The W87 Warhead

Last updated 1 September 2001

Mk-21 RVs mounted on a Peacekeeper (MX) bus. The W87 warhead itself is not visible.
Click for larger image	This image is from the Lawrence Livermore National Laboratory Directorate of Nuclear Weapon website, which was taken after the Wen Ho Lee scandal broke.
Click for larger image
This schematic of the W-87 is from the Cox Committee Report (the Report of the Select Committee on U.S. NationalSecurity and Military/Commercial Concerns with the People's Republic of China). Its accuracy is debatable but the features depicted make sense, and this diagram prompted former weapon physicist Sam Cohen to remark: ... But what should be at least as disturbing is that the Cox report presents a beautiful multicolored diagram (see graphic) that details the workings and components of this highly classified warhead. That is, the Cox report provides an extremely useful blueprint for use by Pakistan or India. Insight Magazine, 16 July 1999

The W87 warhead belongs to the newest missile warhead family, sharing a design similar to the W88. It was designed for use on the Peacekeeper (MX) ICBM. It combines a relatively high yield with increased accuracy to make it an effective hard target kill weapon. It is hardened against nuclear effects, and has enhanced safety features.

Design Features

General

• Two stage radiation implosion weapon;
• U-238 lined radiation case;
• Plastic foam filled radiation channel;
• RV CEP (circle error probability) is <400 feet
• The warhead yield can be upgraded from 300 Kt to 475 Kt by adding rings or a sleeve of oralloy (highly enriched uranium) to the second stage. This probably entails replacing depleted uranium rings used in a cylindrical fusion tamper so that less energetic neutrons can produce additional fission.

• Warhead is more efficient in its use of special nuclear materials than the similar yield W-78. This may refer in part to substituting depleted uranium for U-235 in the secondary.

Primary Stage

• Two-point initiated (two detonator) firing system;
• Uses LX-17 and PBX-9502 insensitive high explosives (IHEs) - a TATB plastic bonded explosive composition. An ultra-fine grain TATB booster is used to fire the main charge.
• Beryllium reflector;
• Fissile plutonium core in the form of a hollow ellipsoidal thin shell;
• Deuterium-tritium gas boosted

Secondary Stage

• Spherical thermonuclear secondary;
• Contains oralloy (highly enriched uranium U-235) as a thermonuclear spark plug;
• U-238 fusion pusher/tamper;
• U-235 as an optional secondary tamper material to boost yield;
• Lithium-6 (95% enrichment) deuteride fusion fuel

Mk-21 RV:

• Alumium substructure, sheathed in graphite-epoxy composite;
• Carbon fiber fabric nose;
• Carbon fiber-phenolic resin heatshield

Delivery Method

Peacekeeper (MX) ICBM (LGM-118A). Each missile carries 10 W-87s, and is based in a hardened underground silo. As the Peacekeeper is retired under the provisions of START-II, these warheads will be used either to rearm Minuteman III missiles as single warhead missiles, or to equip Trident II D5 SLBMs.

Safeguards and Arming Features

• Mechanical arm/safe device (MSAD) used in primary
• Enhanced fire safety through use of:
  • IHE
  • refractory insulation surrounding the primary;
  • fire resistant pit (sealed beryllium refelctor shell capable of withstanding 1000 degrees C for several hours);

See Principles of Nuclear Weapons Security and Safety for explanations of these features.

Fuzing and Delivery Mode

Primary fuze is inertial (i.e. dead reckoning using guidance information)
Secondary dual mode S-band radar fuze (4 antennas) for airburst and surface/proximity fuzing
Fuzing options:

• High altitude airburst
• Medium altitude airburst
• Low altitude airburst
• Surface/proximity burst
• Surface/contact burst

Development

Designed and developed by Lawrence Livermore National Laboratory (LLNL)

Mk-21 RV formerly known as the ABRV (Advanced Ballistic Reentry Vehicle) developed by AVCO Systems Division. Heavier, but higher accuracy and lower cost than the Mk-12A. Tests of the Mk-21's hardness to nuclear effects were conducted in 1984-86:

• Midas Myth/Milagro (Operation Fusileer) 15 May 1984
• Misty Rain (Operation Grenadier) 6 April 1985
• Mighty Oak (Operation Charioteer) 10 April 1986

Design traces its origin to the LASL device tested in the 250 Kt Almendro shot (Operation Toggle), 6 June 1973 (13:00:00.08 UCT). 10 nuclear tests were required to certify the W-87 for stockpiling, including a full yield test prior to March 1976. These tests were complete by mid-1983. The Jefferson shot (Operation Charioteer) 22 April 1986 14:30:00.086 (UCT), 20-150 Kt, may have been a stockpile confidence test of the first production unit, possibly connected with one-point safety concerns.

Development of a higher yield Mod 1 for use on the (now cancelled) single warhead Small ICBM (SICBM or Midgetman) was begun in November 1987, but placed on hold in July 1988. This warhead was to have a higher yield than the Mod 0, which probably indicates the use of the oralloy ring upgrade option for a 475 Kt yield. The U.S. DOE began a life-extension program for W-87 in September 1994. This program is intended to extend the life of the warhead to 2020.

W-87 Development Schedule

February 1982	Development engineering begun at LLNL
October 1983	Production engineering begun
April 1986	First production units completed
July 1986	Quantity production begins
November 1987	Development of W87 Mod 1 begins
July 1988	Development of W87 Mod 1 put on hold
December 1988	Quantity production ends

Deployment

Initial manufacture April 1986
Initial operating capability (10 MX missiles) achieved on 22 December 1986 at Warren AFB
Full deployment December 1988

Originally over 1000 W87s were planned (10 for each of 100 MX missiles). MX deployment was later cut to 50. Some of the warheads are Alt 323 modifications.

Total production: 525 W87-0 warheads

The W-87-0 will remain in the active stockpile under START II, equipping Minuteman III missiles instead of Peacekeepers.