U-boat is the anglicized version of the German word , itself an abbreviation of Unterseeboot (undersea boat), and refers to military submarines operated by Germany, particularly in World War I and World War II. Although in theory, U-boats could have been useful fleet weapons against enemy naval warships, in practice they were most effectively used in an economic-warfare role, 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 the British Empire and the United States to the Island of Great Britain. Austrian submarines of World War I were also known as "U-Boats".
The distinction between U-boat and submarine is common in English-language usage (where U-boat refers exclusively to the German vessels of the World Wars) but is unknown in German, in which the term U-Boot refers to any submarine.
This was followed in 1890 by W1 and W2, built to a Nordenfelt design. In 1904, Krupp's dockyard in Kiel completed a submarine which was sold to Russia. The first works were carried out by the Spanish engineer Raymondo Lorenzo d'Equevilley Montjustin (submarine 'Narval') The first for the German Navy was built in 1905. This was the "Karp" class which had a double hull with a Körting kerosene engine and a single torpedo tube. This was designated U1, with the 50% larger U2 design having two tubes. A diesel engine was not installed in a German Navy boat until the U19 class of 1912-13. At the start of war Germany had 48 submarines in service or under construction. These were of 13 different classes.
At the start of World War I, Germany had twenty-nine U-boats in service; in the first ten weeks, five British cruisers had been lost to them. In September, U-9 sank the obsolete British warships Aboukir, Cressy and Hogue (the "Live Bait Squadron") in a matter of an hour.
For the first few months of the war, U-boat anti-commerce actions observed the current "prize rules" which governed the treatment of enemy civilian ships and their occupants. On 20 October 1914 the U-boat U17 sank the first merchant ship, the SS Glitra off Norway. Surface commerce raiders were proving to be ineffective, and on 4 February 1915, the Kaiser assented to the declaration of a war zone in the waters around the British Isles. This was cited as a retaliation for British minefields and shipping blockades. Under the instructions given to U-boat captains, they could sink merchant ships, potentially neutral ones, without warning. A statement by the U.S. Government, holding Germany "strictly accountable" for any loss of American lives, made no material difference.
On 7 May 1915, U-20 sank the liner RMS Lusitania with a single torpedo hit. The sinking claimed 1,198 lives, 128 of them American civilians, including noted theatrical producer Charles Frohman and Alfred Vanderbilt, a member of the prestigious Vanderbilt family. The sinking deeply shocked the Allies and their sympathizers because an unarmed civilian merchant vessel was attacked without any warning. According to the ship's manifest, Lusitania was carrying military cargo After further investigations, it has been confirmed that the Lusitania was in fact carrying bullets and ammunition for the allies to use against the Germans. However, this was not known at the time and the Lusitania was mistaken for a troopship. It was not until the sinking of the ferry "Sussex" that there was a widespread reaction in the USA.
The initial U.S. response was to threaten to sever diplomatic relations, which persuaded the Germans to re-impose restrictions on U-boat activity. The U.S. reiterated its objections to German submarine warfare whenever U.S. civilians died as a result of German attacks, which prompted the Germans to fully re-apply prize rules. This, however, removed the effectiveness of the U-boat fleet, and the Germans consequently sought a decisive surface action, a strategy which culminated in the Battle of Jutland.
Although the Germans claimed victory at Jutland, the British Grand Fleet remained in control at sea. It was necessary to return to effective anti-commerce warfare by U-boats. Vice-Admiral Reinhard Scheer, Commander in Chief of the High Seas Fleet, pressed for all-out U-boat war, convinced that a high rate of shipping losses would force Britain to seek an early peace before the United States could react effectively.
The renewed German campaign was effective, sinking 1.4 million tons of shipping between October 1916 and January 1917. Despite this, the political situation demanded even greater pressure, and on 31 January 1917, Germany announced that its U-boats would engage in unrestricted submarine warfare beginning 1 February. On 17 March, German submarines sank three American merchant vessels, and the U.S. declared war in April 1917.
In the end, the German strategy failed to destroy sufficient Allied shipping, largely due to the introduction of escorted convoys, before U.S. manpower and materiel could be brought to bear in France. However, the main reason for the ending of the war was the effectiveness of the British blockade of Germany which brought about an economic collapse. An armistice became effective on 11 November 1918 and all surviving German submarines were surrendered. Of the 360 submarines that had been built, 178 were lost but more than 11 million tons of shipping had been sunk.
In the early stages of the war, the U-boats were extremely effective in destroying Allied shipping, initially in the gap between Canadian and British escorts. Later when the USA entered the war the U-boats ranged from the Atlantic coast of the United States and Canada to the Gulf of Mexico, and from the Arctic to the west and southern African coasts and even as far east as Penang. It is even rumored that one German U-boat managed to make it all the way down to Galveston Bay, Texas. 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 most common U-boat attack during the early years of the war was conducted on the surface and at night, see Submarine warfare. This period, before the Allied forces developed truly effective antisubmarine warfare (ASW) tactics, was referred to by German submariners as "die glückliche Zeit" or the "happy time.
Later in the war, Germany developed an acoustic homing torpedo, the G7es. It was primarily designed to combat convoy escorts. The acoustic torpedo was designed to run straight to an arming distance of 400 meters and then turn toward the loudest noise detected. This sometimes ended up being the U-boat itself; at least two submarines may have been sunk by their own homing torpedoes. (Problems with steering mechanisms on normal torpedoes made them occasionally lethal to the firing boat as well). Additionally, it was found these torpedoes were only effective against ships moving at greater than . At any rate, the Allies countered acoustic torpedoes with noisemaker decoys such as Foxer, FXR, CAT and Fanfare.
U-boats also adopted "pattern-running" torpedoes which ran to a preset distance, then traveled in either a circular or ladder-like pattern. When fired at a convoy, this increased the probability of a hit if the weapon missed its primary target.
Throughout the war, an arms race evolved between the Allies and the Kriegsmarine, especially in detection and counter-detection. Sonar (ASDIC in Britain) allowed allied warships to detect submerged U-boats (and vice versa) beyond visual range but was not effective against a surfaced vessel; thus, early in the war, a U-boat at night or in bad weather was actually safer on the surface. Advancements in radar became particularly deadly for the U-boat crews, especially once aircraft-mounted units were developed. As a countermeasure, U-boats were fitted with radar warning receivers, to give them ample time to dive before the enemy closed in. U-boat radar was also developed, but many captains chose not to utilize it for fear of broadcasting their position to enemy patrols.
The Germans took the idea of the Schnorchel (snorkel) from captured Dutch submarines, though they did not begin to implement it on their own boats until rather late in the war. The Schnorchel was a retractable pipe which supplied air to the diesel engines while submerged at periscope depth, allowing the boats to cruise and recharge their batteries while maintaining a degree of stealth. It was far from a perfect solution, however. There were problems with the device's valve sticking shut or closing as it dunked in rough weather; since the system used the entire pressure hull as a buffer, the diesels would instantaneously suck huge volumes of air from the boat's compartments, and the crew often suffered painful ear injuries. Waste disposal was a problem when the U-boats spent extended periods without surfacing. Speed was limited to , lest the device snap from stress. The schnorchel also had the effect of making the boat essentially noisy and deaf in sonar terms. Finally, Allied radar eventually became sufficiently advanced such that the schnorchel head itself could be detected. The U-boats had a radar detector but the Allies changed to centimetric radar which the Germans did not discover.
The later U-boats were covered in a sound-absorbent rubber coating to make them less of a torpedo target. They also had the facility to release a chemical bubble-making decoy, known as Bold, after the mythical kobold.
The U-110, a Type IXB, was captured in 1941 by the Royal Navy, and its Enigma machine and documents were removed. Further code books were captured by raids on weather ships. The U-505, a Type IXC, was captured by the United States Navy in 1944. It is presently a museum ship in Chicago at the Museum of Science and Industry. The U-505 was captured along with the current codebooks, but there were fears that a security breach would alert the Germans to the capture of their codes.
The initial Type 201 was a failure because of hull cracking; the subsequent Type 205, first commissioned in 1967, was a success, and 12 were built for the German navy. To continue the U-Boat tradition and "brand name" the new boats received the classic U designation starting with the U-1.
With the Danish government's purchase of two Type 205 boats, the German government realised the potential for the submarine as an export. Three of the improved Type 206 boats were sold to the Israeli Navy becoming the Gal class. The German Type 209 diesel-electric submarine was the most popular export-sales submarine in the world from the late 1960s into the first years of the 21st century. With a larger 1000-1500 tonne displacement, the class was very customizable and has seen service with 14 navies with 51 examples being built as of 2006.
Germany has brought the U-Boat name into the 21st century with the new Type 212. The 212 features an air-independent propulsion system using hydrogen fuel cells. This system is safer than previous closed cycle diesel engines and steam turbines, cheaper than a nuclear reactor and quieter than both. While the Type 212 is also being purchased by Italy, the Type 214 has been designed as the follow-on export model and has been sold to Greece, South Korea and Turkey.
In July 2006, Germany commissioned its newest U-boat, the U-34, a Type 212.