US Air Force artist’s rendering of the Sentinel in flight. (Credit: US Air Force)

WASHINGTON — A first flight of the Air Force’s intended replacement for its nuclear-armed Minuteman III ballistic missile fleet has slipped by over two years, the Air Force confirmed today to Breaking Defenselikely adding scrutiny to one of the Pentagon’s most expensive projects that also recently suffered a “critical” cost breach.

Previous budget documents showed that the LGM-35A Sentinel ICBM program planned to carry out its first flight test in December 2023. As recently as February 2023 an Air Force official said the flight test remained “on track.” But that test has not yet taken place, and the fiscal year 2025 documents now indicate that the missile isn’t planned to fly until February 2026.

In a statement to Breaking Defense today, an Air Force spokesperson confirmed the significant schedule slip, saying that “Sentinel’s first flight test was delayed due to increased lead times for guidance computer components.”

“While first flight will occur later than initially planned, it is not on the critical path,” they added. “The Air Force and OSD [Office of the Secretary of Defense] continue to work closely together to identify and implement options to reduce risk and optimize schedule.”

As the spokesperson’s comments reflect, the Sentinel’s current schedule is somewhat in flux as Air Force officials reassess the program in the wake of a Nunn-McCurdy cost breach disclosed in January. That breach mandated that the Air Force and OSD identify the root causes of a program price jump of 37 percent to a new total of over $130 billion and to probe a potential two-year delay to the missile’s planned initial operational capability, previously pegged for 2029. That review is expected to conclude this summer.

Today the Air Force spokesperson said that “[e]arly estimates indicate that a large portion of the Sentinel program’s cost growth is in the Command and Launch segment, which is the most complex segment of the Sentinel program.” Officials have said the missile itself is not a primary cause of the cost growth. 

The spokesperson’s comments came after the primary contractor on Sentinel, Northrop Grumman, provided a briefing to reporters earlier this week to defend the program. 

A company official, who spoke on the condition of anonymity, said the government, rather than Northrop, established what turned out to be imprecise initial estimated costs during an earlier stage when the program was still competitive, and the company so far has only bid on the EMD phase. Northrop was awarded the $13.3 billion EMD contract in September 2020 after the cost estimate was completed, the official said.

Since then, new costly factors have arisen, the official said. For example, missile silo designs “have changed since the original concepts that were discussed” during early stages of the program “and even at the beginning of the EMD phase.”

The official also said that the program originally expected that Sentinel could “reuse almost all of the existing cabling” wired to the Minuteman III fleet. New, fiber optic cabling will now be required to support the program, which the Northrop official said “represents a whole lot of new work that wasn’t originally part of the plan” — an issue further complicated by factors like the thousands of miles of cabling that will be required, which in turn can only be laid in by negotiating easements with private landowners. 

The Northrop official indicated more unwelcome discoveries could lay ahead as work continues, which is not stopping despite the ongoing cost breach review.

Through the program, the Air Force is currently planning on refurbishing 450 Minuteman III silos to house Sentinel missiles in their place, but only a “handful” of lidar scans have been conducted to date to assess their condition. Additionally, there hasn’t been much “destructive testing” to assess factors related to the silos’ concrete walls.

Northrop built its own mock Minuteman III silo using internal dollars to help mitigate potential risk, but the step may not be representative of every one of the hundreds of silos scattered across the Great Plains.

And though the company was given access to data from decommissioned silos, Northrop will not get data for live silos slated for refurbishment until around when the work is supposed to start, the company official said. The limited ability to do evaluations means there is “certainly the potential that when they get to investigating more of the silos, they may find that some of them might not be possible [to use],” the official said.

Northrop’s “main construction partner” is Bechtel, the official said, adding that Clark Construction is serving an advisory role.

Proponents of the Sentinel program say that the newly-revised costs are justified, whereas opponents point to the price spike as a reason to explore alternatives. Highlighting the estimated cost of the Navy’s Columbia submarine program, whose pricetag for 12 subs would be roughly equal to the revised cost of the Sentinel program, the Northrop official argued that Sentinel is a “relatively affordable” piece of the nuclear triad. 

The Northrop official emphasized the enormous complexity of the Sentinel endeavor, repeating sentiments from Air Force leaders that the program is essentially composed of multiple major acquisition efforts – such as the missiles, silos, launch centers and other components — rolled into one. And as officials search for accountability in the large cost increase to be borne by taxpayers, the Northrop official was reluctant to lay blame.

“Looking for that blame, I think, is hard because it really was just an immense challenge,” they said. 

It’s unclear if such a sentiment would satisfy some lawmakers, like Sen. Elizabeth Warren, who grilled US Strategic Command chief Gen. Anthony Cotton earlier this month over Sentinel’s troubles.

“… [W]e have to have a plan here that is actually going to work,” Warren, a Massachusetts Democrat, said on March 4. “We can’t just keep burning money and say, ‘At some point we hope we will be able to deliver this thing.’”