The submarine war began on the third day of the war when a German submarine U-30 commanded by Lieutenant Fritz Julius Lemp fired on the British passenger liner Athenia. The Athenia sunk the next day, after most of the passenger were saved. One hundred and twelve people lost there lives, including 28 Americans. Lemp fired despite explicit orders not to fire on a passenger ship. In the first four months of the war 221 ships of more than 750,000 tons were sunk.
On the evening of September 17, German U-boat 29 under the command of Commander Otto Schuart fired three torpedoes at the HMS Courageous. Within fifteen minutes the Courageous sank taking with it its captain and 518 men.
On October 13th Lieutenant Gunter Prien commanding U-boat 47 successfully entered into the British naval base at Scapa Flow. There he was able to attack the British battleship Royal Oak. He first fired four torpedoes at the battleship.; Only one hit, that one doing most of its damage above the waterline. Prien returned to fire three more torpedoes. One of them causing a catastrophic explosion sinking the Royal Oak and 833 men in fifteen minutes.
The period between July and October 1940 became know as the “Happy Time” for German submarines. During this period the wolf pact, a group of submarines operating together on a convoy, became operational. U-boats reached an outstanding 217 ships sunk representing more then a million tons of shipping, losing only six U boats.
1941 saw the tide of U-Boat activities shift temporarily. The use of additional escorts, air patrols, and US convoying of ships halfway across the Atlantic significanly cut down U-Boat losses. The period that followed the American entry into the war however temporarily changed this. Suddenly there were hundreds of unescorted vessels off the coasts of the US all silohetted nicely against the lights of US cities.
By early 1943 the tide tunred decisively agaisnt the U Boats, The allies had 500 escorts at there dsiposal, they were intercepting U Boat radio communications, and the introducation of escort carriers allowed uniterrupted air coverage for convoy across the Atlantic. Thus by mid 1944 one U boat was being lost for every allied ship sunk. The war in the Atlantic would go on, but victory was in the hands of the Allies.
By the time the war had ended the U-boats had sunk 3,500 merchant vessels, costing the lives of 36,000 merchant seamen, in addition they sunk 175 warships with the lost of life of 36,200 sailors. 783 U-bots were sunk killing 30,000 German sailors.