Submarines as high-value but fragile wartime assets

The X-craft passage leads into a broader force-readiness point. Submarines operate in the condition that surface ships are designed to avoid, so a single accident or defect can lead rapidly to the loss of the boat. Repeated pressure cycles and the strains associated with crush depth also make submarines depreciate faster while demanding more complicated maintenance and training. The result is that a navy cannot generate the same operational capability from a given number of submarines as from the same number of surface ships. Wartime damage magnifies the problem, as the Battle of the Atlantic demonstrated: damage that may be minor above water can become catastrophic below it.