B61 Nuclear Weapon
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The B61
nuclear bomb A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear exp ...
is the primary
thermonuclear Nuclear fusion is a reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutron by-products. The difference in mass between the reactants and products is manifested as either the release or absorption of ener ...
gravity bomb An unguided bomb, also known as a free-fall bomb, gravity bomb, dumb bomb, or iron bomb, is an aircraft-dropped bomb (conventional or nuclear) that does not contain a guidance system and hence simply follows a ballistic trajectory. It includes ...
in the United States Enduring Stockpile following the end of the
Cold War The Cold War was a period of global Geopolitics, geopolitical rivalry between the United States (US) and the Soviet Union (USSR) and their respective allies, the capitalist Western Bloc and communist Eastern Bloc, which lasted from 1947 unt ...
. It is a low-to-intermediate yield
strategic Strategy (from Greek στρατηγία ''stratēgia'', "troop leadership; office of general, command, generalship") is a general plan to achieve one or more long-term or overall goals under conditions of uncertainty. In the sense of the "art o ...
and
tactical nuclear weapon A tactical nuclear weapon (TNW) or non-strategic nuclear weapon (NSNW) is a nuclear weapon that is designed to be used on a battlefield in military situations, mostly with friendly forces in proximity and perhaps even on contested friendly territ ...
featuring a two-stage
radiation implosion Radiation implosion is the compression of a target by the use of high levels of electromagnetic radiation. The major use for this technology is in fusion bombs and inertial confinement fusion research. History Radiation implosion was first deve ...
design. The B61 is of the
variable yield Variable yield, or dial-a-yield, is an option available on most modern nuclear weapons. It allows the operator to specify a weapon's yield, or explosive power, allowing a single design to be used in different situations. For example, the Mod-10 ...
("dial-a-yield" in informal military jargon) design with a yield of 0.3 to 340 kilotons in its various mods ("modifications"). It is a Full Fuzing Option (FUFO) weapon, meaning it is equipped with the full range of fuzing and delivery options, including air and ground burst fuzing, and free-fall, retarded free-fall and laydown delivery. It has a streamlined casing capable of withstanding supersonic flight and is long, with a diameter of about . The basic weight of the B-61 is about , although the weights of individual weapons may vary depending on version and
fuze In military munitions, a fuze (sometimes fuse) is the part of the device that initiates its function. In some applications, such as torpedoes, a fuze may be identified by function as the exploder. The relative complexity of even the earliest fu ...
/retardation configuration. As of 2020, the weapon was undergoing a 12th modification. According to the
Federation of American Scientists The Federation of American Scientists (FAS) is an American nonprofit global policy think tank with the stated intent of using science and scientific analysis to attempt to make the world more secure. FAS was founded in 1945 by a group of scient ...
in 2012, the roughly 400 B61-12s will each cost "more than its weight in gold" - $28 million apiece.


Development

In 1961 a report was issued indicating Navy and Air Force interest in a lightweight bomb to replace existing weapons, but that both services had considerably different military requirements for such a weapon. However, the authors of the report believed that due to advances in technology it was possible for a single weapon to fulfill both requirements. This was followed by a report from Sandia in mid-1962, that believed that a lightweight nuclear bomb with full fuzing option was possible and that such a program could be completed in a short time-span, possibly by 1965 or 1966. Development of the weapon that would become the B61 was authorized in December 1962. The justification for the program was that the new weapon would modernize the nuclear arsenal, improve the capability of aircraft and simplify the nuclear weapons inventory by replacing lower-yield versions of the B28 and
B43 nuclear bomb The B43 was a United States air-dropped variable yield thermonuclear weapon used by a wide variety of fighter bomber and bomber aircraft. The B43 was developed from 1956 by Los Alamos National Laboratory, entering production in 1959. It enter ...
s. The desired production date was June 1965. The weapon was designated the TX-61 in January 1963. Due to the short time-scales, it was decided to make maximum use of off-the-shelf components such as those developed for the
B57 nuclear bomb The B57 nuclear bomb was a tactical nuclear weapon developed by the United States during the Cold War. Development began at the Los Alamos National Laboratory in 1960 to meet a requirement for a multi-purpose weapon, suitable for use as a nuclear ...
. Environmental conditions specified included an indefinite temperature range of to , shocks of up to 40g, and in flight temperatures of up to for up to 40 minutes. Parachute deployment was specified to produce a maximum load of . The weapon was designed and built by the
Los Alamos National Laboratory Los Alamos National Laboratory (often shortened as Los Alamos and LANL) is one of the sixteen research and development Laboratory, laboratories of the United States Department of Energy National Laboratories, United States Department of Energy ...
in
New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...
. Production engineering began in 1965, with the first war-reserve B61-0 weapon accepted by the AEC in December 1966. However production was halted in May 1967 for design modifications to be made before resuming in January 1968. Shot Flintlock Halfbeak in June 1966 may have been a full yield test of the weapon with other tests conducted between 1963 and 1968 at the Nevada Test Site. During testing, spin motors were added to the weapon to produce a spin of 5 revolutions per second. This was to improve stability and decoupling during high speed delivery. Three alternatives to the weapon were also explored for still-classified reasons. The first alternative was halted due to its similarity to the original TX-61 design, and the Department of Defense was unfavorable to the second option which halted its exploration. The TX-61 design was ordered to "proceed along the lines" of the third alternative in May 1964, though it is unclear what that means. 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 . Thirteen versions of the B61 have been designed, known as Mod 0 through Mod 12. Of these, nine have entered production. Each shares the same
physics package Nuclear weapons design are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon to detonate. There are three existing basic design types: # Pure fission weapons are the simplest, least technically de ...
, with different yield options. One variant is the Mod 11, deployed in 1997, which is a ground-penetrating bunker busting weapon. The Russian
Continuity of Government Continuity of government (COG) is the principle of establishing defined procedures that allow a government to continue its essential operations in case of a catastrophic event such as nuclear war. Continuity of government was developed by the Br ...
facility at
Kosvinsky Kamen Mount Kosvinsky Kamen, Kosvinsky Mountain, Kosvinski Mountain, Kosvinsky Rock or Rostesnoy Rock () is a mountain in the northern Urals, Sverdlovsk Oblast, Russia.
, finished in early 1996, was designed to resist US earth-penetrating warheads and serves a similar role as the American
Cheyenne Mountain Complex The Cheyenne Mountain Complex is a United States Space Force installation and defensive bunker located in unincorporated El Paso County, Colorado, next to the city of Colorado Springs, at the Cheyenne Mountain Space Force Station, which host ...
. 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 Mod 11 in 1997: Kosvinsky is protected by about of
granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...
. The B61
unguided bomb An unguided bomb, also known as a free-fall bomb, gravity bomb, dumb bomb, or iron bomb, is an aircraft-dropped bomb (conventional or nuclear) that does not contain a guidance system and hence simply follows a ballistic trajectory. It includes ...
should not be confused with the
MGM-1 Matador The Martin MGM-1 Matador was the first operational surface-to-surface cruise missile designed and built by the United States. It was developed after World War II, drawing upon their wartime experience with creating the Republic-Ford JB-2, a ...
cruise missile A cruise missile is an unmanned self-propelled guided missile that sustains flight through aerodynamic lift for most of its flight path. Cruise missiles are designed to deliver a large payload over long distances with high precision. Modern cru ...
, which was originally developed under the bomber designation B-61.


Deployment

The B61 has been deployed by a variety of US military aircraft. US aircraft cleared for its use have included the
B-1 Lancer The Rockwell B-1 Lancer is a supersonic variable-sweep wing, heavy bomber used by the United States Air Force. It has been nicknamed the "Bone" (from "B-One"). , it is one of the United States Air Force's three strategic bombers, along with th ...
,
B-2 Spirit The Northrop B-2 Spirit, also known as the Stealth Bomber, is an American Heavy bomber, heavy strategic bomber, featuring low-observable stealth aircraft, stealth technology designed to penetrator (aircraft), penetrate dense anti-aircraft war ...
,
B-52 Stratofortress The Boeing B-52 Stratofortress is an American long-range, subsonic aircraft, subsonic, jet-powered strategic bomber. The B-52 was designed and built by Boeing, which has continued to provide support and upgrades. It has been operated by the ...
,
F/A-18 Hornet The McDonnell Douglas F/A-18 Hornet is an all-weather supersonic, twinjet, twin-engine, carrier-based aircraft, carrier-capable, Multirole combat aircraft, multirole combat aircraft, designed as both a Fighter aircraft, fighter and attack airc ...
,
A-6 Intruder The Grumman A-6 Intruder is a twinjet all-weather subsonic attack aircraft developed and manufactured by American aircraft company Grumman Aerospace. It was formerly operated by the U.S. Navy and U.S. Marine Corps. The A-6 was designed in ...
,
A-4 Skyhawk The Douglas A-4 Skyhawk is a single-seat subsonic carrier-capable light attack aircraft designed and produced by the American aerospace manufacturer Douglas Aircraft Company, and later, McDonnell Douglas. It was originally designated A4D und ...
,
F-111 The General Dynamics F-111 Aardvark is a retired supersonic, medium-range, multirole combat aircraft. Production models of the F-111 had roles that included attack (e.g. interdiction), strategic bombing (including nuclear weapons capabilit ...
,
F-15E Strike Eagle The McDonnell Douglas (now Boeing) F-15E Strike Eagle is an American all-weather multirole strike fighter derived from the McDonnell Douglas F-15 Eagle. Intended for the Dual-Role Fighter (DRF) program (initially called Enhanced Tactical Fi ...
and
F-16 Fighting Falcon The General Dynamics F-16 Fighting Falcon is an American single-engine supersonic Multirole combat aircraft, multirole fighter aircraft originally developed by General Dynamics for the United States Air Force (USAF). Designed as an air superio ...
and the F-35A. As part of NATO Nuclear Weapons Sharing,
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and
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Panavia Tornado The Panavia Tornado is a family of twin-engine, variable-sweep wing multi-role combat aircraft, jointly developed and manufactured by Italy, the United Kingdom and Germany. There are three primary #Variants, Tornado variants: the Tornado IDS ...
aircraft can also carry B61s. The B61 can fit inside the
F-22 Raptor The Lockheed Martin/Boeing F-22 Raptor is an American twin-engine, jet-powered, all-weather, supersonic stealth fighter aircraft. As a product of the United States Air Force's Advanced Tactical Fighter (ATF) program, the aircraft was de ...
's weapons bays. B61 tactical variants are deployed with NATO allies in Europe as part of the NATO Nuclear Weapons Sharing Program. About 150 bombs are stored at six bases: Kleine Brogel in Belgium,
Büchel Air Base Büchel Air Base is a military air base of the Luftwaffe in Büchel (Germany), near the city of Cochem and at about 70 km from Spangdahlem Air Base. It is home to the Taktisches Luftwaffengeschwader 33 (Tactical Air Force Wing 33; abbrevia ...
in Germany,
Aviano Aviano (; ) is a town and (municipality) in the Regional decentralization entity of Pordenone at the foot of the Dolomites mountain range in Friuli-Venezia Giulia, northeast Italy. Aviano is home to the C.R.O. (''Centro di Riferimento Oncologico ...
and Ghedi Air Base in Italy,
Volkel Air Base Volkel Air Base () is a military airbase used by the Royal Netherlands Air Force (RNLAF) - Dutch: ''Koninklijke Luchtmacht (KLu)'', located near the village of Volkel, Netherlands. Located in the north-east corner of the province of North Braban ...
in the Netherlands and Incirlik in Turkey. In 2012, NATO agreed to improve the capabilities of this force with the increased accuracy of the Mod 12 upgrade and the delivery of the F-35 aircraft. This added a modest standoff capability to the B61. The F-35A was certified to carry the B61-12 in October 2023, marking the first time an American fifth generation fighter has been certified as nuclear capable, and the first new platform in the NATO inventory to achieve such status since the early 1990s.


Design

The B61 is a
variable yield Variable yield, or dial-a-yield, is an option available on most modern nuclear weapons. It allows the operator to specify a weapon's yield, or explosive power, allowing a single design to be used in different situations. For example, the Mod-10 ...
("dial-a-yield" colloquially) dual use tactical and strategic bomb equipped with Full Fuzing Option (FUFO) designed for external carriage by high-speed aircraft. It has a streamlined casing capable of withstanding supersonic flight. The original B61-0 weapon was long, with a diameter of and a basic weight of with most later weapons having approximately the same dimensions and weight, except for the Mod 11 version which has a weight of approximately .


Ground operations

The B61 is armed by ground-based personnel via an access panel located on the side of the bomb, which opens to reveal nine dials, two sockets, and a T-handle which manually triggers the "command disable" function. One of the sockets is for 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 Phase Alternating Line (PAL) is a color encoding system for analog television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...
connector, which has 23 pins marked with alphabetic letter codes. The B61 "command disable" mechanism functions as follows: after entering the correct three-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 A firing pin or striker is a part of the firing mechanism of a firearm that impacts the primer in the base of a cartridge and causes it to fire. In firearms terminology, a striker is a particular type of firing pin where a compressed sprin ...
which fires the
percussion cap The percussion cap, percussion primer, or caplock, introduced in the early 1820s, is a type of single-use percussion ignition device for muzzle loader firearm locks enabling them to fire reliably in any weather condition. Its invention gave ...
on an MC4246A
thermal battery Thermal energy storage (TES) is the storage of thermal energy for later reuse. Employing widely different technologies, it allows surplus thermal energy to be stored for hours, days, or months. Scale both of storage and use vary from small t ...
, 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 activated must be returned to
Pantex Pantex is the primary United States nuclear weapons assembly and disassembly facility that aims to maintain the safety, security and reliability of the U.S. nuclear weapons stockpile. The facility is named for its location in the Panhandle of ...
for repair.


Fuzing and delivery

The B61 can be set for airburst or groundburst detonation, and by
free fall In classical mechanics, free fall is any motion of a physical object, body where gravity is the only force acting upon it. A freely falling object may not necessarily be falling down in the vertical direction. If the common definition of the word ...
, retarded free fall or
laydown delivery Laydown delivery is a mode of delivery found in some nuclear gravity bombs: the bomb's descent to the target is slowed by parachute so that it lands on the ground without detonating. The bomb then detonates by timer some time later. Laydown del ...
through the use of a
parachute A parachute is a device designed to slow an object's descent through an atmosphere by creating Drag (physics), drag or aerodynamic Lift (force), lift. It is primarily used to safely support people exiting aircraft at height, but also serves va ...
to slow down the weapon during release from the delivery aircraft. Only the Mod 0 to 10 versions of the B61 are equipped with a parachute retarder (currently a 24-ft (7.3 m) diameter
nylon Nylon is a family of synthetic polymers characterised by amide linkages, typically connecting aliphatic or Polyamide#Classification, semi-aromatic groups. Nylons are generally brownish in color and can possess a soft texture, with some varieti ...
/
Kevlar Kevlar (para-aramid) is a strong, heat-resistant synthetic fiber, related to other aramids such as Nomex and Technora. Developed by Stephanie Kwolek at DuPont in 1965, the high-strength material was first used commercially in the early 1970s as ...
chute). This offers the aircraft a chance to escape the blast in its retarded delivery modes, or allows the weapon to survive impact with the ground in laydown delivery mode.
Contact preclusion Contact preclusion is a fuze, fuzing feature found in some nuclear weapons in which backup contact fuzes in a nuclear weapon can be disabled when the weapon is set to air burst fuzing. When a nuclear attack is planned, the planner has the option o ...
can also be selected by the pilot. The weapon can be released at speeds up to Mach 2 and altitudes as low as . In one of the weapon's laydown modes, it detonates 31 seconds after weapon release. The Mod 11 is a hardened penetration bomb with a reinforced casing and a delayed-action
fuze In military munitions, a fuze (sometimes fuse) is the part of the device that initiates its function. In some applications, such as torpedoes, a fuze may be identified by function as the exploder. The relative complexity of even the earliest fu ...
; 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 Mod 11 is the
B-2 Spirit The Northrop B-2 Spirit, also known as the Stealth Bomber, is an American Heavy bomber, heavy strategic bomber, featuring low-observable stealth aircraft, stealth technology designed to penetrator (aircraft), penetrate dense anti-aircraft war ...
.


Variants

As of 2023, the B61 has 13 variants, referred to as Mod 0 through Mod 12.


B61 Mod 3 and 4

A Sandia document on the dates of the development phases of the US nuclear stockpile describes the B61-3 as an "improved Mod 2 w/IHE" and the B61-4 as "same as Mod 3 ex. Hi-Y". The B61 Mod 3 and 4 bombs do not contain
beryllium Beryllium is a chemical element; it has Symbol (chemistry), symbol Be and atomic number 4. It is a steel-gray, hard, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with ...
.


B61 Mod 5

A 1978 report on reducing or substituting beryllium in nuclear weapons noted that the B61-5 contained beryllium and that if the use of beryllium were to be restricted, the B61-5 could probably be replaced by the B61 Mod 3.


B61 Mod 6 and 8

The B61 Mod 6 and Mod 8 bombs were developed for use by the US Navy beginning in March 1987 and cancelled at the end of the Cold War. The weapons weighed , had a length of and a diameter of , and were one-point safe, used insensitive high explosives (IHE) in their primary stages and utilized enhanced electrical safety (EES). The weapons were to be built by converting existing B61-0, −2 and −5 weapons into Mod 6 and 8 weapons and the weapons were to use B61-7 weapon parts where possible. By mass, the largest deviations from the B61-7 were the Acorn assembly, MC4137 TSSG (trajectory sensing signal generator) and the JTA (described as "ballast for WR").


Electrical systems

The weapon's computer was the MC4139 Programmer, two of which are used on independent channels, and is identical to the programmer used on the B61-7. The MC3656 Main Battery is identical to the battery used on the B61-7 and is thermally operated, providing 120 seconds of power for the weapon, but initial power is supplied by the MC2238 Pulse Batteries which are activated by the weapon's pullout switches during separation from the aircraft. The weapon contained two neutron generators for initiation, using a 2400 volt 0.6 μF capacitor for neutron generator firing and a 3300 volt 2.0 μF capacitor for the firing set. If neither the radar fuze or the contact crystals actuated, the weapon would detonate at 120 seconds from arming. The weapons were to initially use the MC4175 Trajectory Sensing Signal Generators which are identical to the TSSG found in the B61-7, but starting from 1991, the Mod 6 was to get a new MC4137 Trajectory Sensing Signal Generator. The MC4175 stored the arming signal for the trajectory stronglink in its memory, so it featured a pair of
rolamite A Rolamite is a technology for very low friction bearings developed by Sandia National Laboratories in the 1960s. It consists of two cylindrical rollers held captive in a channel by an S-shaped metal strip. The strip is under tension, which keeps ...
acceleration switches designed to prevent the possibility of the signal being transferred to the stronglink before the rolamites were actuated by the spinning of the weapon in flight. The MC4137 instead is provided the unique signal from the MC4139 Programmer, which stores it in a volatile memory that erases after approximately seven seconds of lost power, meaning that without intent from the MC4139 and continuously applied power the MC4137 does not know how to arm the safelink.


Stronglink switches and weaklinks

The weapon was to feature a number of weapon stronglinks. Stronglinks are part of the weapon's safety systems and are designed to be robust enough that they can survive abnormal environments long enough for the weapon's weaklinks to fail. This requires weak and stronglinks to be colocated so they are exposed to the same environmental conditions in an accident. The first stronglink was the MC2969 Intent Stronglink Switch which was also used on the B61-3, −4 and −7, W78, W80 and B83 weapons. The MC2969 consisted of a 14-pin ceramic-insulated bank of switches that would close upon the receipt of the proper intent unique signal (IUQS) to its electromechanical decoder. Receipt of the wrong signal would lock the MC2969 in the open position until a specific unlock signal was received. The second stronglink was the MC2935 Trajectory Stronglink Switch of which there were two, one for each channel of the weapon's firing set. Like the MC2969, it mechanically locked if it received the wrong input signals, but unlike the MC2969 it could only be manually unlocked, which could only take place at the factory. Signals for the MC2935 come from either of the two MC4175s or the MC4137 Trajectory Sensing Signal Generators. A third stronglink existed inside the first exclusion region of the weapon and was involved in weapon arming. Details of the system are still classified.


B61 Mod 12

As of 2013 the Pentagon saw the
B83 nuclear bomb The B83 is a variable-yield thermonuclear gravity bomb developed by the United States in the late 1970s that entered service in 1983. With a maximum yield of , it has been the most powerful nuclear weapon in the United States nuclear arsenal ...
as a "relic of the Cold War," believing that deploying a megaton-yield gravity bomb, the highest level nuclear weapon left in the U.S. inventory, to Europe was "inconceivable" at this point. It can also only be carried by the B-2 bomber, and integrating it onto additional aircraft would be costly. The Mod 12 upgrade is being pursued as a forward-deployed tactical/strategic nuclear weapon to protect NATO and Asian allies since it can be used from dual-capable fighter aircraft, as well as planned to arm the F-35 and B-21 Raider, and its lower yield options make it more flexible with less collateral effects. Recapitalizing the B61 is hoped to lead to the retirement of the B83, resulting in the elimination of the last megaton-yield U.S. bomb and leave the B61-series as the only U.S. gravity nuclear bomb. In 2013, the Pentagon and NNSA stated that if B61 refurbishment did not begin by 2019, components in the existing weapons could begin to fail. In 2013 Tom Collina of the
Arms Control Association The Arms Control Association is a United States–based nonpartisan membership organization founded in 1971, with the self-stated mission of "promoting public understanding of and support for effective arms control policies." The group publishes ...
said that the new development could complicate arms control efforts with Russia. In 2014, Congress slashed funding for the project and called for alternates to be studied. In January 2014, former Air Force Chief of Staff
Norton A. Schwartz Norton Allan Schwartz (born 14 December 1951) is a retired United States Air Force general who served as the 19th Chief of Staff of the Air Force from 12 August 2008, until his retirement in 2012. He previously served as commander, United State ...
stated that the Mod 12 nuclear bomb upgrade would have enhanced accuracy and a lower yield with less fallout compared to previous versions of the weapon. Accuracy has not been a guarantee for air-dropped nuclear weapons, so consequently large warheads were needed to effectively impact a target; the Mod 11 nuclear earth-penetrator is accurate to 110–170 meters from the desired detonation location, so it requires a 400-kiloton warhead. The Mod 12 is accurate to 30 meters from a target and only requires a 50-kiloton warhead. 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 Mod 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 Circular error probable (CEP),Circular Error Probable (CEP), Air Force Operational Test and Evaluation Center Technical Paper 6, Ver 2, July 1987, p. 1 also circular error probability or circle of equal probability, is a measure of a weapon s ...
. In 2014 critics said that a more accurate and less destructive nuclear weapon would make leaders less cautious about deploying it, while Schwartz said it would deter adversaries more because the U.S. would be more willing to use it in situations where necessary. The improved accuracy would make it more effective than the previous Mod 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 buying the F-35 would be able to utilize it. The first flight test for an inert Mod 12 was conducted in 2015, with a second successful test in August 2017. Despite claims the Mod 12 has an earth penetrating capability, the weapon does not have the reinforced structure like that of the Mod 11, which is required to function as an earth penetrating weapon. The Mod 11 will be retained in service for the ground penetrating mission. The Mod 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. In October 2018, the Mod 12 guided tail-kit assembly received Milestone C approval to enter the production phase; the TKA went through the traditional test program in under 11 months, achieving a 100% success rate for all 31 bomb drops. The B61-12 nuclear bomb completed its successful flight tests with the US Air Force's F-15E in June 2020. It was dropped from above 25,000ft and was in the air for approximately 55 seconds before hitting the target. The first B61-12 bomb was produced in November 2021. The weapon replaces the B61 mod 3, mod 4 and mod 7 bombs while the B61-11 will be retained in the stockpile. It is expected that the LEP will extend the B61's life by at least 20 years. In October 2022, it was announced that the US military planned to accelerate the deployment of the Mod 12 in Europe. This drew criticism from the Russian Deputy Minister of Foreign Affairs Alexander Grushko, who accused the US government of "reducing the nuclear threshold" with the weapon's increased accuracy. The
F/A-18E/F Super Hornet The Boeing F/A-18E and F/A-18F Super Hornet are a series of American supersonic twinjet, twin-engine, Carrier-based aircraft, carrier-capable, Multirole combat aircraft, multirole fighter aircraft derived from the McDonnell Douglas F/A-18 Ho ...
is not listed as a future platform.


B61 Mod 13

Initially, the NNSA Stockpile Stewardship and Management Plan anticipated Phase 1 development for the B61 Mod 13 Life Extension Program (LEP) beginning in 2037 with first production of the weapon in 2050, but in 2023 plans were announced to produce a new gravity bomb similar to that of the B61-12, but having a high yield similar to that of the B61-7, named the B61 Mod 13. This discards plans for the Mod 13 to be a future Mod 12 LEP. It is planned that for each B61-13 produced, one fewer B61-12 is to be produced, therefore not increasing the planned number of new B61 bombs; defense officials indicated only "a few dozen" B61-13s may be produced. The new bomb will be carried by the B-21 Raider, but it is not planned to be deployed on the F-35. The
Federation of American Scientists The Federation of American Scientists (FAS) is an American nonprofit global policy think tank with the stated intent of using science and scientific analysis to attempt to make the world more secure. FAS was founded in 1945 by a group of scient ...
have accused the weapon of being a "political bomb", introduced to finally retire the B83-1 nuclear bomb, whose retirement has been blocked by hardliners. The first B61-13 was completed in May 2025.


W61 Earth Penetrator Warhead

A W61 Earth Penetrator Warhead (EPW) with a yield of was developed for the AGM-129 Advanced Cruise Missile and the
MGM-134 Midgetman The MGM-134A Midgetman, also known as the Small Intercontinental Ballistic Missile, was an intercontinental ballistic missile developed by the United States Air Force. The system was mobile and could be set up rapidly, allowing it to move to a ne ...
small ICBM. The weapon entered Phase 1 initial development in January 1985 and phase 4 production engineering in September 1992 before being cancelled in December of that year. In the Advanced Cruise Missile role, the weapon was to replace aging B53 bombs, but after the W61 cancellation the role was filled by the B61-11 bomb.


Pits

A declassified technical report on the automation of pit handling at
Pantex Pantex is the primary United States nuclear weapons assembly and disassembly facility that aims to maintain the safety, security and reliability of the U.S. nuclear weapons stockpile. The facility is named for its location in the Panhandle of ...
indicates that the B61-2 and B61-5 share a common pit design, as do the B61-3, B61-10 and W85. The B61-0 and B61-4 do not share a pit with any other weapon. As the B61-7 was a retrofit of the B61-1 and the B61-11 was a retrofit of the B61-7, they presumably share a common pit.


Cost

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 The Lockheed Martin F-35 Lightning II is an American family of single-seat, single-engine, supersonic Stealth aircraft, stealth strike fighters. A multirole combat aircraft designed for both Air superiority fighter, air superiority and att ...
to carry the weapon internally by 2017. This version is designated Mod 12. The four hundred Mod 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 The Joint Direct Attack Munition (JDAM) is a guidance kit that converts unguided bombs, or "dumb bombs", into all-weather precision-guided munitions (PGMs). JDAM-equipped bombs are guided by an integrated inertial guidance system coupled to a G ...
levels of accuracy, allowing the fifty kiloton warhead to have strategic effects from all carrying aircraft. However, refitting the 400 weapons is now expected to cost over $10 billion. The Mod 12 tail assembly contract was awarded to
Boeing The Boeing Company, or simply Boeing (), is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, and missiles worldwide. The company also provides leasing and product support s ...
on November 27, 2012 for $178 million. Boeing will use their experience with the Joint Direct Attack Munition to yield JDAM-equivalent accuracy in a nuclear bomb. 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.Kristensen, Hans.
"$1 Billion for a Nuclear Bomb Tail."
''FAS'', 12 April 2013.
The Mod 12 uses an internal guidance system and can glide to its target. On 1 July 2015, the
National Nuclear Security Administration The National Nuclear Security Administration (NNSA) is a United States federal agency responsible for safeguarding national security through the military application of nuclear science. NNSA maintains and enhances the safety, security, and ef ...
(NNSA) conducted the first of three flight tests of the Mod 12 tail kit assembly. According to the
Federation of American Scientists The Federation of American Scientists (FAS) is an American nonprofit global policy think tank with the stated intent of using science and scientific analysis to attempt to make the world more secure. FAS was founded in 1945 by a group of scient ...
in 2012, the roughly 400 B61-12s will cost $28 million each.


See also

*
B61 Family The B61 Family is a series of nuclear weapons based on the B61 nuclear bomb. B61 nuclear bomb Initial development The B61 bomb was developed by Los Alamos Scientific Laboratory (LASL; now Los Alamos National Laboratory) starting in 1960. The inte ...
*
List of nuclear weapons This is a list of nuclear weapons listed according to country of origin, and then by type within the states. The United States, Russia, China and India are known to possess a nuclear triad, being capable to deliver nuclear weapons by land, sea a ...
* WE.177 *
Weapons Storage and Security System Weapons Storage and Security System (WS3) is a system including electronic controls and vaults built into the floors of Protective Aircraft Shelters (PAS) on several NATO military airfields all over the world. These vaults are used for safe sp ...


Notes


References


External links

* . * . * . * , an anti-nuclear weapons organization * . * . * . {{USAF equipment Nuclear bombs of the United States Tactical nuclear weapons Military equipment introduced in the 1960s