How would the Atlantic war change if Germany fielded Type XXI submarines in late 1942 or 1943?
Short answerAllied anti-submarine work would become much harder and more resource-intensive, but the Type XXI would not automatically restore decisive German success.
NotesThe Type XXI's submerged performance and snorkel would reduce the long surface exposure that Allied aircraft and escorts exploited. Britain and the United States would have to devote more effort to anti-submarine warfare and operate with less confidence. A renewed surge in convoy losses would not be automatic because firing still reveals a submarine's presence and brings escorts into the hunt. Even an advanced wartime submarine has less sustained endurance than the surface forces protecting a convoy, so improved U-boats change the contest without guaranteeing victory.