The National Nuclear Security Administration (NNSA) late last year finished refurbishing the final submarine-launched W76 ballistic missile warheads for another 30 years of service, the agency confirmed.

The NNSA finished building the last W76-1 warhead in December, an agency spokesperson said Tuesday by email. The semiautonomous Department of Energy agency started planning for the W76-1 life-extension program in 1999 and delivered the first war-ready warhead to the Navy in 2008. The whole project cost about $4 billion, according to the NNSA’s 2019 Stockpile Stewardship and Management Plan.

The Washington-based Federation of American Scientists estimated the NNSA planned to modernize some 1,500 W76 warheads.

With the W76-1 ready for deployment on Trident II-D5 missiles carried by Ohio-class submarines, the NNSA’s W76 production line is now clear to start work on the proposed W76-2 warhead: a low-yield version of the weapon ordered by the Donald Trump administration last year in the 2018 Nuclear Posture Review.

Rep. Adam Smith (D-Wash.), chairman of the House Armed Services Committee for the 116th Congress, has said he wants to cancel the W76-2.

For fiscal 2019, last year’s fully GOP-led Congress appropriated $65 million for W76-2. The Trump administration says it needs such a weapon to stop Russia from using similarly powerful nuclear weapons to win a war Moscow begins, but cannot finish, with conventional weapons. Proponents claim existing low-yield options, such as the B61 gravity bomb carried by aircraft, cannot quickly strike targets deep inside Russian territory.

It was not clear at deadline for Defense Daily whether the NNSA had started any production work on W76-2. The agency estimates W76-2 will cost at least $125 million to build, Sen. Dianne Feinstein (D-Calif.) said in appropriations markups in 2018. The NNSA estimates it will take until 2023 to finish making the weapon, according to the agency’s 2019 stockpile Stewardship and Management Plan.