# W87

The W87 is an American thermonuclear missile warhead formerly deployed on the LGM-118A Peacekeeper ("MX") ICBM. 50 MX missiles were built, each carrying up to 10 W87 warheads in multiple independently targetable reentry vehicles (MIRV), and were deployed from 1986 to 2005. Starting in 2007, 250 of the W87 warheads from retired Peacekeeper missiles were retrofitted onto much older Minuteman III missiles, with one warhead per missile. An upgraded version is planned for use on the forthcoming LGM-35A Sentinel ICBM.

## Description

Design of the W87 (now called the W87 Mod 0 or W87-0) 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 are part of a National Nuclear Security Administration nuclear weapons lifecycle program.
The W87 design includes all modern safety features, including the 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, but it has the announced ability to be upgraded to a yield of 475 kilotons, presumably by using more highly enriched uranium (HEU) in the fusion secondary stage tamper. It is not known if that upgrade was completely tested and ready to implement, or merely designed.
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 (56 cm) and a length of 69 inches (180 cm). The weight is believed to be between 440 and 600 pounds (200 and 270 kg).
The reentry vehicle Mk21 is stored and transported in an H1473 container.

## W87 mod 1

In addition to the higher yield upgrade option described above, a specific variant W87 mod 1 (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 W87-1 had a planned first production unit date of July 1997, but Midgetman and W87-1 were canceled in January 1992.
In 2019, the W87 mod 1 was selected to replace the W78 warhead deployed on all Minuteman III missiles not currently carrying the W87 mod 0. The new warhead will not be deployed onto Minuteman III, but instead be deployed on Minuteman III's replacement ICBM system LGM-35A Sentinel (formerly Ground Based Strategic Deterrent or GBSD). It is not clear if the new W87 mod 1 program is a continuation of the previous W87 mod 1 program, or if it uses any of the physics package developed in the previous W87 mod 1 program.
Information released by the Department of Energy (DoE) on the program states that it "has a similar primary design to the W87-0", which could be evidence that it is like the previous W87 mod 1 program in that it has a different or modified secondary to produce a higher yield. The DoE states that the weapon is based on previously tested nuclear components, with a primary stage containing insensitive high explosives and advanced safety features, but that the weapon does not provide any new military capabilities.
Phase 6.2 Feasibility Study was halted in 2014 before being restarted in 2019. Phase 6.3 Development Engineering is planned to begin July 2022, with 6.4 Production Engineering planned for mid-2026 and 6.5 Initial Production planned for 2030.
It is planned for the Sentinel missile to deploy in 2028, with W87-0 warheads initially being fitted to the system and W87-1 warheads being fitted from 2030 onward. This affords the Air Force a small amount of flexibility if the W87-1 is delayed.