New GAO Report: Strategic Missiles At or Below Cost, But Sentinel Faces Year Delay

The cost of the nuclear AGM-181 Long-Range Stand Off missile has come down slightly and the program is on track, but several technologies it relies on are still considered immature, the Government Accountability Office found in a report.

Meanwhile, the GAO also assessed the LGM-35A Sentinel intercontinental ballistic missile as being on cost with all its critical technologies expected to be ready on time—yet still a year behind schedule.

The developments are noted in GAO’s 2023 Weapon Systems Annual Assessments, released June 8, which report to Congress on the status of programs across the services. The LRSO and the Sentinel—USAF’s two strategic nuclear missile modernization programs—are among 14 Air Force programs included in the report.

The GAO report’s data is current as of March, so some information may be out of date.   

The LRSO, which will succeed the AGM-86B Air-Launched Cruise Missile and will be deployed on the B-52 bomber, saw a slight programmatic cost decrease since last year’s report; total predicted costs have declined from $15.1 billion in development and procurement costs to $14.9 billion, a difference of about one percent. The projected unit cost of LRSO has also come down, from an expected $13.9 million per missile to $13.75 million apiece, across an estimated purchase of 1,087 weapons.

However, GAO noted that the Air Force’s cost estimates for the nuclear missile and those of the Office of the Secretary of Defense (OSD) differ, and OSD “found procurement could cost $1.9 billion more than the Air Force estimate.”

The difference is the result of OSD using data from previous nuclear missile programs, while the Air Force used “proposed data, purchase order, and actual cost data from parts of recently-built LRSO missiles,” GAO said, apparently finding the Air Force’s numbers more convincing.

At the critical design review in February-March, OSD’s numbers were used, but the program has asked OSD to conduct another estimate in 2023, based on data from test LRSO missiles.

The GAO assessed the missile’s design as “stable.” The program started out in 2021 with what the GAO deemed “immature technologies,” and since then, two are considered mature, three are approaching maturity and one—nuclear hardness—is still considered immature. The greatest amount of immaturity in the program has to do with the nuclear warhead technologies and not the vehicle. The Department of Energy doesn’t expect to mature those elements until 2025, GAO reported. That imposes risk on the program, because starting development without demonstrating critical technologies means there could be costly work later on.

A “system-level prototype” of LRSO was tested in 2022, and the GAO said test flights of LRSO vehicles have taken place. While the Energy Department told GAO there’s a risk of an 18-month delay in warhead development, the program office will use surrogate warheads to mitigate any delays, the audit agency said.

“The Air Force plans to demonstrate missile-critical manufacturing processes on a pilot production line prior to the production decision in 2027,” GAO said. “Our prior work found this testing provides decision makers confidence that the contractor can meet quality, cost, and schedule goals.

Responding to the GAO, the program office said “LRSO development is on track for on-time fielding.”

The next big milestone for LRSO will be the low-rate production decision in mid-2027. Operational testing is slated to be complete by the end of calendar 2028 and the go-ahead for full-rate production is planned for early 2029. The Air Force won’t reveal the planned initial operational capability date due to classification, GAO said.


The Sentinel program, while still on cost, is seeing about a year’s delay, the GAO said. According to the program timeline accompanying the new report’s entry on Sentinel, initial operational capability is now expected between April and June 2030, about a year later than previous estimates, and skating close to the no-fail IOC of September 2030 required by U.S. Strategic Command.

“Sentinel is behind schedule due to staffing shortfalls, delays with clearance processing, and classified information technology infrastructure challenges,” the GAO said. “Additionally, the program is experiencing supply chain disruptions, leading to further schedule delays.”

In fact, the program’s master schedule contains “many deficiencies” and can’t be used to effectively manage the program, the GAO said, adding that contractor Northrop Grumman is reviewing the schedule and discussing how it may be changed.

The GAO also chalked up some delay to cybersecurity risk reduction activities. Cybersecurity requirements have been delayed pending the maturation of program requirements and “architecture models,” the GAO said, “resulting in schedule delays and cost growth.”

The program, which GAO called “complex,” will replace the Minuteman III ICBM as well as missile silos and the command-and-control system undergirding it. All that is estimated to cost $85.1 billion, including development, manufacture, and construction, the GAO said, noting that this estimate—dated January 2023—is exactly the same as the baseline estimate in September 2020.

The GAO said that of Sentinel’s 18 critical technologies, three are mature, 14 are approaching maturity and just one is immature, but the program expects to get all of those up to maturity before production begins in 2026.

The program has “successfully completed developmental tests of the new rocket motor and other missile components,” GAO said.

Although the digital approach taken to Sentinel’s design has been highly lauded by members of Congress and the DOD—praising the fact that it evaluated millions of alternatives before settling on an optimum configuration—GAO said the digital engineering environment for the program remains incomplete.

The environment “enables the digital integration of program’s data, tools, and model-based systems engineering activities to accelerate design and analysis,” but the fact that it’s still incomplete “is adding risk to Sentinel’s schedule, including major milestones such as system-level critical design review and first flight, both planned for fiscal year 2024.” The GAO said the digital environment was expected to reach IOC by the second quarter of fiscal 2023.

Critical design review is set for April-June 2024, with low-rate production expected exactly two years later. Operational testing will conclude in the fall of 2029, with IOC in mid-2030, and full-rate production later that year. The Air Force plans to buy 659 Sentinels, accounting for silo-deployed missiles and test units.  

The program office pointed out to GAO that “Sentinel is a total system replacement of the intercontinental ballistic missile system’s 400 missiles, 450 silos, and more than 600 facilities over a 31,900 square-mile landmass. … Sentinel is one of the top priorities within the Department of Defense, and the program has the attention and focus of the department’s senior leadership.”