WASHINGTON — The Air Force’s next nuclear missile program has exceeded its planned costs severely enough to trigger a report to Congress, potentially putting the program’s survival at risk.

The Northrop Grumman-made LGM-35A Sentinel intercontinental ballistic missile has overrun its initial cost projections and incurred a critical Nunn-McCurdy breach, an Air Force spokesperson confirmed to Defense News. The Air Force notified Congress about the breach Thursday.

The Office of the Secretary of Defense will now review the Sentinel program, the Air Force said, and will decide whether to restructure the program, or cancel it entirely.

“Work under the current contract will continue until OSD completes its review of the Sentinel program,” the Air Force spokesperson said. “Maintaining a strong nuclear deterrent is critical to safeguarding our nation and protecting our allies from a nuclear attack.”

The Sentinel program is planned to replace the Air Force’s Cold War-era LGM-30G Minuteman III ICBM as part of the U.S. nuclear triad. Northrop Grumman in 2020 received a $13.3 billion contract to build Sentinel, and the program was originally expected to cost about $96 billion.

The per-unit total cost for the Sentinel was $118 million when the program’s cost, schedule and performance goals in 2020, the Air Force said. Since then, that has grown at least 37% to about $162 million, triggering this cost overrun process.

A critical Nunn-McCurdy breach is declared when a major defense acquisition program’s cost grows 25% over the current cost targets or at least 50% over the original cost. The Defense Department must notify Congress when such a major cost overrun occurs and certify the program is essential to national security and must continue.

The Pentagon will also have to certify to Congress that there are no cheaper alternatives to the Sentinel program, that the new cost estimates are reasonable, that it is a higher priority than other programs whose funding could be cut to cover the cost growth, and that the program’s management structure can control further cost growth. If that certification does not happen, the program would be terminated.

William LaPlante, the undersecretary of defense for acquisition and sustainment, said in a statement that “Sentinel is one of the department’s largest, most complex programs” and the Pentagon has taken several steps to help it.

Defense Secretary Lloyd Austin in December 2022 declared the Sentinel program one of the Pentagon’s most important and gave it priority in the supply chain, LaPlante said. He also said that in 2023 he approved changes to its acquisition strategy meant to keep it on schedule.

“We are prepared to fulfill the department’s statutory responsibilities [in light of the Nunn-McCurdy declaration] and conduct a robust review of the program to determine what factors caused the cost growth,” LaPlante said. “As we do so, we will keep our partners in Congress informed and maintain open communications to the greatest extent possible.”

Northrop Grumman, the prime contractor on Sentinel’s engineering and manufacturing development phase, said in a statement to Defense News it is making “significant progress” on the program and reaching milestones to mature its design and reduce risk.

“As part of our work on the EMD contract, our team is committed to supporting the Air Force as it assesses and updates acquisition cost forecasts for the future phases of the program, to include construction projects, production, and deployment of the weapon system,” Northrop Grumman said. “We are focused on continuing to perform and meet our commitments under the EMD contract as we move toward delivery of this essential national security capability.”

The date Sentinel might reach initial operational capability also is now likely to slip by two years, the Air Force said. Sentinel was originally expected to reach IOC in 2029. The Government Accountability Office warned last year that deadline would likely slip until about spring 2030, and the program now appears to be falling further behind schedule.

The Air Force said the IOC delay will also be reviewed as part of the Nunn-McCurdy process.

The service noted the bulk of Sentinel’s cost growth is coming in its command and launch segment, the most complex part of the program.

This includes building more than 400 new launch facilities and laying thousands of miles of fiber optic networks, the Air Force added, as well as acquiring permanent and temporary real estate easements from hundreds of landowners.

The Sentinel program will also need to build more than 7,500 miles of utility corridors across missile wings spanning five states, the Air Force said, while keeping 400 ICBMs on alert.

The Air Force said it has not seen similarly severe cost growth in the missile itself.

Air Force Secretary Frank Kendall in November 2023 said the Sentinel program was “struggling” and its costs might rise.

Kendall called the scale and complexity of the Sentinel program “probably the biggest thing … that the Air Force has ever taken on,” highlighting the construction of launch complexes, real estate development and civil engineering work as particular challenges.