Sometime between October and December, the National Nuclear Security Administration’s programs to refurbish its B61 bombs and W88 warheads reached the halfway mark, an agency spokesperson said Monday.

Production of the B61-12 Life Extension Program and W88 Alt 370 reached the halfway mark, with at least 50% of the required weapons produced and delivered to the two services, an NNSA spokesperson wrote in an email to the Exchange Monitor.

“The B61-12 Life Extension Program and W88 Alteration 370 programs reached the 50% production milestone in Q1 of FY 2024,” the spokesperson said. “The last production units for the B61-12 and W88 Alt 370 are each scheduled for FY 2025.”

NNSA would not say how many of each warhead was scheduled for production nor how many have been produced because production numbers are only released in conjunction with the Department of Defense. The agency announced the milestone in early December but did not publicly elaborate until this week.

That the mass production phases of both programs, carried out by Led by Consolidated Nuclear Security (CNS) at the Pantex Site in Texas, hit the milestone around the same time was a unique achievement, the NNSA said.

It was also not planned, said the NNSA spokesperson.

“Production timelines are set to meet DoD operational requirements, so achieving the production milestone around the same time for each program was coincidental and not a factor in determining production schedules,” the NNSA spokesperson said. 

The B61-12 is a gravity bomb and the oldest in the U.S. arsenal. The W88 nuclear warhead entered the stockpile in late 1988 and is deployed on the U.S. Navy’s Trident II D5 Submarine-Launched Ballistic Missile system.

The U.S. Air Force deploys the B61 gravity bomb on multiple platforms and has been in service more than 50 years, making it the oldest weapon in the U.S. stockpile, said Carlos Alvarado, deputy field office manager for the NNSA Production Office, in the Dec. 5 statement. The W88 first entered the stockpile in the late 1980s. The W88 Alt 370 includes numerous updates to address aging concerns and enhance nuclear safety, he said.

NNSA delivered the B61-12 first production unit in November 2021, and received authorization to enter Phase 6.6, or full-scale production, in June 2022. The estimated coast for completion of the program was $9.5 billion in the NNSA’s most recent Stockpile Stewardship and Management Plan, published in November. The W88 Alt 370 program was estimated to cost about $3.3 billion, according to the plan.