During World War I, Germany used U-boat technology to attack shipping, threatening the British population and production of war materiel. U-boats were small, submerged targets, and were difficult to detect and attack. Until the advent of radar, they were effective. But by the early stages of World War II, radar was a new technology and many U-boat captains chose not to use their U-boat radar systems.
U-boats were used in the German Navy's hunt for convoys. 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. However, the Uboats had some success in India Ocean.
The German Navy designed larger U.boats to break the British blockade. U-boats had greater speed and battery power, which allowed them to travel faster. They could stay submerged for longer periods than their smaller predecessors.
To attack British merchant shipping, the Germans initially used U-boats. There were several attacks, including that of the RMS Lusitania (off Ireland). U-boats were opposed by the American government, which joined the war. It was concerned that U.boats could be used by the German Government to break diplomatic ties with the United States.
Allies were shocked by the U-boat attack on British merchant shipping. They were capable of destroying the merchant marine, which supplied vital supplies to Britain. Germany would be starved if the British blocked access to its ports. U-boat supply vessels were hit by the Allies' response. U-boat bases were also attacked with strategic bombardment. This form of anti-submarine warfare was known as the Battle of the Atlantic. The Allies' strategy was to attack U-boat supply vessels, while putting all of their shipping into convoys. However, this tactic was less successful because U-boats had difficulty finding targets due to the convoys.
German U-boats began hunting in groups, known as wolfpacks. They attacked convoys as well as military ships at night, when air cover was limited. They also sank passenger liners and civilian shipping. They were also successful because of the large gap in midatlantic air coverage.
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 aimed at restraining U-boat activities until the end of the war. U-boats returned from the war to coast waters near the British Isles. They were also called wolfpacks because they were composed of several U-boats closely together.
Although the German government accepted to stop attacks on passenger lines, it continued to use U boats against merchant shipping and civilian ship. The U-boats had already sunk over 30% of all world merchant ships by the end of World War II. This was the highest rate of casualties of any German force during the war.