U-boat

U-boats are naval submarines operated by Germany, including during the First and Second World Wars. The term is an anglicized form of the German word U-Boot [ˈuːboːt] ^ⓘ, a shortening of Unterseeboot (lit. 'under-sea boat'). Austro-Hungarian Navy submarines were also known as U-boats.

U-boats are most known for their unrestricted submarine warfare in both world wars, trying to disrupt merchant traffic towards the UK and force the UK out of the war. In World War I, Germany intermittently waged unrestricted submarine warfare against the UK: a first campaign in 1915 was abandoned after strong protests from the US but in 1917 the Germans, facing deadlock on the continent, saw no other option than to resume the campaign in February 1917. The renewed campaign failed to achieve its goal mainly because of the introduction of convoys. Instead the campaign ensured final defeat as the campaign was a contributing factor to the entry of the US in the First World War.

In World War II, Karl Dönitz, supreme commander of the Kriegsmarine's U-boat arm (Befehlshaber der Unterseeboote), was convinced the UK and its convoys could be defeated by new tactics, and tried to focus on convoy battles. Though U-boat tactics initially saw success in the Battle of the Atlantic, greatly disrupting Allied shipping, improved convoy and anti-submarine tactics such as high-frequency direction finding and the Hedgehog anti-submarine system began to take a toll on the German U-boat force. This ultimately came to a head in May 1943, known as Black May, in which U-boat losses began to outpace their effect on shipping.

A more advanced submersible, the three-man Brandtaucher, was designed by Wilhelm Bauer in 1850 and constructed by Schweffel and Howaldt in Kiel. It was lost on 1 February 1851 during a test dive.

Some 50 years later in 1903, the Friedrich Krupp Germaniawerft dockyard in Kiel completed the first fully functional German-built submarine, Forelle, which Krupp sold to Russia during the Russo-Japanese War in April 1903.

At this time, the German commander of the Navy Alfred von Tirpitz was building the High Seas Fleet with which he intended to challenge the supremacy of the UK Royal Navy. He focused on expensive battleships and there was no role for submarines in his fleet.

Only when Krupp received an order for three Karp-class U-boats from Russia, did Tirpitz order one submarine. The SM U-1 was a completely redesigned Karp-class and when the Imperial German Navy commissioned it on 14 December 1906, it was the last major navy to adopt submarines.

The U-1 had a double hull and a single 45 cm (18 in) torpedo tube. It used an electric motor powered by batteries for submerged propulsion and a Körting kerosene engine for charging the batteries and propulsion on the surface. The 50%-larger SM U-2 was commissioned in 1908, had four 45 cm torpedo tubes and a much larger battery capacity. But the boat was a failure due to problems with both the kerosene and electrical engines. The next two U-boats of the Type U 3-class, ordered on 13 August 1907, were more reliable.