US Submarine Fleet Loses 15,000 Operational Days as Maintenance Delays Deepen

The US Navy’s attack submarine force is facing a serious readiness challenge as prolonged maintenance delays and limited dry-dock capacity continue to keep vessels away from operational duties. A new assessment by the Government Accountability Office (GAO) estimates that more than 15,000 operational days have been lost over the past decade, highlighting the growing strain on the infrastructure needed to maintain America’s nuclear-powered attack submarines.

The problem is not simply the amount of time submarines spend undergoing repairs. Some boats remain alongside piers waiting for a maintenance slot because shipyards lack sufficient capacity. During this period, submarines and their crews can remain unavailable for normal missions, reducing the number of vessels that can be deployed when required.

According to the GAO, these delays between fiscal years 2016 and 2025 have generated an estimated $3.4 billion in costs. The spending includes supporting submarines and crews during periods when the vessels were unable to provide operational capability.

Dry-Dock Capacity Emerges as a Major Bottleneck

America’s attack submarine fleet depends on specialised shipyards for complex maintenance work. The Navy currently carries out this work at four public shipyards: Norfolk Naval Shipyard in Virginia, Portsmouth Naval Shipyard in New Hampshire, Puget Sound Naval Shipyard in Washington and Pearl Harbor Naval Shipyard in Hawaii.

The shortage of available dry-dock capacity has contributed to submarines waiting extended periods before repairs can even begin. In some cases, vessels have reportedly spent years waiting for the maintenance process to move forward.

The consequence is a gap between the number of submarines officially belonging to the fleet and the number that can actually perform missions. Attack submarines are particularly important to US military planning because they can conduct intelligence operations and strike missions while operating with a high degree of stealth.

Readiness Impact Remains Significant

The Navy’s attack submarine force includes Los Angeles-class and Virginia-class vessels. The GAO found that maintenance delays have reduced the operational availability of these boats, creating a readiness problem that could become more consequential as demands on the fleet increase.

The report noted that the Navy has made progress in reducing what is known as “active idle time.” This refers to situations in which submarines and their crews remain at the pier because the vessels are no longer certified for normal operations but cannot yet enter a maintenance period. Between 2023 and 2025, the Navy reduced this waiting time, representing an improvement despite the wider backlog.

In 2025 alone, the Navy lost the operational equivalent of roughly two attack submarines when active idle time and maintenance delays were combined. The figure represented 753 days of lost operational availability. The impact had been even larger in 2023, when the lost time was equivalent to about five submarines.

A Second Problem Is Growing

While the Navy has reduced active idle time, the GAO has identified another concern involving submarines approaching retirement.

Boats scheduled to be decommissioned can also become stuck waiting for shipyard capacity. Before a nuclear-powered submarine can be dismantled, its reactor must be defueled, a process requiring specialised facilities.

The GAO estimates that 15 attack submarines could enter this type of inactive idle period between fiscal years 2026 and 2030. Without corrective measures, these vessels could collectively accumulate more than 14,000 days of inactive idle time, potentially costing the Navy another $3.1 billion in operating and support expenses.

This creates an unusual situation in which shipyard congestion can affect both submarines that the Navy wants to keep operating and older vessels that are waiting to leave service.

China Adds Pressure to the Challenge

The maintenance backlog comes at a particularly important time for the US Navy. American attack submarines are widely regarded as a major component of the country's military advantage, particularly in the Indo-Pacific where the US is increasingly focused on China's expanding naval capabilities.

China has been rapidly increasing its shipbuilding capacity and expanding its naval forces. Against this backdrop, maintaining a reliable pool of deployable US submarines has become increasingly important.

The GAO's findings therefore point to an issue extending beyond shipyard efficiency. If submarines spend too much time waiting for repairs, the Navy effectively has fewer boats available for patrols, deterrence missions, intelligence gathering and other operations.

Pressure on the US Shipbuilding System

The maintenance difficulties also form part of a broader challenge facing the US Navy's industrial base. The service is simultaneously dealing with the construction of new submarines, the retirement of ageing vessels and the maintenance requirements of the existing fleet.

The GAO's assessment suggests that increasing construction alone will not solve the readiness problem. Existing submarines also require timely maintenance, while retired vessels need to move efficiently through the decommissioning process.

For the Navy, expanding and modernising shipyard capacity will therefore remain a crucial part of strengthening the submarine force. The recent reduction in active idle time provides some evidence that improvements are possible, but the underlying maintenance backlog remains unresolved.

The latest findings underline a fundamental challenge for the US undersea fleet: having advanced submarines is not enough if too many are waiting on the pier or in shipyards instead of being available for missions at sea.