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B53 nuclear bomb

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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 9 megatons, was the most powerful weapon in the U.S. nuclear arsenal after the last B41 nuclear bombs 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 25 October 2011, a year ahead of schedule.

With its retirement, the largest bomb in service in the U.S. nuclear arsenal is the B83, with a maximum yield of 1.2 megatons. The B53 was replaced in the bunker-busting role by the B61 Mod 11.

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. After the Titan II program ended, the remaining W-53s were retired in the late 1980s. The B53 was retired in 1986, but in 1988 50 units were brought back into service and received the B53 Mod 1 safety upgrade so the air force could cover certain targets previously covered by Titan II. These weapons 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 was completed in 2011.

The B53 was 12 feet 4 inches (3.76 m) long with a diameter of 50 inches (4.17 ft; 1.27 m). It weighed 8,850 pounds (4,010 kg), including the W53 warhead, the 800-to-900 lb (360-to-410 kg) parachute system and the honeycomb aluminum nose cone to enable the bomb to survive laydown delivery. It had five parachutes: one 5-foot (1.52 m) pilot chute, one 16-foot (4.88 m) extractor chute, and three 48-foot (14.63 m) 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 W53 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. The explosive yield for the Y1 version was declassified in 2014 as being 9 Mt.

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