By one estimate, each of the ICBMS and related expenses, such as silo construction, may cost as much as 50% more than the current estimate of $118 million in 2020 dollars not adjusted for inflation. In theory, that could bring the cost for the 659 missiles planned to almost $117 billion.

The Sentinel project, developed and managed by Northrop Grumman Corp., is meant to replace 1970s-era Minuteman III missiles as part of a modernization of all three legs of the air-land-sea triad of nuclear weapons, in part to counter China’s expanding arsenal.

Although that initiative has substantial support in Congress, rising costs could trigger provisions of a 41-year-old law designed to warn lawmakers of troubled projects and force the Pentagon to formally reaffirm the program’s rationale or face its termination.

 “New information has emerged about factors that are driving changes to important aspects of the program, from the cost of materials and labor for the design and timeframe needed to build the launch facilities,” Andrew Hunter, the Air Force’s acquisition chief, said in a statement to Bloomberg News.

“We’re in a different world now than when program costs and schedules were originally set as a baseline” in August 2020, Hunter said. “Revisiting our assessments ensures senior leaders are equipped with updated information required to make decisions,” he said.

Although the Sentinel program is seen as a key deterrent against China, any major delay or cost increase may embolden arms control advocates such as Democratic Senator Elizabeth Warren who have pressed for its termination in favor of extending the life of Minuteman III missiles.

The Air Force review will take about 45 days before a determination is made as to whether the ICBM program exceeds the law’s cost thresholds, the service said in a statement.

If the Air Force and Pentagon conclude the new cost numbers will exceed the law’s thresholds, the service must inform Congress and conduct a major assessment as to whether the program should survive or face termination. To continue, the Pentagon would probably have to request more funds to cover the projected cost increase — triggering a major new debate.

One of the biggest challenges is the mammoth cost of construction and materials transportation to convert 450 Cold War-era Minuteman III missile launch facilities and 24 launch centers for Sentinel installation. This task, “estimated to last nearly 10 years, will be a lengthy and complicated process involving real estate purchases, construction, deconstruction, removal and installation of equipment and nuclear certification,” the Senate Armed Services Committee said in its fiscal 2024 budget report.

Additionally, the project will require installing more than 7,500 miles (12,000 kilometers) of underground fiber cable connecting silos constructed across US missile wings, spanning five states.

Depending on what costs are included, the current benchmark estimates range from $75 million to $118 million per missile today. For example, the $118 million figures reflect what’s  known as the “Program Acquisition Unit Cost” — or the total cost of development, procurement and construction divided by the number of units to be purchased.