Sentinel ICBM (LGM-35A): the 81% Nunn-McCurdy Breach
The US Air Force’s Sentinel intercontinental ballistic missile, which replaces the 1970s Minuteman III, saw its program acquisition cost estimate rise from about 77.7 billion USD at its 2020 baseline to roughly 141 billion after a 2024 Pentagon review. The 81% per-unit growth triggered a critical Nunn-McCurdy breach and forced a restructure of the largest single line item in the US nuclear-modernization plan.
How much did the Sentinel ICBM cost overrun?
Sentinel’s program acquisition cost estimate rose from about $77.7 billion (2020 baseline) to roughly $140.9 billion after a Department of Defense review completed in July 2024. Per missile, cost grew 81%, from $118 million to about $214 million. That 81% growth triggered a critical Nunn-McCurdy breach in January 2024; the Pentagon certified the program to continue but rescinded its Milestone B approval and ordered a restructure.
How the breach unfolded
- January 2024: critical Nunn-McCurdy breach. The Air Force notified Congress that Sentinel’s per-unit cost had grown about 37% over its baseline, tripping the “critical” threshold and forcing a mandatory Department of Defense review.
- July 2024: certified, but restructured. The review found 81% program acquisition unit cost growth against the original baseline. Rather than cancel, the Pentagon certified the program to Congress as essential to national security, put the revised estimate at about $140.9 billion, rescinded Milestone B approval, and ordered the Air Force to restructure and scale back the launch facilities.
- The command and launch segment is the driver. DOD acquisition chief William LaPlante said most of the overrun came not from the missile but from the command and launch segment, the missile silos and launch control centers. Sentinel modernizes more than 600 facilities across five states, and the civil-engineering scale of that work was badly underestimated.
- February 2026: software lag and schedule slip. GAO reported that software progress had fallen behind, with the design, development metrics, and delivery schedule not yet finalized. The first flight test has slipped about four years to March 2028.
- Minuteman III must soldier on. Because of the delay, the Air Force may need to keep the aging Minuteman III operational until around 2050, roughly 14 years beyond the original plan, creating sustainment and testing challenges of its own.
Why it matters for cost-overrun analysis
Sentinel is a textbook infrastructure-underestimation overrun dressed as a missile program. The rocket itself is a relatively conventional solid-fuel ICBM; the cost blew out in the ground segment, where rebuilding hundreds of hardened 1970s launch facilities across five states behaved like a sprawling civil-construction megaproject rather than a defense procurement. That is the same failure mode Bent Flyvbjerg documents across infrastructure: the visible, exciting object is scoped carefully while the boring, buried civil works that dominate the budget are estimated last and worst.
In GAO’s 2025 assessment, Sentinel alone accounted for $36 billion (73%) of the $49.3 billion one-year rise in combined cost estimates across 30 continuing major defense programs, making it the single largest driver of US weapon-system cost growth in that year.
Sources
- GAO Weapon Systems Annual Assessment 2025 (GAO-25-107569): source of the $36bn Sentinel share
- GAO Weapon Systems Annual Assessment 2026 (GAO-26-108457)
- Congressional Research Service, Defense Primer: LGM-35A Sentinel ICBM (IF11681)
- US Department of Defense statement on completion of the Sentinel Nunn-McCurdy review (William LaPlante), 8 July 2024: revised estimate ~$140.9bn, 81% unit-cost growth, Milestone B rescinded.
Cost figures are program acquisition cost estimates; per-unit figures are program acquisition unit cost (PAUC). The $118M baseline is in 2020 dollars. Verified July 2026.