1943 Event Germany begins withdrawing U-boats from North Atlantic in anticipation of the Allied invasion of Europe 1942 Event 98 U-boats sunk this month (485,000 tons) 1942 Event German U-boats begin harassing shipping on U.S. east coast 1941 Event 53 U-boats sunk this month (202,000 tons) 1941 Event 23 U-boats sunk this month (80,000 ton) 1941 Event 61 U-boats (310,000 ton) sunk this month 1940 Event 59 U-boats sunk this month (295,000 tons) 1940 Event 56 U-boats sunk this month (268,000 ton) 1940 Event 58 U-boats (284,000 ton) sunk this month 1939 Event 41 U-boats sunk this month (153,000 ton) 1917 Event Germany notifies U.S. that U-boats will attack neutral merchant ship
