By the time cruiser submarines appeared, convoy warfare had already proved its value in the First World War. Its rapid adoption again in the Second World War showed how familiar navies were with the system. A submarine attacking a convoy could therefore find itself exchanging gunfire with armed escorts. Its low profile and limited range-finding capability would complicate the action, while movement in the water made aiming harder. An escort might also bring more powerful guns to the encounter. These conditions weakened the expectation that the submarine could raid without effective surface opposition.
Notable Point · 3:21-4:12
Convoys undercut gun-armed raiders
Convoys exposed a surfaced gun-armed submarine to escort fire, while its low position in the water limited range finding.