The W85 was a thermonuclear warhead developed by the United States of America to arm the Pershing II missile. It had a variable yield— often referred to as "dial-a-yield" — which could be set between 5 and 80 kilotons.
The Pershing Ia missile was armed with a 400 kiloton W50 warhead. By the early 1970s it was clear that this was far too large to allow the missile to be used as a tactical nuclear weapon — by this time 400 kt was larger than most strategic warheads. The Pershing II had a high accuracy maneuverable reentry vehicle (MARV), equipped with a radar terminal guidance system and carrying a low yield W85 warhead. Like many US nuclear weapons, it was a development of the B61 nuclear bomb - in this case, a modification of the Mod 3/4 design.
After the Pershing missiles were scrapped, all 120 of the W85 warheads produced were modified into B61 bombs, in this case the B61-10 free-fall weapon.
The W85 was a cylinder 13 inches (33 cm) in diameter and 42 inches (110 cm) long. The warhead weighed 880 pounds (400 kg). It had a variable yield from 5 to 80 kilotonnes of TNT (21 to 335 TJ).
Assuming a detonation on the surface at the maximum 50 kt yield, W85 would result in a fireball 160 metres (525 feet) across lasting just over one second. The radiated heat would be sufficient to cause lethal burns to any unprotected person within 3.4 kilometres (2.1 mi). Blast effects would be sufficient to collapse most residential and industrial structures within a 2.7-kilometre (1.7 mi) radius; within 1-kilometre (0.62 mi) virtually all above-ground structures would be destroyed and blast effects would inflict near 100% fatalities. Within 1.8 kilometres (1.1 mi) a 500 rem dose of ionising radiation would be received by the average person, sufficient to cause a 50% to 90% casualty rate - though it is unlikely that anyone would live to suffer the ill effects of this radiation given the thermal and blast effects at this distance.
Significant amounts of nuclear fallout would be created and dispersed into the atmosphere.
It is worth noting that even this small tactical warhead was considerably more powerful than the weapons used in the atomic bombings of Hiroshima and Nagasaki combined.
- W25 - small yield warhead used in AIR-2 Genie air-to-air missile
- W54 - very small yield warhead, one of the smallest warheads built
- B61 - basis for most US weapons today
- B61 Family - overview of bombs derived from the B61 bomb.
- W80 - warhead which armed nuclear cruise missiles
- W81 - development of the W61 for the Navy's Standard missile
- W84 - similar development for the Air Force's aborted GLCM missile
- W88 - warhead in the Trident missile
- http://www.nuclearweaponarchive.org/Usa/Weapons/Allbombs.html, accessed Oct 2, 2006
- http://www.nuclearweaponarchive.org/Usa/Weapons/B61.html, accessed Oct 2, 2006
- http://www.globalsecurity.org/wmd/systems/b61.htm, accessed Oct 2, 2006
- The B61 family of bombs, Robert Norris The Bulletin of the Atomic Scientists
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