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. Specifications The B53 was long with a diameter of . It weighed , including the W53 warhead, 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 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. In 1988, some B53s were upgraded to the B53 Mod 1 (B53-1) variant to improve weapon safety and to provide compatibility with the G/H variants of the B52 bomber. During this upgrade the weapon lost full-fuzing capability, Retaining only the laydown fuzing mode. The B53-1 had a selectable laydown time of 30 to 240 seconds in 30 second increments. 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,