Submarine losses consumed trained crews

A sinking surface ship often left sailors in the water where friendly vessels could rescue them and return at least some to service. A submarine was usually already below the surface when destroyed, leaving its crew little chance to escape. Survivors who reached the surface were likely to become prisoners rather than resume operations. Heavy-bomber crews provide a useful comparison because losing the aircraft normally meant losing the trained team with it. Boat losses therefore tended to remove trained men from future operations as well as destroy the equipment.