The Air Force is to start construction this month of a prototype silo for the Sentinel LGM-35A future intercontinental ballistic missile (ICBM) by Northrop Grumman, the service said this week.
The construction is in advance of a planned Pentagon engineering and manufacturing development (EMD) recertification decision on the ballistic missile this year and a first pad-launched flight test next year, the Air Force said in a Tuesday press release.
In February, “teams will break ground on a prototype launch silo at Northrop Grumman’s Promontory, Utah, site,” the service said. “This crucial effort will allow engineers to test and refine modern construction techniques, validating the new silo design before work begins in the missile fields.”
The release also said the restructuring of the Sentinel, which began after the program breached a law known as Nunn-McCurdy in January 2024 by exceeding cost projections by well over the 25% threshold, is expected to be complete by the end of 2026.
The Sentinel silos are to be new rather than refurbished Minuteman silos as the Air Force had planned, in part because of the larger Sentinel missile, but also because of environmental conditions in the silos for the current Minuteman III, including asbestos, lead paint, and tilting in a small number of silos due to variations in their concrete thickness.
The plan to build new silos “avoids the unpredictable costs and safety hazards of excavating and retrofitting 450 unique structures built over 50 years ago, and is a prime example of choosing a path that delivers capability with greater speed and less risk,” the Air Force said.
Last year, the Air Force used a former ICBM silo, Launch Facility 04, at Vandenberg Space Force Base, Calif., and a mock Minuteman III silo built in 2021 by Northrop Grumman in Promontory to inform the service’s decision to build new silos.
Rather than an ICBM test silo, the Air Force is to use a launch pad at Vandenberg for the first flight test of an unarmed LGM-35A, the service said last fall. The Air Force said on Tuesday that it plans to conduct that first flight test next year.
Last year, a Government Accountability Office report said that the Air Force had pushed back the first flight test from 2025 until 2028, but Air Force Deputy Chief of Staff for Strategic Deterrence and Nuclear Integration Lt. Gen. Andrew Gebara said last August that the first Sentinel flight test would be “well prior to” 2028.
The service has considered modular Sentinel silos, which would use pre-cast concrete and standard components to reduce construction cost and time, but that approach could also mean less silo hardening and present logistical challenges in transporting large modules, which would be dropped into place at sites under the 90th Wing at F.E. Warren Air Force Base (AFB), Wyo., the 91st Wing at Minot AFB, N.D., and the 341st Missile Wing at Malmstrom AFB, Mont.
The 90th is to be the first to receive Sentinel, followed by the 341st, and, finally, the 91st.
“This summer, prototyping activities at F.E. Warren AFB will validate innovative utility corridor construction methods, which are key to streamlining the installation of thousands of miles of secure infrastructure and fielding the system faster,” the Air Force said on Feb. 17. “Meanwhile, foundational construction on permanent facilities is already well underway. The first of three new wing command centers is taking shape at F.E. Warren AFB, and critical test facilities are being erected at Vandenberg Space Force Base to support the future flight test campaign.”
If Pentagon acquisition chief Michael Duffey does re-approve Sentinel for EMD this year, that re-certification would be ahead of what the Air Force had planned, namely early to mid-2027.
The Defense Department approved Sentinel to enter EMD in 2020, but then rescinded that decision in 2024 after a critical Nunn-McCurdy unit cost breach.
Initial operational capability for Sentinel was May 2029, but that shifted to the end of 2033.
On Tuesday, the Air Force did not mention 2033 but instead said that it planned “an initial capability targeted for the early 2030s.”
The 659 Sentinel missiles–including 25 for test–are to replace the 450 Boeing Minuteman IIIs–400 deployed and 50 reserve–fielded in the 1970s. The Air Force will likely have a mixed fleet of Sentinel missiles and Minuteman IIIs initially.