Sentinel: US Air Force considers buying land for up to 120 new ICBM silos to replace Minuteman III

The US Air Force is considering buying land to build up to 120 new silos for the LGM-35A Sentinel intercontinental ballistic missile, which will replace the ageing Minuteman III. The plan is contained in a Notice of Intent published by the Department of the Air Force in the Federal Register on October 9, for a Supplemental Environmental Impact Statement (SEIS).

The figure of 120 comes from an analysis by Air & Space Forces Magazine, based on data from the study’s official website.

Where the new silos could go

According to the proposed action page, the Air Force is considering acquiring land for new silos at three bases, west and east of the existing missile fields:

• up to 30 new silos at F.E. Warren Air Force Base, Wyoming
• up to 30 at Malmstrom Air Force Base, Montana
• up to 60 at Minot Air Force Base, North Dakota

At Malmstrom the Air Force is also examining reusing the former sites of the 564th Missile Squadron for up to 60 new silos. Each silo is planned to take up to 12 acres (about 48.5 decares) and each launch centre up to 16 acres (about 65 decares). Each missile field will keep 150 silos operational throughout the transition.

Why the plan changed

The original study, in March 2023, envisaged converting the existing Minuteman launch facilities into Sentinel silos. According to the notice, this “could not proceed, because key milestones of the Sentinel programme were no longer achievable due to cost and schedule risks” of the conversion. After the programme was restructured in July 2024, the Air Force turned to “modern, newly built silos, adaptable to future technological developments”. The no-action alternative, keeping the 2023 plan, was judged “infeasible”.

The programme suffered a Nunn-McCurdy cost breach in early 2024, before the Pentagon certified its continuation. The 450 active Minuteman silos will be replaced one for one. The old silos will be closed by backfilling, demolition, burial or controlled implosion, while selected launch centres will be able to refuel and arm the new MH-139 Grey Wolf helicopters.

Timeline

The public scoping period runs for 30 days from October 9. The draft study is expected for comment in autumn 2027 and the final study in spring 2028. After that, the Secretary of the Air Force will be able to sign the decision allowing land purchase and construction.

The study website says the Sentinel is moving toward flight tests in 2027. The modernisation of the land-based leg is part of Washington’s wider effort on the nuclear triad, for which the 2027 budget request provides $71.4 billion. The Minuteman III, which is to be replaced, is still tested regularly.