The Mk4 reentry system, developed jointly in the early 1970's by the Navy Strategic Systems Programs and the Department of Energy (DOE), is specifically designed to house the missile's W76 nuclear warhead.

Additionally, it provides thermal protection for the warhead from the harsh reentry environment while ensuring accurate delivery of the payload to its intended target.

The first W76/Mk4 reentry body entered the nation's nuclear stockpile in 1979, and today comprises the largest percentage of any strategic weapon in the US nuclear inventory.

"The Mk4 reentry body is the mainstay of our nation's nuclear deterrent," said Duke Williams, Space Systems chief systems engineer for Navy Reentry Systems. "It has proven to be one of the safest and most reliable weapons in our nuclear arsenal."

Missiles & Space received the first Mk4 production contract in 1976 and full-rate manufacturing began in 1977. Since that time, Missiles & Space has manufactured more than 5,000 Mk4 reentry body assembly kits for the U.S. and U.K. Navies. Each Trident missile carries multiple W76/Mk4 reentry bodies.

The W76/Mk4 reentry body is assembled at the DOE PANTEX facility from hardware supplied by Missiles & Space, including the reentry body aeroshell, RF subsystem, nose-tip and complete release assembly.

Current Department of Defense plans call for the W76/Mk4 reentry body to support FBM operations until 2040. To meet this service life requirement, the Navy and DOE are planning a life extension program for the W76/Mk4.

This program, slated to start early this decade, is projected to be complete around 2020. To support this effort, Missiles & Space will retain all Mk4 production tooling and most manufacturing capabilities.