Originally Posted by
Asturias56
Greta graph - but Interesting that the merchant ship losses were already falling rapidly from the peak of Q2 1942 well before the introduction of the support groups and escort carriers - even though the number of U Boats on duty went up considerably.
Something else, probably SIGINT, must have been the main reason for the fall in losses.
The graph was from an article about the Western Approaches Training Unit - which analysed tactics, devised responses to attacks, and taught the new tactics to ships' captains and others. It had a major effect. Additionally throughout 1941, even before the United States was in the war, the US Navy was escorting convoys half way across the Atlantic, which made life harder for the U boats. Add to that the impact Bomber Command had on U boat construction, and as you say ULTRA.
Other technologies were maturing as the war progressed - High Frequency Direction Finding, Radar sets small enough for escort ships and able to detect a surface U boat, more advanced ASDIC, ASW weapons such as Hedgehog, ASV radar in aircraft, the Leigh Light, and VHF radio that allow ships to talk to each other in real time as they mounted a counter attack.