The W76/Mk4 reentry body assembly (RBA) on Trident I (C4) and Trident II (D5) strategic weapon systems are a key component of the Nation's strategic deterrent force designed and produced between 1972 and 1987. Meeting this mission will require that the W76/Mk4 RBA be deployed well beyond its original service life of 20 years.

Aging concerns, the non-availability of replacement components used in original designs, and a desire to modernize nuclear safety features requires a refurbishment of the W76/Mk4 RBA for it to meet the extended service life. This should be accomplished in a planned, methodological manner to prevent possible weapon downtime and the total consumption of the National Nuclear Security Agency (NNSA) nuclear weapons complex capacity that could occur if a critical problem were identified. The US Navy Strategic Systems Programs (SSP) requested and the Nuclear Weapons Council Standing and Safety Committee (NWCSSC) approved a joint Department of Defense (DOD)/DOE Phase 6.2/6.2A Study, which was initiated on 19 October 1998. The study was conducted under the W76/Mk4 Project Officers Group (POG). The results of the study were briefed by the W76/Mk4 POG to the NWCSSC on 8 December 1999 and to the Nuclear Weapons Council (NWC) on 13 March 2000.

Study ground rules included the following:

• Modernize nuclear detonation safety features (to Mk5-like interface)
• Consider W76/Mk4 on Trident II (D5) only
• Current W76/Mk4 Military Characteristics (MCs) and Stockpile-To-Sequence (STS) were baseline
• Plan for a one-time refurbishment process (DOD and NNSA)
• Plan for total stockpile quantities reflected in the current Long Range Planning Assessment (LRPA)
• Production duration goal of 10 years or less
• Goal for a post-refurbishment life extension of 30 years

Emphasis was placed on meeting performance requirements over the extended life and minimizing the cost of necessary refurbishment.

The drivers for refurbishment are fourfold:

1. The W76/Mk4 is the most critical element of our nation's strategic deterrent and cannot be allowed to be degraded by a serious aging problem;
2. The W76/Mk4 Dual Revalidation Program has shown that even though components are aging gracefully, there are some negative changes;
3. The Stockpile Surveillance Program cannot predict failures; rather, it only detects them when they appear and when it may be too late to prevent degradation; and
4. The Navy has expressed the desire to retain an average system age of no more than 30 years, compatible with life extension of the Trident Weapon system.