The W85 was a thermonuclear warhead developed by the United States of America to arm the Pershing II missile. It had a variable yield

Variable yield

Variable yield — or dial-a-yield — is an option available on most modern nuclear weapons. It allows the operator to specify a weapon's yield, or explosive power, allowing a single design to be used in different situations...

— often referred to as "dial-a-yield" — which could be set between 5 and 80 kilotons.

Overview

The Pershing Ia missile was armed with a 400 kiloton W50

W50 (atomic weapon)

The W-50 or W50 thermonuclear warhead was a nuclear bomb used on the MGM-31 Pershing intermediate range nuclear missile.There were two major variants produced , in three yield options .All variants were in diameter and long, weighing .The W50 used the Tsetse primary design...

 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

Tactical nuclear weapon

A tactical nuclear weapon refers to a nuclear weapon which is designed to be used on a battlefield in military situations. This is as opposed to strategic nuclear weapons which are designed to menace large populations, to damage the enemy's ability to wage war, or for general deterrence...

 — by this time 400 kt was larger than most strategic warheads. The Pershing II had a high accuracy maneuverable reentry vehicle

Maneuverable reentry vehicle

The maneuverable reentry vehicle is a type of ballistic missile warhead capable of shifting targets in flight...

 (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

B61 nuclear bomb

The B61 nuclear bomb is the primary thermonuclear weapon in the U.S. Enduring Stockpile following the end of the Cold War. It is an intermediate yield strategic and tactical nuclear weapon featuring a two-stage radiation implosion design....

 - 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.

Specifications

The W85 was a cylinder 13 inches in diameter and 42 inches long. The warhead weighed 880 pounds. It had a variable yield from 5 to 80 kilotons

TNT equivalent

TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...

.

Effects

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 kilometres (1.7 mi) radius; within 1 kilometre (0.621372736649807 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

Nuclear fallout

Fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and shock wave have passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes...

 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

Atomic bombings of Hiroshima and Nagasaki

During the final stages of World War II in 1945, the United States conducted two atomic bombings against the cities of Hiroshima and Nagasaki in Japan, the first on August 6, 1945, and the second on August 9, 1945. These two events are the only use of nuclear weapons in war to date.For six months...

 combined.

See also

• W25 - small yield warhead used in AIR-2 Genie air-to-air missile
  Air-to-air missile
  An air-to-air missile is a missile fired from an aircraft for the purpose of destroying another aircraft. AAMs are typically powered by one or more rocket motors, usually solid fuelled but sometimes liquid fuelled...
  
  
• W54
  W54
  The W54 was the smallest nuclear warhead deployed by the United States. It was a very compact implosion-type nuclear weapon design, designed for tactical use and had a very low yield for a nuclear weapon.- Development :...
  
   - very small yield warhead, one of the smallest warheads built
• B61
  B61 nuclear bomb
  The B61 nuclear bomb is the primary thermonuclear weapon in the U.S. Enduring Stockpile following the end of the Cold War. It is an intermediate yield strategic and tactical nuclear weapon featuring a two-stage radiation implosion design....
  
   - basis for most US weapons today
  • B61 Family
    B61 Family
    The B61 Family is a series of thermonuclear bombs and thermonuclear warheads based on the B61 nuclear bomb.-Initial development:The B61 bomb was developed by Los Alamos Scientific Laboratory starting in 1960...
    
     - overview of bombs derived from the B61 bomb.
• W80 - warhead which armed nuclear cruise missiles
• W81
  W81
  The W81 thermonuclear warhead was a planned US warhead to be mounted on the SM-2 surface to air missile used by the US Navy. The W81 was a design derivative of the B61 nuclear bomb as many other modern US warhead designs are...
  
   - development of the W61 for the Navy's Standard missile
  Standard missile
  Standard Missile can refer to a family of several different American missiles:* RIM-66 Standard , a medium range surface-to-air missile, the successor of the RIM-24 Tartar missile...
  
  
• W84
  W84
  The W84 is an American thermonuclear warhead designed for use on the BGM-109G Gryphon Ground Launched Cruise Missile . It is a derivative of the B61 nuclear bomb design and a close relative of the W80 warhead used on the AGM-86 ALCM, AGM-129 ACM, and BGM-109 Tomahawk SLCM cruise missiles.The W84...
  
   - similar development for the Air Force's aborted GLCM missile
• W88
  W88
  The W88 is a United States thermonuclear warhead, with an estimated yield of 475 kiloton , and is small enough to fit on MIRVed missiles. The W88 was designed at the Los Alamos National Laboratory in the 1970s. In 1999 the director of Los Alamos who had presided over its design described it as...
  
   - warhead in the Trident missile
  Trident missile
  The Trident missile is a submarine-launched ballistic missile equipped with multiple independently-targetable reentry vehicles . The Fleet Ballistic Missile is armed with nuclear warheads and is launched from nuclear-powered ballistic missile submarines . Trident missiles are carried by fourteen...