B61 nuclear bomb

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B-61 bomb.jpg
B61 training unit intended for ground crew. It accurately replicates the shape and size of a "live" B61 (together with its safety/arming mechanisms) but contains only inert materials
TypeNuclear bomb
Service history
Used byUnited States
Production history
DesignerLos Alamos National Laboratory
ManufacturerPantex Plant
Produced1968 (full production)
No. built3,155
Weight700 pounds (320 kg)
Length11 feet 8 inches (3.56 m)
Diameter13 inches (33 cm)

Blast yieldBelieved to be either 0.3–340 kt[1] or 0.3-400 kt[2] in the weapon's various mods.

The B61 nuclear bomb is the primary thermonuclear gravity bomb in the United States Enduring Stockpile following the end of the Cold War. It is a low to intermediate-yield strategic and tactical nuclear weapon featuring a two-stage radiation implosion design.[3]

The B61 is of the variable yield ("dial-a-yield" in informal military jargon) design with a yield of 0.3 to 340 kilotons in its various mods. It has a streamlined casing capable of withstanding supersonic flight speeds. The weapon is 11 ft 8 in (3.56 m) long, with a diameter of about 13 inches (33 cm). Basic weight is about 700 pounds (320 kg), although the weights of individual weapons may vary depending on version and fuze/retardation configuration.


A B61 bomb undergoing disassembly.
B61 bomb casing; MAPS Air Museum, North Canton, Ohio.

The B61, 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. Shot Flintlock Halfbeak in June of 1966 may have been a full yield test of the weapon with other tests conducted between 1963 and 1968 at the Nevada Test Site.[4]

Total production of all versions was approximately 3,155, of which approximately 540 remain in active service, 415 in inactive service and 520 are awaiting dismantlement as of 2012.[5]

Nine versions 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 Russian Continuity of Government facility at Kosvinsky Kamen, finished in early 1996, was designed to resist US earth-penetrating warheads and serves a similar role as the American Cheyenne Mountain Complex.[6][7] The timing of the Kosvinsky completion date is regarded as one explanation for U.S. interest in a new nuclear bunker buster and the declaration of the deployment of the B-61 mod 11 in 1997: Kosvinsky is protected by about 1,000 feet (300 m) of granite.[8]

The B61 unguided bomb should not be confused with the MGM-1 Matador cruise missile, which was originally developed under the bomber designation B-61.


B61 bomb components. The nuclear physics package is contained in the silver cylinder centre-left

The B61 has been deployed by a variety of U.S. military aircraft. Aircraft cleared for its use have included the FB-111A, B-1 Lancer, B-2 Spirit, B-52 Stratofortress; F-101 Voodoo, F-100 D & F Super Sabre, F-104 Starfighter, F/A-18 Hornet, F-111 Aardvark and F-4 Phantom II fighter bombers; A-4 Skyhawk, A-6 Intruder and A-7 Corsair II attack aircraft; F-15E Strike Eagle and F-16 Falcon; British, German and Italian Panavia Tornado IDS aircraft. USAFE and all NATO dual role aircraft can carry B61s.

180 B61 bombs (in tactical variants) are deployed with NATO allies in Europe as part of the Nato Nuclear Weapons Sharing Program.[9] NATO has agreed to vastly improve the capabilities of this force with the increased accuracy of the B61 Mod 12 upgrade and the delivery of the stealthy F-35.[10][11] This will, for the first time, add a modest standoff capability to the B61.[12]

The B61 can fit inside the F-22 Raptor's weapons bays and will also be carried by the Lockheed Martin F-35 Lightning II.[13]


Inert training version of a B61 in an underground Weapons Storage and Security System (WS3) vault at Volkel Air Base, Netherlands. An access panel on the warhead is open, showing the interface for actions such as PAL (safety/arming) and variable yield setting
Internal nuclear components of the B61 bomb. The bomb was assembled at the Burlington AEC Plant and Pantex.

The B61 is a variable yield (formally known as FUFO or "full fuzing option", and "dial-a-yield" colloquially) dual use tactical and strategic bomb designed for external carriage by high-speed aircraft. It has a streamlined casing capable of withstanding supersonic flight speeds. The weapon is 11 feet 8 inches (3.56 m) long, with a diameter of about 13 inches (330 mm) and a basic weight of about 700 pounds (320 kg),[14] except for the Mod 11 version which has a weight of approximately 1,200 pounds (540 kg).[15]

The B61 is armed by ground-based personnel via an access panel located on the side of the bomb, which opens to reveal 9 dials, 2 sockets and a T-handle which manually triggers the "command disable" function. One of the sockets is a MC4142 "strike enable" plug which must be inserted in order to complete critical circuits in the safety/arming and firing mechanisms. The other socket is the PAL connector located in the top right hand corner of the arming panel, which has 23 pins marked with alphabetic letter codes.[16]

The B61 also features a "command disable" mechanism, which functions as follows: after entering the correct 3-digit numeric code it is then possible to turn a dial to "DI" and pull back a T-shaped handle which comes away in the user's hand. This action releases a spring-loaded firing pin which fires the percussion cap on an MC4246A thermal battery, powering it up. Electrical power from the thermal battery is sufficient to "fry" the internal circuitry of the bomb, destroying critical mechanisms without causing detonation. This makes the bomb incapable of being used. Any B61 which has had the command disable facility used must be returned to Pantex for repair.[16]

Thirteen versions of the weapon have reached the stage of being given a mod designation, nine have reached production and one is currently in development. Of those, four are retired (Mod 0, Mod 1, Mod 2, and Mod 5), one is in the inactive stockpile (Mod 10) and four are in the active stockpile (Mod 3, Mod 4, Mod 7 and Mod 11). The Mod 1, Mod 5 and Mod 7 are strategic versions of the weapon; the Mod 3, Mod 4 and Mod 10 are tactical versions of the weapon; and the Mod 11 and Mod 12 and dual use tactical and strategic weapons.[2]

The Mod 3 has a yield of 0.3, 1.5, 60 or 170 kt. The Mod 4 has a yield of 0.3, 1.5, 10 or 45 kt. The Mod 7 is thought to have a lower yield of 10 kt and an upper yield of 340 kt. The Mod 10 has a yield of 0.3, 5, 10 or 80 kt. Controversy exists to whether the Mod 11 has the same yield as the Mod 7 it was derived from or if it has a yield of 400 kt. The Mod 12 has a yield of 0.3, 5, 10 or 50 kt.[14][2][17]

The B61 can be set for airburst, parachute retarded airburst, ground burst, parachute retarded ground burst, or laydown detonation, and can be released at speeds up to Mach 2 and altitudes as low as 50 feet (15 m). In the weapon's laydown mode, it detonates 31 seconds after weapon release.[18] The Mod 0 to 10 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. This offers the aircraft a chance to escape the blast in its retarded modes, or allows the weapon to survive impact with the ground in laydown mode.

The B61 Mod 11 is the newest variant. A hardened penetration bomb with a reinforced casing and a delayed-action fuze, this allows the weapon to penetrate several metres into the ground before detonating, damaging fortified structures further underground. Developed from 1994, the Mod 11 went into service in 1997 replacing the older megaton-yield B53 bomb. 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.[15]

The U.S. intended to refurbish the B61 bombs under its Life Extension Program with the intention that the weapons should remain operational until at least 2025.[19]

In May 2010 the National Nuclear Security Administration asked Congress for $40 million to redesign the bomb to enable the Lockheed Martin F-35 Lightning II to carry the weapon internally by 2017.[20] This version is designated Mod 12.[21] The four hundred B61-12 bombs will be used by both tactical aircraft (such as the F-35) and strategic aircraft (such as the B-2) and the Tail Subassembly (TSA) will give them Joint Direct Attack Munition levels of accuracy, allowing the fifty kiloton warhead to have strategic effects from all carrying aircraft.[22] However, refitting the 400 weapons is now expected to cost over $10 billion.[23] The B61 Mod 12 tail assembly contract was awarded to Boeing on November 27, 2012 for $178 million.[24] Boeing will use their experience with the Joint Direct Attack Munition to yield JDAM-equivalent accuracy in a nuclear bomb.[25] This contract is only the first part of the billion dollar expense of producing and applying the tail kits, over and above the $10 billion cost to refurbish the warheads.[26] The B61-12 uses an internal guidance system and can glide to its target. On 1 July 2015, the National Nuclear Security Administration (NNSA) conducted the first of three flight tests of the B61-12 tail kit assembly.[27]


Mod Status Date Number produced Role Yields PAL type Notes
0 Retired 1968 to ?[14] 500[2] Cat B[4] First production weapons
1 Retired 1969 to ?[14] 700[2] Strategic Unknown to 340 kt None[4]
2 Retired 1975 to ?[4] 235[2] Cat D
3 Active 1979 to present[14] 545[2] Tactical 0.3, 1.5, 60 or 170 kt[14] Cat F
4 Active 1979 to present[14] 695[2] Tactical 0.3, 1.5, 10 or 45 kt[14] Cat F
5 Retired 1977 to ?[4] 265[2] Strategic ? to 340 kt Cat D
6 Never entered production ? ? Cat D Retrofit of Mod 0
7 Active 1985 to present[14] 600[2] Strategic 10, ? or 340 kt, allegedly 4 yield settings.[14] Cat D Retrofit of Mod 1
8 Never entered production ? Cat D Retrofit of Mod 2 and Mod 5
9 Never entered production ? Cat F Retrofit of Mod 0
10 Inactive stockpile 1990 to present[14] 215[2] Tactical 0.3, 5, 10 or 80 kt[14] Cat F Remanufactured from retired Pershing II W85 warheads.
11 Active 1997 to present 50[2] Tactical/Strategic Either 0.3, ? or 340 kt[14] or 400 kt[2] Cat F A retrofit of the Mod 7
12 In development 2019 onwards 400 to 500 weapons planned Tactical/Strategic[28][29][30] 0.3 to 50 kt[2] Cat F GPS guided, earth penetrating weapon

Mod 12[edit]

As of 2013, the Pentagon was asking for an $11 billion life-extension program for the B61 bomb, which would be the most ambitious and expensive nuclear warhead refurbishment in history. Congress is opposed to this effort for cost and timeline issues and questions for the B61's need. Cost estimates have doubled from $4 billion to $8 billion and production slipped from 2017 to 2020, then grew to $10 billion for life extension plus $1 billion for tail guidance kits and production was delayed to 2021.[citation needed] Sequestration budget cuts in early 2013 have delayed any start until 2020. The Senate Energy and Water Appropriations Subcommittee stated that extending the life of B61s and consolidating its variants may not be a cheap and low-risk method to meet military requirements.[citation needed]

The B61 Mod 12 is to replace the previous Mod 3, 4, 7, and 10 versions with 400–500 planned with a service life of 20 years. Refurbishing the existing variants and eliminating the guidance kit would save $2–3 billion.[citation needed] There are also questions about the future structure of gravity nuclear bombs[by whom?]. European deployments of warheads by NATO countries are cited as a reason for the low-yield Mod 12. With reductions planned of nuclear weapons in Europe, which may retire the older Mod 3 and 4 and the Mod 10 already slated for retirement, and the possibility that European nations may not build or procure new aircraft to carry the Mod 12 would eliminate the need for consolidation into a new type.[citation needed] Congressman John Garamendi has suggested that the B61 simply be retired and the B83 nuclear bomb be used instead.[citation needed]

While the B61 was first developed in the 1950s and 1960s, the B83 nuclear bomb entered service in 1983. The National Nuclear Security Administration, the Pentagon, and the Air Force have called the B83 a "relic of the Cold War" and believe that deploying a megaton-yield gravity bomb, the highest level nuclear weapon left in the U.S. inventory, to Europe is "inconceivable" at this point[citation needed]. The B61-12 is being pursued as a forward-deployed tactical nuclear weapon to protect NATO and Asian allies, and having a credible American nuclear deterrent may dissuade allies from developing their own nuclear weapons. The B61-12 can be deployed from dual-capable fighter aircraft, as well as planned to arm the F-35 and B-21 Raider.

The Air Force says that upgrading the B61 would be "considerably" less expensive than integrating the B83 to additional aircraft.[citation needed] Having a megaton yield that can't be as varied as the B61 also makes it less flexible and the Air Force is pushing for warheads that would have fewer collateral effects. Recapitalizing the B61 is hoped to lead to the retirement of the B83 to comply with plans for fewer, safer, and more reliable warheads.[citation needed] Retirement of the B83 would result in the elimination of the last megaton-yield U.S. bomb and leave the B61-series as the only U.S. gravity nuclear bomb.

The Pentagon and NNSA have stated that if B61 refurbishment does not begin by 2019, components in the existing weapons could begin to fail.[31][32] Tom Collina of the Arms Control Association has said that the new development could complicate arms control efforts with Russia.[33] In 2014 Congress slashed funding for the project and called for alternates to be studied.[34]

In January 2014, former Air Force Chief of Staff Norton A. Schwartz confirmed that the B61-12 nuclear bomb upgrade would have enhanced accuracy and a lower yield with less fallout compared to previous versions of the weapon.[citation needed] Accuracy has not been a guarantee for air-dropped nuclear weapons, so consequently large warheads were needed to effectively impact a target; the B61-11 nuclear earth-penetrator is accurate to 110–170 meters from the desired detonation location, so it requires a 400-kiloton warhead. The B61-12 is accurate to 30 meters from a target and only requires a 50-kiloton warhead.[citation needed] Schwartz believes that greater accuracy would both improve the weapon and create a different target set it can be useful against. An example is the higher-yield B61-11's role of attacking underground bunkers that need a ground burst to create a crater and destroy it through the shockwave. A 50-kiloton yield detonating on the ground produces a crater with a radius of 30–68 meters, depending on the density of the surface, effectively putting the bunker within the circular error probability.

Critics say that a more accurate and less destructive nuclear weapon would make leaders less cautious about deploying it, but Schwartz says it would deter adversaries more because the U.S. would be more willing to use it in situations where necessary.[citation needed] The B61-12 is also important for modernization of European nuclear stocks. The improved accuracy makes it more effective than the previous B61-3/4 currently deployed to the continent. F-16 and Panavia Tornado aircraft cannot interface with the new bomb due to electronic differences, but NATO countries that are buying the F-35 will be able to utilize it.[35] The first flight test for an inert B61-12 was conducted in 2015, with a second successful test in August 2017.[36][27]

In November 2015, a test of the B61-12 was conducted where the bomb penetrated underground, showing its potential as a nuclear earth-penetrator.[citation needed] Although ground penetration was not an objective of the Mod 12 upgrade, it could allow it to take up the penetrating mission of the B61-11, which has no life-extension planned and will expire in the 2030s.[citation needed] Being able to penetrate underground increases its effectiveness against buried targets, as it more efficiently transmits explosive energy through enhanced ground-shock coupling, allowing its max yield of 50 kilotons underground to have the equivalent surface-burst capability of a 750 kt to 1.25 megaton weapon. The B61-12's increased accuracy and earth-penetration capability allows a lower strike yield to be selected, reducing radioactive fallout risk, potentially making it more attractive to military planners.[37]

The B61-12 Life Extension Program continued in 2018 and on 29 June 2018 two successful non-nuclear system qualification flight tests at Tonopah Test Range were reported. [38]

See also[edit]

B61s on a bomb rack.


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External links[edit]