WORLD WAR II FROM A TO Z
U-boat is the anglicised version of the German word U-Boot, a shortening of Unterseeboot, literally “undersea boat”. Although at times they were efficient fleet weapons against enemy naval warships, they were most effectively used in an economic warfare role (commerce raiding), enforcing a naval blockade against enemy shipping. The primary targets of the U-boat campaigns in both wars were the merchant convoys bringing supplies from Canada, the British Empire, and the United States to the islands of the United Kingdom and (during the Second World War) to the Soviet Union and the Allied territories in the Mediterranean.
During World War II, U-boat warfare was the major component of the Battle of the Atlantic, which lasted the duration of the war. Germany had the largest submarine fleet in World War II, since the Treaty of Versailles had limited the surface navy of Germany to six battleships (of less than 10,000 tons each), six cruisers and 12 destroyers. Hmm I guess Hitler found himself a loophole by going undersea.
Because speed and range were severely limited underwater while running on battery power, U-boats were required to spend most of their time surfaced running on Diesel engines, diving only when attacked or for rare daytime torpedo strikes. The more ship-like hull design reflects the fact that these were primarily surface vessels which had the ability to submerge when necessary. This contrasts with the cylindrical profile of modern nuclear submarines, which are more hydrodynamic underwater (where they spend the majority of their time) but less stable on the surface. Indeed, while U-boats were faster on the surface than submerged, the opposite is generally true of modern subs. The most common U-boat attack during the early years of the war was conducted on the surface and at night. This period, before the Allied forces developed truly effective antisubmarine warfare (ASW) tactics, which included convoys, was referred to by German submariners as “die glückliche Zeit” or “the happy time.”
The U-boats’ main weapon was the torpedo, though mines and deck guns (while surfaced) were also used. By the end of the war, almost 3,000 Allied ships (175 warships; 2,825 merchant ships) were sunk by U-boat torpedoes.