The U-boat Campaign from 1914 to 1918 was the World War I naval campaign fought by German U-boats against the trade routes of the Allies. It took place largely in the seas around the British Isles and in the Mediterranean.
The German Empire relied on imports for food and domestic food production and the United Kingdom relied heavily on imports to feed its population, and both required raw materials to supply their war industry; the powers aimed, therefore, to blockade one another. The British had the Royal Navy which was superior in numbers and could operate on most of the world's oceans because of the British Empire, whereas the Imperial German Navy surface fleet was mainly restricted to the German Bight, and used commerce raiders and unrestricted submarine warfare to operate elsewhere.
In the course of events in the Atlantic alone, German U-boats sank almost 5,000 ships with nearly 13 million gross register tonnage, losing 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.