Figures.

This is coolbert:

Before May 1943 the German U-boat campaign in the Atlantic during World War Two [WW2] effective. In the aftermath of May 1943 the German U-boat effort more or less an insignificant factor in the war if not a total failure.

As excerpted from "The Reader's Companion to Military History" article by Holger H. Herwig the topic German WW2 Admiral Karl Doenitz; the German U-boat campaign, success and ultimate disaster:

"Donitz commanded Germany's U-boat forces in the Battle of the North Atlantic. His submarines sank 175 Allied warships and 2,603 merchant ships but lost 784 boats and 28,000 men. In April 1943 Convoy HX231 drove off all attacking U-boats. Allied convoys, radar, aerial patrols, depth charges, special naval 'killer groups,' and Ultra electronic intercepts blunted the German underseas campaign. Donitz conceded defeat in the battle on May 23, 1943, when he recalled his boats. After 1943  more than thirty-five hundred Allied ships in sixty-two convoys crossed the Atlantic without a single loss."

Those various convoys after May 1943 in totality by my calculations carrying enough war-making munitions alone to supply and equip an army of about five million men.

Eighty percent of German submariners losing their lives during the war!! A submarine sinking as you can well imagine the loss of life 100 % in almost all cases.

coolbert.