A navy's nominal ship count is larger than the force it can keep available for operations. As a rule of thumb, one third of its ships may be in maintenance and another third training or travelling. Combat damage and losses reduce the operational fraction further. During periods when the US Navy concentrated destroyers in the Pacific, Canadian escorts could outnumber American naval escorts on Atlantic convoys, and the US Coast Guard could contribute more vessels than the US Navy. These examples connect convoy contributions with competing commitments and the cumulative effect of a long war.
Notable Point · 1:55:25-1:56:46
Why fleet size overstates operational availability
Destroyer shortages reflected maintenance, transit, training, and combat losses, so coalition partners often carried more of the Atlantic escort burden.