B61 nuclear bomb The B61 nuclear bomb is one of the primary thermonuclear weapon s in the U . S . Enduring Stockpile following the end of the Cold War . It is an intermediate yield strategic and tactical nuclear weapon featuring a two - stage radiation implosion design . The B61 is a variable yield bomb ( 0 . 3 to 340 kiloton yield in various versions and settings ) 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 fuze / retardation configuration . Development . 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 . Total production of all versions was approximately 3 , 155 , of which approximately 1 , 925 remain in service , and some 1 , 265 are considered to be operational . The warhead has changed little over the years , although early versions have been upgraded to improve the safety features . According to the journal " Physics Today " , September 2013 , page 45 , there are 200 B61 bombs actively in use by the United States . 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 B61 unguided 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 variety of U . S . military aircraft . Aircraft cleared for its use have included the 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 ; the F - 15 Eagle , 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 . The Lockheed S - 3 Viking was also able to deploy the B61 as a nuclear depth bomb . The B61 cannot fit inside the F - 22 Raptor ' s weapons bays and will instead be carried by the Lockheed Martin F - 35 Lightning II . Though exact numbers are hard to establish , research done by the Natural Resources Defense Council suggests approximately 180 are deployed with United States Air Force Europe units . , they are deployed in Europe under the NATO nuclear sharing arrangement . NATO has agreed to vastly improve the capabilities of this force with the increased accuracy of the B61 Mod . 12 upgrade and the stealthy delivery of the F - 35 . 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 ( 320 kg ) , although the weights of individual weapons may vary , depending on version and fuze / retardation configuration . B61 administrative procedures performed by ground - based personnel are executed 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 . On at least one design of B61 warhead the destructive yield of the bomb is adjusted via a dial marked " Option " , which allows 6 settings ranging from A to F . 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 . 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 . 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 . This offers the aircraft a chance to escape the blast , or allows 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 ) . 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 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 . intended to refurbish the B61 bombs under its Life Extension Program with the intention that the weapons should remain operational until at least 2025 . However , the United States Congress ordered that this work be stopped , pending reports from the National Academy of Sciences and JASON defense advisory panel . 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 . This version is designated Mod 12 . 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 . However , refitting the 400 weapons is now expected to cost over $ 10 billion . The B61 Mod 12 tail assembly contract was awarded to Boeing 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 .