A submarine victory could still lose the exchange

The Red Sea encounters expose an unfavorable replacement exchange even when an Italian submarine struck first. Surface escorts often recovered most of a damaged sloop or destroyer's crew, whereas a lost submarine usually took its trained crew with it or left survivors as prisoners. Replacing a small escort was therefore easier than replacing an isolated submarine and its specialist personnel. Submarines are ambush predators with a glass jaw once they reveal themselves, so a supporting force and a planned withdrawal route are part of their combat effectiveness.