B41 nuclear bomb

The B-41 (also known as Mk-41) was a thermonuclear weapon deployed by the United States Strategic Air Command in the early 1960s. It was the most powerful nuclear bomb ever developed by the United States, with a maximum yield of 25 megatons. The B-41 was the only three-stage thermonuclear weapon fielded by the U.S.

The development of the B-41 began in 1955 with a USAF requirement for a Class B (high-yield, over 10,000 lb or 4,500 kg) weapon. It was based on the "Fagotti (bassoon)" test device first fired in the Redwing Zuni test of 27 May 1956. An ICBM warhead version of the weapon was cancelled in 1957 while still in the design stage.

The B-41 was the only three-stage thermonuclear weapon fielded by the U.S. It had a deuterium-tritium boosted primary, probably with lithium-6-enriched deuteride fuel for the fusion reaction in the secondary stage. This was followed by a yet-larger third fusion stage, the tertiary stage, compressed by the secondary stage. Finally, there was a fission jacket.

Two versions were deployed, Y1, a "dirty" version with a tertiary stage encased with U-238 (natural uranium), and Y2, a "clean" version with a lead-encased tertiary. It was the highest-yield nuclear weapon ever deployed by the United States, with a maximum yield of 25 megatons (Mt), and weighing in at 4,850 kg (10,690 lb). It remains the highest yield-to-weight ratio of any weapon created. The US claimed in 1963 that it could produce a 35 Mt fusion bomb, and put it on a Titan II (3,700 kg [8,200 lb] payload), almost doubling the yield-to-weight ratio of the B-41.

The B-41 was of the usual long cylindrical shape. The nuclear fusion warhead was of the Teller-Ulam type and used a 40–100 kiloton implosion type nuclear fission primary (reportedly based on the Smokey TX-41 shot of Operation Plumbbob) fueled by HEU to trigger the lithium-6 deuteride fusion fuel. Between 500 and 1,000 kg (1,100 and 2,200 lb) of lithium deuteride was used and, in the Y1 version, the third ("tertiary") stage was enclosed in a uranium tamper.

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