The U.S. Government Accountability Office (GAO) has now released a public version of a classified report released in June that found that 10 years of maintenance delays to U.S. Navy submarines have resulted in over 15,000 lost operational days and an estimated $3.4 billion in costs.  U.S. Navy attack submarine depot maintenance delays, length of depot maintenance periods, and idle time, FY 2016–2025      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.   GAO found that 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.     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.     According to the U.S. Navy, says GAO, 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. In compiling its report, GAO analyzed U.S. Navy attack submarine maintenance data from fiscal years 2016 through 2025, reviewed U.S. Navy documentation, and interviewed officials.       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.      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. 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.