A U-boat (from the German unterseeboot) is a German submarine. It was used in warfare during both World War I and World War II. These U-boats struck fear in the hearts of many, as they (during certain times) sank both military and civilian ships alike as well as ships from neutral countries.
U-boats had similar success in the first months of World War II. The aircraft carrier HMS Courageous was sunk by a German submarine on September 12, 1939, and the carrier Ark Royal narrowly missed a similar fate 2 days later. The Kriegsmarine scored an even greater victory in October, when U-47 penetrated the Royal Navy base at Scapa Flow and sank the WWI-era battleship Royal Oak.
During World War II, U-boats were primarily used to destroy the Allied transport vessels supplying the United Kingdom, as part of the Battle of the Atlantic, with the aimof causing supply shortages and forcing Britain to surrender. At first this was highly successful, but the Allies later developed many countermeasures, such as properly organised escorts, the Magnetic Airborne Detector that detected the change in local magnetic field caused by the U-boats, the 'Huff-Duff' system that tracked U-boats by their radio transmissions and improvements in depth-charges.
The primary weapons of U-boats were torpedoes.
- Submarine Warfare, an Illustrated History, by Antony Preston, Thunder Bay Press, 1998