft can also carry the B61. It is likely (although currently unconfirmed) that the F/A-22 Raptor and F-35 will be capable of employing the B61.
Approximately 150 are deployed with USAF units in Great Britain, Germany, and Turkey, and held in U.S. custody for use by NATO squadrons in Belgium, Germany, Italy, the Netherlands, and Turkey.
The B61 gravity bomb should not be confused with the MGM-1 Matador cruise missile, which originally was developed under the bomber designation B-61.
Design
The B61 is a variable-yield bomb designed for carriage by high-speed aircraft. It has a streamlined casing capable of withstanding supersonic flight speeds. The weapon is 11 ft 8 in (3.58 m) long, with a diameter of about 13 in (33 cm). Basic weight is about 700 lb (317.5 kg), although the weights of individual weapons may vary depending on version and fuse/retardation configuration.
The newest variant is the B61 Mod 11, a hardened penetration bomb with a reinforced casing (according to some sources, containing depleted uranium) and a delayed-action fuse, allowing it to penetrate fortified structures such as command posts before detonating. The Mod 11 is intended to replace the older, megaton-yield B53 bomb, a limited number of which have been retained for anti-fortification use.
Most versions of the B61 are equipped with a parachute retarder (currently a 24-ft (7.32 m) diameter nylon/Kevlar chute) to slow the weapon in its descent, giving the aircraft a chance to escape the blast (or to allow the weapon to survive impact with the ground in laydown mode). The B61 can be set for airburst , ground burst , or laydown detonation, and can be released at speeds up to Mach 2 and altitudes as low as 50 feet (15.24 m). Fusing for most versions is by radar.
The B61 is a variable-yield, kiloton-range weapon. Tactical versions (Mods 3, 4, and 10) can be set to 0.3, 1.5, 5, 10, 60, 80, or 170 kiloton explosive yield (depending on version). The strategic version (B61 Mod 7) has four yield options, with a maximum of 350 kilotons. The earth-penetrating Mod 11 apparently has a single, undisclosed yield. The early Mods have been retired, leaving the Mod 7, Mod 10, and Mod 11 as the only variants in active service.
