The U-boat Campaign Military_operation from 1915 to 1918 was the World War I naval campaign fought Hostile_encounter by German U-boats against the trade routes of the Allies .

In the course of events in the Atlantic alone , German U-boats sank Attack almost 5,000 ships with nearly 13 million gross register tonnage , losing Earnings_and_losses 178 boats and about 5,000 men in combat .

Other naval theatres saw U-boats operating in both the Far East and South East Asia , the Indian Ocean and the Mediterranean and North Seas .

Two U-boats were sunk near the carriers by British patrol aircraft and several others were damaged Damaging .

The outcome of the battle Hostile_encounter was a strategic victory Earnings_and_losses for the Allies—the German blockade failed—but at great cost Cost : 3,500 merchant ships and 175 warships were sunk Earnings_and_losses in the Atlantic for the loss Earnings_and_losses of 783 U-boats ( the majority being Type VII submarines ) and 47 German surface warships , including 4 battleships ( `` Scharnhorst '' , `` Bismarck '' , `` Gneisenau '' , and `` Tirpitz '' ) , 9 cruisers , 7 raiders , and 27 destroyers .

Of the U-boats , 519 were sunk Motion by British , Canadian , or other allied forces Causation , while 175 were destroyed Destroying by American forces Causation ; 15 were destroyed Destroying by Soviets and 73 were scuttled Destroying by their crews before the end Process_end of the war Hostile_encounter for various causes .

The Allies gradually gained Getting the upper hand , overcoming Conquering German surface raiders by the end Process_end of 1942 and defeating Conquering the U-boats by mid-1943 , though losses Earnings_and_losses due to U-boats continued until the war Hostile_encounter 's end Process_end .

The Allies gradually gained Getting the upper hand , overcoming Conquering German surface raiders by the end Process_end of 1942 and defeating Conquering the U-boats by mid-1943 , though losses Earnings_and_losses due to U-boats continued until the war Hostile_encounter 's end Process_end .