US begins final assembly of B61-13 nuclear gravity bombs

The United States has entered the final stage of assembling the B61-13, a modernised high-yield nuclear gravity bomb, at the Pantex Plant in Texas, according to data from the U.S. National Nuclear Security Administration (NNSA).

Earlier in September, NNSA announced that the Y-12 National Security Complex near Oak Ridge, Tennessee, had completed production of the final batch of canned subassemblies required for the B61-13 program. The production and formal acceptance testing of those components were completed about seven months ahead of schedule.

The components will now be assembled into complete B61-13 bombs at the Pantex Plant before the finished weapons are transferred to the U.S. military stockpile.

The B61-13 modernisation program was launched in 2023. NNSA completed the first B61-13 unit at Pantex in May 2025, nearly a year ahead of its original target date. The bomb is designed for delivery by U.S. strategic bombers, including the B-2 Spirit and the future B-21 Raider.

The B61-13 uses the warhead from the older B61-7 while incorporating modern safety, security and accuracy features derived from the B61-12. Its maximum yield is 360 kilotons, significantly higher than the B61-12’s maximum yield of 50 kilotons.

U.S. officials have said the B61-13 program will not increase the overall number of nuclear gravity bombs in the U.S. arsenal, as the new weapons are intended to replace older variants rather than add to the stockpile.

Experts at the Federation of American Scientists have assessed that the number of B61-13 bombs produced is likely to be limited, potentially to around 50 units, because the number of targets requiring a high-yield nuclear gravity bomb is considered relatively small.

By Tamilla Hasanova