W80 (nuclear warhead)
The W80 is a low to intermediate yield two-stage thermonuclear warhead deployed by the U.S. enduring stockpile with a variable yield of of TNT.
It was designed for deployment on cruise missiles and is the warhead used in all nuclear-armed ALCM and ACM missiles deployed by the US Air Force, and in the US Navy's BGM-109 Tomahawk. It is essentially a modification of the widely deployed B61 weapon, which forms the basis of most of the current US stockpile of nuclear gravity bombs. The very similar W84 warhead was deployed on the retired BGM-109G Ground Launched Cruise Missile.
Dimensions
The W80 is physically quite small: the physics package itself is about the size of a conventional Mk.81 bomb, in diameter and long, and only slightly heavier at about.Armorers have the ability to select the yield of the resulting explosion in-flight, a capability referred to as variable yield, colloquially referred to as "dial-a-yield". The minimum yield, perhaps using just the boosted fission primary, is around 5 kilotons of TNT; the highest yield is equivalent to around.
History
Early development
The Los Alamos National Laboratory began development on the W80 in June 1976, with the brief of producing a custom weapon for the cruise missiles then under construction. With "the basic design" being derived from the B61. The main design differences are presumably a smaller secondary producing only 150 kt yield and simplification of the design giving the weapon only two yield settings; 5 and 150 kt.Production of the W80 mod 1 to arm the ALCM started in January 1979, and a number of warheads had been completed by January 1981 when the first low-temperature test was carried out. To everyone's surprise the test delivered a much lower yield than was expected, apparently due to problems in the TATB based insensitive high explosives used to fire the primary. This problem turned out to affect several models of the B61-based line, and production of all weapons was suspended while a solution was worked on. Production restarted in February 1982.
In March 1982, designers began working on a W80 variant intended for the Navy's Tomahawk program. The W80 mod 0 used "supergrade" fission fuel, which has less radioactivity, in the primary in place of the conventional plutonium used in the Air Force's version. "Supergrade" is industry parlance for plutonium alloy bearing an exceptionally high fraction of Pu-239, leaving a very low amount of Pu-240 which is a gamma emitter in addition to being a high spontaneous fission isotope. Such plutonium is produced from fuel rods that have been irradiated a very short time as measured in MW-Day/Ton burnup. Such low irradiation times limit the amount of additional neutron capture and therefore buildup of alternate isotope products such as Pu-240 in the rod, and also by consequence is considerably more expensive to produce, needing far more rods irradiated and processed for a given amount of plutonium. Submarine crew members routinely operate in proximity to stored weapons in torpedo rooms, in contrast to the air force where exposure to warheads is relatively brief. The first models were delivered in December 1983 and the Mod 0 went into full production in March 1984.
Production of the W80 was completed by September 1990, although the exact date at which the respective Mod 0 and Mod 1 runs ended is not clear. A total of 1750 Mod 1 and 367 Mod 0 devices were delivered; 1,000 Mod 1 devices were deployed on the original ALCM, another 400 on the later ACM, and 350 Mod 0s on the Tomahawk.
Some of the original ALCMs would later have their mod 1 warheads removed and instead be fitted with conventional warheads producing the CALCM conversion. Under START II only 400 ACMs would have retained their nuclear warheads, and the rest would have been converted to CALCMs and their warheads removed to the inactive stockpile.
2007 nuclear weapons incident
On August 30, 2007, six cruise missiles armed with W80-1 warheads were mistakenly loaded onto a B-52 and flown from Minot Air Force Base, North Dakota, to Barksdale Air Force Base, Louisiana, on a mission to transport cruise missiles for decommissioning. It was not discovered that the six missiles had nuclear warheads until the plane landed at Barksdale, leaving the warheads unaccounted for over 36 hours. This was the first time since 1968 that nuclear warheads were publicly revealed to have been transported on a US bomber. The munitions crews involved in mistakenly loading the nuclear warheads at Minot were temporarily decertified from performing their duties involving nuclear munitions.W80-4 Refurbishment and LRSO
In 2014 a life extension program for the W80-1 was started and the LEP warhead was given the W80-4 designation. The warhead will be used on the ALCM and a new LRSO cruise missile. First production unit is estimated in 2025 and production should finish in 2031. According to public descriptions of the program, the warhead will offer no increased military capability, only refurbishing and updating components, and increasing weapon safety and reliability.Mods
| Mod | Status | Date | Number produced | Yields | PAL type | Notes |
| 0 | Inactive stockpile | 1984 to approx 2011 | 367 | 5 or 150 kt | Cat D | Warhead for BGM-109A Tomahawk TLAM-N missile. Warhead uses supergrade plutonium due to weapon's proximity to crew. |
| 1 | In service | September 1981 to present | 1750 | 5 or 150 kt | Cat D | First production units. Warhead for AGM-86 ALCM and AGM-129 ACM cruise missiles. |
| 2 | Never entered production | 0 | Cat D | Life extension program for W80-0, cancelled in 2006 | ||
| 3 | Never entered production | 0 | Cat D | Life extension program for W80-1, cancelled in 2006 | ||
| 4 | In development | 2025 onwards | More than 500 planned | Unknown | Unknown | Life extension program for W80-1. Warhead will be used on new Long Range Stand Off Weapon cruise missile currently under development. |