The Air Force broke ground Feb. 13 on a prototype silo for the Northrop Grumman LGM-35A Sentinel future intercontinental ballistic missile at the company’s Promontory, Utah, site, officials said at the Air & Space Forces Association’s warfare symposium.
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 Sentinel missile will replace the Boeing Minuteman III intercontinental ballistic missile. The National Nuclear Security Administration’s plutonium pit production program at Los Alamos National Laboratory plans to make the fissile cores for the W87-1 warhead, which will top the Sentinel missile.
In the last year, the service decided to build new silos for Sentinel, rather than re-using those housing Minuteman IIIs. Environmental factors in the Minuteman III silos include asbestos, lead paint, and tilting in a small number of silos due to their variations in their concrete thickness.
“The pivot to the new silos was not driven by the size of the [Sentinel] missile,” a Sentinel program official told reporters, including Exchange Monitor affiliate publication Defense Daily, last week at the symposium. “It is a little bit larger, 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 plans to build modular Sentinel silos that would use pre-cast concrete and standardized components to reduce construction cost and time, but the approach may also mean less silo hardening and present logistical challenges in transporting the large modules, which would be dropped into place at existing 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.
The Sentinel program official said that variability in the Minuteman III silos and a desire to reduce cost were key in the Air Force’s decision to build new ones.
“The first thing we looked at is just the variability of refurbishing Minuteman III silos for Sentinel,” the official said. “Just like trying to renovate a house built in the 1960s, there was variability in understanding how you would attack refurbishment, how you would understand the conditions and the timing of that, and the cost associated with that. The second factor we looked at was, as we were looking at opportunity space we found a squadron at Malmstrom which was the first one that was still owned Air Force land.”
The official added, “that allowed us what I would call ‘swing space’–if we constructed there, how we sequence and choreograph, taking down Minuteman and bringing Sentinel up on alert. It allowed us the opportunity to do that without impacting operations today, and going after that ‘swing space’ drove us to designing and constructing new silos, as there were not Minuteman III silos available to be reused on those sites.”
Another issue for Sentinel has been software development.
“Sentinel is software-intensive, and development progress remains slower than anticipated,” according to a Government Accountability Office (GAO) two-page ‘national security snapshot‘ last week on Sentinel. “These delays have raised concerns from program officials about the prime contractor’s ability to complete the program’s software in a timely manner. Software risks remain because, notwithstanding how long the program has been in development, the Air Force and Sentinel contractor have yet to finalize software design or software development metrics, and are re-planning the delivery schedule.”
The snapshot “dates back to 2025 and does not reflect where we are today, working with Northrop Grumman and highlighting my expectations as we replace the software,” Air Force Lt. Gen. Dale White, the Air Force’s critical major weapon systems, including Sentinel, told reporters. “Northrop Grumman has some great experience in this area from their time on B-21 and other programs.”
“Most importantly, it’s open enough that we can evolve the software so that we can improve the capability, as the threat evolves,” White added.
Exchange Monitor affiliate Defense Daily first published a version of this article.