B61 bomb in various stages of assembly.

The B61 nuclear bomb is the primary thermonuclear weapon in the U.S. Enduring Stockpile following the end of the Cold War.

Development

A B61 bomb undergoing disassembly.

The B61, originally known (before 1968) as the TX-61, was designed in 1963. It was designed and built by the Los Alamos National Laboratory in New Mexico. It began from a program for a lightweight, streamlined weapon launched in 1961. Production engineering began in 1965, with full production beginning in 1968 following a series of development problems.

Total production of all versions was approximately 3,155, of which approximately 1,925 remain in service as of 2002, and some 1,265 are considered to be operational.^{[citation needed]} The warhead has changed little over the years, although early versions have been upgraded to improve the safety features.^{[citation needed]}

Nine versions (or 'Mods') of the B61 have been produced. Each shares the same 'physics package,' with different yield options.

The newest variant is the B61 Mod 11, deployed in 1997, which is a ground-penetrating bunker buster.

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.

When the B61 was still classified, aircrew were not allowed to use the term "B61". Instead, it was referred to as a "shape", "silver bullet", or even "external delivery".

Deployment

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 Fighting Falcon, F/A-18 Hornet and Super Hornet; and the Lockheed S-3 Viking. British, German and Italian Panavia Tornado IDS aircraft can also carry the B61.

Though exact numbers are hard to establish, research done by the Natural Resources Defense Council suggests approximately 480 are deployed with United States Air Force units in various European countries.^[1]

Design

Internal nuclear components of the B61 bomb.

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 (320 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 fuze, allowing it to penetrate several metres into the ground before detonating, damaging fortified structures further underground [1]. The Mod 11 weighs about 1,200 lb (540 kg). Developed from 1994, the Mod 11 went into service in 1997 replacing the older megaton-yield B53 bomb, a limited number of which had been retained for anti-fortification use. About 50 Mod 11 bombs have been produced, their warheads converted from Mod 7 bombs. At present, the primary carrier for the B61 Mod 11 is the B-2 Spirit.

Most versions of the B61 are equipped with a parachute retarder (currently a 24-ft (7.3 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 m). Fusing for most versions is by radar.

The B61 is a variable-yield, kiloton-range weapon called "Full Fuzing Option"(FUFO) or "Dial-a-yield" by many service personnel. 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 340 kilotons. Sources conflict on the yield of the earth-penetrating Mod 11; the physics package or bomb core components of the Mod 11 are apparently unchanged from the earlier strategic Mod 7, however the declassified 2001 Nuclear Posture Review [2] states that the B-61-11 has only a single yield; some sources indicate 10 KT, others suggest the 340 kiloton maximum yield as the Mod-7.

The early Mods 0, 1, 2, and 5 have been retired (Mods 6, 8, and 9 were cancelled before production), and the Mod 10 has been moved to the inactive stockpile, leaving the Mods 3, 4, 7, and 11 as the only variants in active service.

The U.S. is refurbishing the B61 bombs under its Life Extension Program with the intention that the weapons should remain operational until at least 2025.^[2]

See also

B61s on a bomb rack.

• List of nuclear weapons
• B61 Family

References

External links

• "Developing and Producing the B-61", official AEC film
• B61 information at Carey Sublette's NuclearWeaponArchive.org
• B61 information at GlobalSecurity.org
• B61-11 Concerns and Background from the Los Alamos Study Group, an anti-nuclear weapons organization
• Low-Yield Earth-Penetrating Nuclear Weapons by Robert W. Nelson, Federation of American Scientists, January/February 2001, Volume 54, Number 1