After a year of mounting uncertainty in the effort to upgrade the land-based leg of the U.S. nuclear triad, the Air Force did not test fire the new Northrop Grumman-built LGM-35 Sentinel intercontinental ballistic missile in 2023.

Reached this week by the Exchange Monitor, spokespersons for the Air Force and Northrop Grumman declined to answer questions about the launch that had been scheduled for Dec. 23. In its 2024 budget request, released in March, the Air Force held to the December launch date.

Sentinel is scheduled to achieve initial operational capability in May 2029 to begin replacing the 400 Boeing-built Minuteman III intercontinental ballistic missiles currently in service, but the new missile is behind schedule. 

The 2024 National Defense Authorization Act, signed Dec. 22, requires the Pentagon to whip up an integrated master schedule for Sentinel and deliver monthly briefings to Congress about the missile. That follows a Defense Department report, sent to the Hill in September, which showed a possible 10-month delay in the estimated $95.8 billion development effort.

When first deployed, Sentinel will carry the W87-0 warhead, which will be taken from Minuteman III missiles and adapted for the Northrop-built successor. Later Sentinel missiles will use the W87-1, newly manufactured copies of the Minuteman’s W78, but with freshly cast pits provided by the Los Alamos National Laboratory starting in 2030 or so

With the pit program dealing with its own delays, however, Congress has directed the Air Force to look at a stopgap.

Among other things, the 2024 National Defense Authorization Act calls for the Air Force to study “the feasibility and advisability of initiating immediate deployment of W78 warheads to a single wing of the intercontinental ballistic missile force as a hedge against delay of the LGM-35A Sentinel intercontinental ballistic missile.”

Air Force Secretary Frank Kendall told the House Armed Services Committee in April that it will be a challenge for Sentinel to reach initial operational capability on time.

Brig. Gen. Colin Connor, the Air Force’s director of intercontinental ballistic missile modernization, said in December that the LGM-35 Sentinel, formerly known as the Ground-Based Strategic Deterrent, can carry several of the W87-0 or W87-1 warheads.