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 since October 25, 2011 after retirement of the B53. It was designed by Lawrence Livermore National Laboratory. History The B83 was based partly on the earlier B77 program, which was terminated because of cost overruns. The B77 was designed with an active altitude control and lifting parachute system for supersonic low-altitude delivery from the B-1A bomber. B77 nuclear component test firings were attributed to the Operation Anvil series in 1975 and 1976, specifically the "Cheese" test shots in Anvil: Anvil Kasseri – 28 October 1975, (B77/B83 full yield) Anvil Muenster – 3 January 1976, Anvil Fontina – 12 February 1976, Anvil Colby – 14 May 1976, The B83 nuclear components have been attributed as the same as the earlier B77. The B83 replaced several earlier weapons, including the B28, B43, and to some extent the ultra-high-yield B53. It was the first U.S. nuclear weapon designed from the start to avoid accidental detonation, with the use of "insensitive explosives" in the trigger lens system. Its layout is similar to that of the smaller B61, with the warhead mounted in the forward part of the weapon to make the bomb nose-heavy. It was intended for high-speed carriage (up to Mach 2.0) and delivery at high or low altitude. For the latter role, it is equipped with a parachute retardation system, with a Kevlar ribbon parachute capable of rapid deceleration. It can be employed in free-fall, retarded, contact, and laydown modes, for air-burst or ground-burst detonation. Security features include next-generation permissive action link (PAL) and a command disablement system (CDS), rendering the weapon tactically useless without a nuclear yield. The B83 was test fired in the Grenadier Tierra nuclear weapon test on 15 December 1984, at a reduced yield of 80 kilotonnes due to the Threshold Test Ban Treaty. With the dismantling of the last B53 bomb in 2011, the B83 became the highest yield nuclear weapon in the U.S. arsenal. In 2022, Biden administration declared that they plan to retire B83. Design The bomb is long, with a diameter of . The actual nuclear explosive package, judging from published drawings, occupies some in the forward part of the bomb case.