Shipyard limits and the backlogThe maintenance backlog is driven by the capacity limits of the four US public shipyards: Norfolk, Portsmouth, Puget Sound, and Pearl Harbor. Compounding this is the strict control of technical data rights by the two private companies building Virginias, which introduces administrative delays when public shipyards attempt to source components or access software. Shipyard personnel face sustained overtime rates between 25 per cent and 32 per cent, periodically spiking to 45 per cent. The US submarine industrial base currently produces Virginia-class hulls at a rate of 1.1–1.2 vessels per year. Personnel numbers and experience levels in the shipyards and submarine crews remain understrength and heading in the wrong direction.