Late delivery of high explosives to the Lawrence Livermore National Laboratory will delay by “at 2 two months” the National Nuclear Security Administration’s W80-4 program to refurbish an old warhead for a next-generation air-launched cruise missile, the Government Accountability Office reported Monday.

Livermore, which leads the W80-4 life-extension program, needs the high explosives for a hydrodynamic test intended to prove out computer simulations about how the refurbished warhead would behave during detonation, the Government Accountability Office (GAO) wrote.

The Holsten Army Ammunition plant in Tennessee was supposed to fill Livermore’s order in March 2019, but did not, according to GAO. First, the BAE Systems-operated plant delayed the delivery to fill a Department of Defense order deemed higher priority than Livermore’s.

Then, there was a fire at Holsten in January that halted production for about three weeks, GAO wrote. The tidbit was tucked into a report about the National Nuclear Security Administration’s (NNSA) projected need for conventional high explosives to refurbish the existing U.S. nuclear arsenal. Conventional explosions spark nuclear detonations.

NNSA is refurbishing the W80 for the Long Range Standoff Weapon: the Pentagon’s planned replacement for the 1980s-vintage Air Launched Cruise Missile. The Defense Department wants to deploy the new missile in 2025. Initially, B-52H aircraft would carry the weapon. Eventually, the planned B-21 Raider would carry it.

The cost of W80-4 has risen somewhat even since last year. In March, NNSA requested almost $900 million for the program for fiscal year 2020. In 2018, the agency estimated it would need around $715 million for W80-4 for the fiscal year that begins Oct. 1.

NNSA has not said, specifically, what caused the cost increase.

The House Armed Services and Appropriations Committees have each approved the $900 million requested for W80-4 for 2020, the former in a 2020 National Defense Authorization Act awaiting a floor vote, the later in a 2020 Energy and Water appropriations act being debated this week on the floor.

The Senate Armed Services Committee approved full funding for W80-4 in its own version of the 2020 National Defense Authorization Act. The Senate Appropriations Committee has not drafted a 2020 NNSA spending bill yet.