The Department of Energy said Friday it has started building the first low-yield, submarine-launched ballistic missile warhead ordered by the Donald Trump administration last year.

“The Pantex Plant has initiated assembly of the W76-2 First Production Unit,” a spokesperson for the agency’s semi-autonomous National Nuclear Security Administration (NNSA) wrote in response to a Defense Daily query. “NNSA is on track to complete the W76-2 Initial Operational Capability warhead quantity and deliver the units to the Navy by the end of Fiscal Year 2019.”

The W76-2 will be a modified version of the far more powerful W76-1 warhead. The NNSA in December finished a decades-long W76-1 modernization program that cost an estimated $4 billion. The semiautonomous Department of Energy agency says the modernization will keep W76-1 war-ready for another 30 years.

An artist’s rendering of the U.S. Navy’s future Columbia-class submarine, which will carry the W76-2 ballistic missile warhead (Image: U.S. Navy )

The Trump administration ordered W76-2 in its 2018 Nuclear Posture Review, insisting the U.S. needs a low-yield weapon to stop Russia from using similarly powerful nuclear weapons to win a war Moscow starts, but cannot finish, with conventional weapons. The NNSA has said it will convert “a small number” of W76-1 warheads into W76-2 warheads.

Congressional Democrats strongly oppose the W76-2, which they say will precipitate an arms race and increases the chances of a conventional conflict escalating into all-out, civilization-ending nuclear war. New House Armed Services Committee Chairman Adam Smith (D-Wash.) has said he will introduce legislative language to ban the W76-2. Smith’s office did not immediately reply to a request for comment.

Last year, the GOP-controlled Congress approved $65 million for the W76-2 in 2019. Sen. Dianne Feinstein (D-Calif.), who strongly opposes the weapon, said in April the NNSA needs some $60 million more for the effort in 2020, raising the total cost of W76-2 to a minimum of $125 million.

The NNSA spokesperson did not say exactly when work on the first W76-2 production unit started. However, the agency finished the W76-1 life extension program in December, which cleared up people and equipment to start work on W76-2.