WASHINGTON ― The United States’ B61-12 nuclear gravity bomb may face an 18 month delay during production, with the W88 submarine-launched ballistic missile warhead facing a shorter delay, a top National Nuclear Security Administration official confirmed Wednesday.

The B61-12 life-extension program consolidates and replaces the older B61-3, -4, -7 and -10 variants, while the W88 Alteration 370 is meant to replace the arming, fuzing and firing subsystem for the W88 warhead for the Trident II sub-launched ballistic missile. The two are among five major modernization programs underway at the agency.

Both had been due for production in 2020, but neither will have their first production units delivered on time, according to Charles Verdon, the National Nuclear Security Administration’s deputy administrator for defense programs. NNSA is working with the Defense Department to minimize the delays, but Congress has been informed both will be ready “roughly around the same time,” Verdon said at the at the 2019 Defense News Conference.

The issue stems from off-the-shelf parts used in both weapons. Both systems are planned to work for 20-30 years, and heavy stress testing of the parts raised questions for NNSA officials about whether the parts would survive for three decades. Rather than risk the pieces failing years in the future, officials decided to seek replacements now and delay moving forward with the program.

However, Verdon said the 18-month delay for the B61-12 might shrink in the future, as the agency gains more insight on parts procurement and integration.

Kingston Reif, director for disarmament and threat reduction policy at the Arms Control Association, warned that the first production unit’s target date is likely to increase the estimated $7.6 billion cost of the program. The delay could also hinder NNSA’s ability to execute several other planned life-extension programs on time and on budget, he added.

While NNSA’s Office of Cost Estimating and Program Evaluation in 2017 projected a total program cost of approximately $10 billion and a two-year delay to the agency’s first production-unit date, the agency maintained that the B61-12 life-extension program was on time and on budget.

“The delay to both the B6-12 and W88 ALT 370 highlights the enormous scope of work already on NNSA’s overburdened plate and the significant execution challenges facing the modernization effort," Reif said.

The fate of another modernization program, a low-yield variant submarine weapon known as the W76-2, is expected to be determined as the House and Senate resolve their separate versions of the National Defense Authorization Act. Among a range of differences on nuclear issues, the Democratic-led House bars funding for the deployment of the W76-2, cutting the entire $19.6 million Defense Department request and $10 million Energy Department request for the program.

On Wednesday, Robert Soofer, the deputy assistant secretary of defense for nuclear and missile defense policy, pointed to support for the W76-2 from both current leaders and former Obama administration officials, predicting “trades” between the House and Senate bills.

Updated 9/5/19 to clarify the impact of the delay.