NNSA has completed the Last Production Unit of the W88 Alteration 370, a multiyear program to modernize the W88 nuclear warhead carried onboard Ohio-class ballistic missile submarines.
National Nuclear Security Administration
December 16, 2025
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WASHINGTON – The Department of Energy’s National Nuclear Security Administration (NNSA) has completed the Last Production Unit (LPU) of the W88 Alteration (Alt) 370, a multiyear program to modernize the W88 nuclear warhead carried onboard Ohio-class ballistic missile submarines. The W88 first entered the U.S. nuclear stockpile in 1988, and the process to upgrade the warhead reached full production in 2022. The W88 Alt 370 program addressed aging issues identified during routine surveillance, enhancing the reliability of a critical element of the sea-based leg of America’s strategic deterrent. This milestone marks the concluding phase of one of seven ongoing major warhead modernization programs.
“Completing the W88 Alt 370 is the latest instance of NNSA delivering modernized nuclear weapons to the Department of War at the pace and scale needed to fulfill our deterrence requirements,” said NNSA Administrator Brandon Williams. “Achieving two LPUs for the B61-12 and W88 and the FPU for the B61-13 all within a single year demonstrates our ability to execute NNSA's fundamental production mission. This record of delivery signals to our adversaries and our allies and partners alike that under President Trump’s leadership, the United States has the will and the means to field newer, safer, and more capable warheads for our strategic deterrent."
This W88 Alt 370 program included replacing the warhead’s arming, fuzing, and firing assembly, adding a lightning arrestor connector, refreshing the conventional high explosives within the weapon, and concurrently replacing limited-life components.
NNSA, in coordination with the U.S. Navy, delivered the last upgraded W88 Alt 370 warhead four years after achieving the First Production Unit (FPU) in July 2021. NNSA’s program managers and experts from Los Alamos National Laboratory, Sandia National Laboratories, the Pantex Plant, the Y-12 National Security Complex, and the Kansas City National Security Campus collaborated on the design, development, qualification, and component production.
“Completion of the last W88 Alt 370 testifies to the successful collaboration we’ve had with our U.S. Navy and Department of War partners,” said David Hoagland, NNSA Acting Deputy Administrator for Defense Programs “The momentum built through the production and delivery of the W88 Alt 370 will continue into our expanding weapons modernization programs and additional stockpile efforts in the coming years.”
Following completion of the last W88 unit, Pantex will continue production of W88 Alt 370 warheads and components to support future surveillance of the warhead. NNSA continues modernizing warheads for all three legs of the nuclear triad to maintain high reliability and to add additional capabilities at the pace required to meet evolving deterrence challenges. For the sea-based leg, these efforts include ongoing programs to deliver the W93 and SLCM-N warheads, with FPUs for both weapons expected in the early to mid-2030s.
As the W88 Alt 370 program completes its final production activities and transitions to sustainment, the program’s same staff are already pivoting to focus more fully on accelerating the SLCM-N program. NNSA continues to execute six additional warhead modernization programs while also modernizing the full suite of production manufacturing capabilities necessary to meet evolving nuclear deterrence requirements.