Testing of Northrop Grumman’s and Bechtel’s prototype missile silo for the Sentinel should demonstrate a modular design the service and industry can repeat for all of the 450 planned, new silos, a Northrop Grumman official said last week.

“Proving out the launch silo concept is critical to creating a repeatable approach that will accelerate deployment of a fully fielded Sentinel system,” Sarah Willoughby, vice president and general manager of Northrop Grumman’s strategic systems, said March 26 in a company statement. “The shift in Sentinel silo construction will improve quality and provide a secure, survivable and cost-effective launch silo that is more efficient to maintain.”

On Feb. 13, the Air Force and industry broke ground on the prototype silo at Northrop Grumman’s Promontory, Utah site. The prototype is to allow engineers to test and refine modern construction techniques, validating the new silo design before work begins in the missile fields, the Air Force has said.

“The launch silo modular design concept is a brand-new approach to building and operating the silo,” according to Northrop Grumman. “The new modular approach is survivable, secure, cost effective and easier to maintain than the Minuteman III ICBM system.”

In the last year, the service decided to build new silos for the U.S. Air Force’s LGM-35A Sentinel future intercontinental ballistic missile (ICBM), rather than re-using those housing the Boeing Minuteman IIIs, the current ICBM. Environmental factors in the Minuteman III silos include asbestos, lead paint, and tilting in a small number of silos due to variations in their concrete thickness.

A Sentinel program official said last month that variability in the condition of the Minuteman III silos and a desire to reduce cost were key in the Air Force’s decision to build new ones.

The official said that the Sentinel missile is a “little bit larger” than Minuteman III and “there are some things that come along with that, heavily focused on how we transport it, how it’s emplaced is different that Minuteman III, what vehicles are required to try to make sure that it is transportable on commercial roads and bridges, that we’ve got vehicles that don’t need special handling and things of that nature.”

The Air Force has said that it expects Pentagon acquisition chief Michael Duffey to re-certify Sentinel for engineering and manufacturing development (EMD) this year–months ahead of the Air Force’s earlier estimate of 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 to be May 2029, but slipped to the end of 2033.

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.

In testimony before the Senate Armed Services Committee last week, U.S. Strategic Command head Adm. Richard Correll confirmed Sentinel would achieve Milestone B re-certification by the end of the calendar year.