B53 nuclear bomb The Mk / B53 was a high - yield bunker buster thermonuclear weapon developed by the United States during the Cold War . Deployed on Strategic Air Command bombers , the B53 , with a yield of , was the most powerful weapon in the U . S . nuclear arsenal after the last B41 nuclear bomb s were retired in 1976 . The B53 was the basis of the W - 53 warhead carried by the Titan II Missile , which was decommissioned in 1987 . Although not in active service for many years before 2010 , fifty B53s were retained during that time as part of the " Hedge " portion of the Enduring Stockpile until its complete dismantling in 2011 . The last B53 was disassembled on October 25 , 2011 , a year ahead of schedule . With its retirement , the largest bomb currently in service in the U . S . nuclear arsenal is the B83 , with a maximum yield of . The B53 was replaced in the bunker - busting role by a variant of the two - stage B61 nuclear bomb . History . Development of the weapon began in 1955 by Los Alamos National Laboratory , based on the earlier Mk 21 and Mk 46 weapons . In March 1958 the Strategic Air Command issued a request for a new Class C ( less than five tons , megaton - range ) bomb to replace the earlier Mk 41 . A revised version of the Mk 46 became the TX - 53 in 1959 . The development TX - 53 warhead was apparently never tested , although an experimental TX - 46 predecessor design was detonated 28 June 1958 as Hardtack Oak , which detonated at a yield of 8 . 9 Megatons . The Mk 53 entered production in 1962 and was built through June 1965 . About 340 bombs were built . It entered service aboard B - 47 Stratojet , B - 52G Stratofortress , and B - 58 Hustler bomber aircraft in the mid - 1960s . From 1968 it was redesignated B53 . Some early versions of the bomb were dismantled beginning in 1967 . About 50 bomb and 54 Titan warhead versions were in service through 1980 . After the Titan II program ended , the remaining W - 53s were retired in the late 1980s . The B53 was also intended to be retired in the 1980s , but 50 units remained in the active stockpile until the deployment of the B61 - 11 in 1997 . At that point the obsolete B53s were slated for immediate disassembly ; however , the process of disassembling the units was greatly hampered by safety concerns as well as a lack of resources . In 2010 authorization was given to disassemble the 50 bombs at the Pantex plant in Texas . The process of dismantling the last remaining B53 bomb in the stockpile commenced on October 25 , 2011 and was completed soon afterwards . Specifications . The B53 was long with a diameter of . It weighed , including the parachute system and the honeycomb aluminum nose cone to enable the bomb to survive laydown delivery . It had five parachutes : one pilot chute , one extractor chute , and three main chutes . Chute deployment depends on delivery mode , with the main chutes used only for laydown delivery . For free - fall delivery , the entire system was jettisoned . The warhead of the B53 used oralloy ( highly enriched uranium ) instead of plutonium for fission , with a mix of lithium - 6 deuteride fuel for fusion . The explosive lens comprised a mixture of RDX and TNT , which was not insensitive . Two variants were made : the B53 - Y1 , a " dirty " weapon using a U - 238 - encased secondary , and the B53 - Y2 " clean " version with a non - fissile ( lead or tungsten ) secondary casing . Explosive yield was approximately nine megatons . Role . It was intended as a bunker buster weapon , using a surface blast after laydown deployment to transmit a shock wave through the earth to collapse its target . Attacks against the Soviet deep underground leadership shelters in the Chekhov / Sharapovo area south of Moscow envisaged multiple B53 / W53 exploding at ground level . It has since been supplanted in such roles by the earth - penetrating B61 Mod 11 , a bomb that penetrates the surface to deliver much more of its explosive energy into the ground , and therefore needs a much smaller yield to produce the same effects . The B53 was intended to be retired in the 1980s , but 50 units remained in the active stockpile until the deployment of the B61 - 11 in 1997 . At that point the obsolete B53s were slated for immediate disassembly ; however , the process of disassembling the units was greatly hampered by safety concerns as well as a lack of resources . The last remaining B53 bomb began the disassembly processes on Tuesday , 25 October 2011 at the Energy Department ’ s Pantex Plant . W53 . The W53 warhead of the Titan II ICBM used the same physics package as the B53 , without the air drop - specific components like the parachute system , reducing its mass to about . The 8 , 140 pound Mark - 6 re - entry vehicle containing the W53 warhead was about 123 inches ( 3 . 1 meters ) long , 7 . 5 feet ( 2 . 2 meters ) in diameter and was mounted atop a spacer which was 8 . 3 feet ( 2 . 5 meters ) in diameter at the missile interface ( compared to the missile ' s core diameter of 10 feet ) . With a yield of 9 Megatons , it was the highest yield warhead ever deployed on a US missile . About 65 W53 warheads were constructed between December 1962 and December 1963 . On September 19 , 1980 a fuel leak caused a Titan II to explode within its silo in Arkansas , throwing the W53 warhead some distance away . Due to the safety measures built into the weapon , it did not explode or release any radioactive material . 52 active missiles were deployed in silos prior to the beginning of the retirement program in October 1982 . With the retirement of the Titan fleet , disassembly of the W53 warheads was completed by about 1988 . Effects . Assuming a detonation at optimum height , a 9 megaton blast would result in a fireball with an approximate diameter . The radiated heat would be sufficient to cause lethal burns to any unprotected person within a radius ( ) . Blast effects would be sufficient to collapse most residential and industrial structures within a radius ( ) ; within virtually all above - ground structures would be destroyed and blast effects would inflict near 100 % fatalities . Within a 500 rem dose of ionizing radiation would be received by the average person , sufficient to cause a 50 % to 90 % casualty rate independent of thermal or blast effects at this distance .