The W87 is an American thermonuclear missile warhead. It was created for use on the MX or Peacekeeper ICBM, 50 of which, with up to 12 warheads per missile, were deployed 1986–2005. Starting in 2007, 200 of the W87 warheads from now-retired MX/Peacekeeper missiles will be retrofitted onto much older Minuteman III missiles, with only one warhead on each missile.
Design of the W87 started in February 1982 at Lawrence Livermore National Laboratory and production of the warhead began in July 1986 and ended in December 1988. Its design is reportedly somewhat similar to the W88, though that warhead was designed at Los Alamos National Laboratory. The weapons were refurbished for a lifespan by the National Nuclear Security Administration's Life Extension Program.
The W87 design includes all modern safety features, including insensitive high explosives LX-17 and PBX-9502 (primary component TATB), a fire resistant pit, and advanced arming and fuzing safety features.
The original yield of the W87 was 300 kilotons of TNT, but has the announced ability to be upgraded to a yield of 475 kilotons, presumably by using more HEU in the fusion secondary stage tamper. It is not known if that upgrade was completely tested or merely designed and ready to implement.
The exact dimensions of the W87 are classified, but it fits inside the Mk. 21 reentry vehicle, which is a cone with base diameter of 22 inches (55 cm) and a length of 69 inches (175 cm). The weight is believed to be between 440 and 600 pounds (200 and 270 kilograms).
In addition to the higher yield upgrade option described above, a specific variant W87-1 entered Phase 3 development engineering and was assigned its type designation in November 1988. This variant was intended for the MGM-134 Midgetman small ICBM missile and was intended to have the full 475 kiloton yield. The Midgetman and W87-1 were cancelled in January 1992.