U-boat technology was used to attack shipping by Germany during World War I. It threatened British civilians and war materiel production. U-boats were small and submerged targets that were difficult to attack and detect. They were effective until radar came along. However, radar was not yet a technology that was widely used by U-boat captains in the first stages of World War II.
U-boats were used to hunt convoys by the German Navy, as well combat vessels and civilian shipping. When convoys could no longer be escorted, the U-boats shadowed them and attacked at night. Most U-boats were submerged by mines or depth charges. The U-boats were able to achieve great success in the Indian Ocean.
To break through the British blockade, the German Navy constructed larger U-boats. U-boats were faster than their predecessors and had more battery capacity. They could also stay submerged for longer than their smaller predecessors.
To attack British merchant shipping, the Germans initially used U-boats. A number of attacks occurred, including the sinking of the RMS Lusitania off Ireland. U-boats were objected by the American government after it joined in the war. It had a concern that the German government's use of U-boats would lead to the breaking of diplomatic ties with the United States.
Allies were shocked by the U-boat attack on British merchant shipping. They were able to sabotage the merchant marine, which carried vital supplies to Britain. Germany could be forced to withdraw from the war by the British blockade. U-boat supply vessels were hit by the Allies' response. U-boat base bases were also targeted by strategic bombing. This method of anti-submarine warfare became known as the Battle of the Atlantic. The Allies' strategy was attack U-boat supply vessels and put all their shipping in convoys. This tactic proved less effective, however, because convoys made it difficult for the U-boats to locate targets.
German U-boats began hunting in groups, known as wolfpacks. They attacked convoys, military ships, and other vessels in the night, when there was not much air cover. They attacked both civilian and military shipping. They were also effective because of the huge gap in mid-Atlantic air cover.
The German government reacted to the U boat attacks with more U boats in the North Sea. It also ordered that the navy follow Prize Rules. This order was issued to curb U-boat activity through the war. U-boats were returned to the coast waters close to the British Isles. They were also called "wolfpacks" because they were made up several U-boats that were closely connected.
While the German government did agree to stop attacking passenger liners, it used U-boats to attack merchant shipping and civilian vessels. U-boats had destroyed more than 30% of world's merchant vessels by the end. This was the highest number of casualties suffered by any German force in the war.