The U.S. Air Force’s troubled Sentinel intercontinental ballistic missile program faces significant risks from software delays and an extended reliance on the aging Minuteman III system.
However, a January 2024 Nunn-McCurdy breach has opened a window to address longstanding issues and potentially improve outcomes, according to a Government Accountability Office snapshot released Feb. 18.
The report highlights the challenges in replacing the 50-year-old Minuteman III, a cornerstone of the land-based leg of the U.S. nuclear triad, with the more advanced Sentinel system.
The program, led by Northrop Grumman, is described as the Air Force’s most complex infrastructure endeavor ever, involving the replacement of more than 600 facilities across five states, including missile silos and command centers.
The Sentinel program encountered a critical setback in 2024, when it triggered a Nunn-McCurdy unit cost breach, exceeding statutory thresholds for cost growth on major defense acquisitions.
This led the under secretary of defense for Acquisition and Sustainment to rescind Milestone B approval and associated baselines, forcing a restructuring effort as the service works toward a new Milestone B decision.
The program’s estimated cost is now at least $141 billion, though actual figures remain uncertain. The first Sentinel flight has slipped approximately four years and is now planned for March 2028.
Software development stands out as a major risk area. The report notes that Sentinel is highly software-intensive, and progress has lagged behind expectations.
“These delays have raised concerns from program officials about the prime contractor’s ability to complete the program’s software in a timely manner,” GAO states.
Despite years in development, the Air Force and contractor have yet to finalize software design, development metrics or a delivery schedule, prompting a replan.
While disruptive, the breach has created opportunities for course correction. GAO emphasizes that restructuring allows the Air Force to address fundamental problems, including deficiencies in design tools, performance requirements and launch facility design.
Program officials are evaluating redesign options for portions of the weapon system to reduce costs and minimize further schedule slips, as well as potential changes to acquisition strategy and system requirements.
“Future program outcomes will depend on the extent to which the Air Force takes advantage of this opportunity to correct earlier missteps,” the report warns.
Sentinel is expected to deliver a significantly more capable ICBM, with a modular design that enables adaptation to evolving threats and technologies.
However, Sentinel delays may require Minuteman III to remain operational through 2050, 14 years beyond original plans, introducing sustainment and testing challenges for the aging fleet.
Air Force and defense officials told GAO they are actively mitigating risks to prevent any capability gaps during the transition.
GAO highlights risks in parts supply for continued annual flight tests and the absence of a comprehensive transition risk management plan, a key leading practice for such megaprojects.
The service has developed an overarching transition strategy but lacks detailed risk tools to systematically identify, assess and respond to issues, the report states.
The snapshot cites prior GAO recommendations from 2025, urging the Air Force to develop a transition risk management plan (including Minuteman III sustainment), a post-2030 operational test launch plan aligned with Sentinel fielding and a strategy for Sentinel launch facility testing to inform security policy updates.
Overall, the report portrays an extremely risky, high-stakes modernization megaproject, but restructuring offers a chance to bolster project management and deliver a more adaptable deterrent without compromising nuclear readiness.