Wikimedia Commons
Named the “Battle of the Atlantic,” by Winston Churchill, the course of the WWII six-year U-boat campaign changed constantly, with one side or the other gaining advantage, as each side developed new weapons, tactics, counter-measures and equipment. By the end of 1942, the Allies were gradually gaining the upper hand.
When the U.S. finally instituted a convoy system in mid-1942, losses to U-boats were markedly reduced and the “second happy time” along the Eastern seaboard of America came to an end. In July 1942 Admiral Karl Dönitz ordered the withdrawal of all U-boats from the United States Atlantic coast and shifted attention back to the North Atlantic. There wolf packs of 10-15 U-boats began attacking multiple convoy routes in mid-Atlantic “air gaps” where convoys lacked aircraft support.
In the fall of 1942, convoy losses sharply increased. But so did U-boat losses. While just 21 U-boats were lost in the first half of 1942, 60 went down in August-September 1942 – one for every 10 merchant ships sunk.
U-boats lost; Wikimedia Commons
WW2 U-boat found with ship it sank off North Carolina:
https://www.bbc.com/news/world-us-canada-29721118
This New York Times excerpt from March 1942 shows how much in error American analysis of the U-Boat problem was at that time.
“It has been obvious since the start of the submarine campaign in the Western Atlantic that the objective of the Axis is not so much to destroy Allied merchant ships as to frighten America into convoying coastwise shipping and calling home naval vessels for this purpose. As long as America refuses to be frightened by these sinkings off her coast, the submarine will have failed in its major objective and sooner or later, must be abandoned as too costly for results obtained.”
New York Times
March 23, 1942