Navy Readiness: Actions Needed to Address Costly Attack Submarine Maintenance Challenges
Fast Facts
The U.S. Navy's attack submarines gather intelligence undetected and attack enemy targets. 10 years of maintenance delays for these submarines have resulted in over 15,000 lost operational days and an estimated $3.4 billion in costs.
Additional delays are on the rise as submarines wait to be decommissioned—taken out of service—because shipyards don't have the capacity to start that process. With more submarines needing to be decommissioned in the next 5 years, decommissioning delays could cost the Navy more than $3.1 billion.
Finding alternative ways to reduce backlogs could save the Navy billions of dollars.
Our recommendations address this.
USS Pasadena waiting to be taken out of service
Picture of a submarine that looks like it isn't in any condition to go anywhere, tied to a pier.
Highlights
What GAO Found
The U.S. Navy has not fully mitigated attack submarine fleet maintenance and other challenges affecting readiness. Over the last 10 years, the U.S. Navy has lost more than 15,000 operational days due to maintenance delays and idle time on active attack submarines. These delays resulted in an estimated $3.4 billion in costs to sustain crews and submarines that provided no operational capability.
U.S. Navy Attack Submarine Depot Maintenance Delays, Length of Depot Maintenance Periods, and Idle Time, Fiscal Years 2016–2025
Lost operational days include delays completing depot maintenance and active idle time. Active idle time describes a period when an attack submarine and its crew must remain pier-side because they are no longer certified to conduct normal operations and cannot be inducted into a maintenance period. In addition to lost operational days, the Navy faces significant challenges with managing inactive idle time for attack submarines. Inactive idle time describes when an attack submarine designated for decommissioning cannot be inducted into a dry dock in a shipyard. As a result, the submarine and its crew must remain pier-side until a shipyard has the capacity in a dry dock to defuel their nuclear reactor.
While the U.S. Navy has made recent progress in reducing active idle time, inactive idle time for submarines has grown and is projected to worsen. Without mitigation, 15 attack submarines will enter inactive idle time from fiscal year 2026 through fiscal year 2030—during which time the Navy could incur more than 14,000 days of inactive idle time and $3.1 billion in costs to operate and support these inactive submarines. The U.S. Navy has not fully evaluated alternative options to more efficiently decommission attack submarines and develop and implement an inactivation plan that could allow them to reduce inactive idle time for crews and save billions.
Why GAO Did This Study
According to the U.S. Navy, its 44 attack submarines, as of fiscal year 2025, provide the United States an asymmetric advantage to gather intelligence undetected and attack enemy targets, among other missions. These capabilities make attack submarines some of the most requested assets by the global combatant commanders.
House Report 118-529 includes a provision for GAO to assess the readiness and availability of the U.S. Navy’s attack submarine fleet. This report discusses the extent to which the Navy has effectively maintained its attack submarine fleet and has mitigated any challenges. GAO analyzed U.S. Navy attack submarine maintenance data from fiscal years 2016 through 2025, reviewed U.S. Navy documentation, and interviewed officials.
This report is a public version of a classified report GAO issued July 16, 2026. GAO omitted information the Department of Defense deemed classified or sensitive, such as attack submarine operational availability and how the U.S. Navy’s approach to attack submarine force generation compares to strategic competitors’ approaches.
Recommendations
GAO is making two recommendations including that the U.S. Navy fully evaluate alternative options to more efficiently decommission attack submarines and develop an attack submarine inactivation plan that reduces inactive idle time. The Navy verbally concurred with GAO’s recommendations, but did not provide written comments.
Recommendations for Executive Action
| Agency Affected | Recommendation | Status |
|---|---|---|
| Department of the Navy | The Secretary of the Navy should ensure that the Chief of Naval Operations directs the Naval Sea Systems Command to fully evaluate alternative options for decommissioning attack submarines more efficiently to optimize shipyard capacity for the operational fleet. Such options may include, but are not limited to, defueling outside of dry docks and reducing crewing for attack submarines awaiting decommissioning. (Recommendation 1) |
When we confirm what actions the agency has taken in response to this recommendation, we will provide updated information.
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| Department of the Navy | The Secretary of the Navy should ensure that the Chief of Naval Operations directs the Naval Sea Systems Command to use the evaluation above to develop and implement a plan for attack submarine inactivations that reduces inactive idle time for crews and submarines. This plan should include steps to achieve objectives and timeframes for monitoring and mitigating risk for inactive idle time reduction. (Recommendation 2) |
When we confirm what actions the agency has taken in response to this recommendation, we will provide updated information.
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