W41 (nuclear weapon)

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For technical reasons, this article heading is W41 for a device actually designated B41

B41 nuclear bombs were the highest-yielding nuclear weapons ever deployed by the United States. A gravity bomb carried by the B-52 bomber, it came in two versions:

  • B41Y1: "dirty" high-fallout with a yield of 25 Mt[note 1]
  • B41Y2: "clean" less than 10 Mt yield.

It is unclear if the Soviets ever deployed a weapon in this range; their 58-megaton[note 1] "Tsar Bomba", which is generally believed to be the Primary and Secondary only for a 100-megaton device, was experimental although sufficiently weaponized to be dropped from a modified bomber. Only the Soviets and Americans ever tested devices with greater than 10 Mt yield.


The B41Y1 was the only three-stage device (see fusion device) ever built by the United States. As opposed to the usual fission Primary and fusion Secondary of a Teller-Ulam design, this bomb's uranium tamper constituted a Tertiary.[1] The Y2 version lacked the Tertiary.

In the Y2 version, the device had the highest weight-to-yield ratio of any United States nuclear weapon. Carey Sublette quoted Theodore Taylor as saying the maximum practical ratio was 6.0 kt yield per kilogram of nuclear weapon; the deployed weapon, with parachutes and other weight that was not part of the ratio calculation, was 10,670 pound (4,840 kg). Test devices from which the B-41 was weaponized, however, were in the 9,100 pound (4,128 kg) range, consistent with Taylor's estimate.[2]


Approximately 500 were built, between September 1960 and June 1962, and were in service from November 1963 to July 1976. It was replaced by the 9 Mt B53, which also was implemented as the W53 warhead for the UGM-27 Titan II intercontinental ballistic missile.[2]


  1. 1.0 1.1 The energy yields of nuclear weapons are commonly expressed in units of TNT equivalent, meaning the energy yield from the explosion of a stated amount of trinitrotoluene (TNT). The commonly used units are a kilotonne or a megatonne of TNT equivalent. A kilotonne (kt) of TNT equivalent is equal to 1012 joules and a megatonne (Mt) of TNT equivalent is equal to 1015 joules. The kilotonne and megatonne are often taken to be synonymous with kiloton and megaton.


  1. Globalsecurity.org, B-41
  2. 2.0 2.1 Sublette, Carey, "The B-41 (Mk-41) Bomb: High yield strategic thermonuclear bomb", Nuclear Weapon Archive