U-boat
U-boats are naval submarines operated by Germany, especially during World War I and World War II. The term is an anglicized form of the German word U-Boot, a shortening of Unterseeboot. Austro-Hungarian Navy submarines were also known as U-boats.
U-boats are especially known for their use in unrestricted submarine warfare in both world wars, attempting 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 February 1917 the Germans, facing deadlock on the continent, saw no other option than to resume the campaign. 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, 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.
Early U-boats (1850–1914)
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 U-boats from Russia, did Tirpitz order one submarine. The 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 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 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.
In March 1907, the Germaniawerft received an order from the Austro-Hungarian Navy for two U-boats and in October Norway ordered a similar U-boat.
These foreign U-boats were based on an improved U-1 design. Between 1908 and 1910, the German navy ordered fourteen boats with four 45 cm torpedo tubes and two reload torpedoes. These boats used a kerosene engine which was safer than gasoline and more powerful than steam, but the white exhaust of the kerosene betrayed the presence of the U-boats, robbing them of their primary asset, their stealth. Diesel engines did not have that disadvantage, but a powerful and reliable diesel engine was still under development. As some equipment could not be delivered within the specified weight limits, there was some variation in the total weight of each U-boat. Usually this was solved by reducing the number of battery cells, which affected underwater performance. The last two of these U-boats, the Type U 17, was designed to receive diesel engines but due to delays in developing a lightweight diesel engine, these U-boats were equipped with kerosene engines.
Between 1910 and 1912, twenty-three diesel U-boats were ordered when diesel engines finally became available: four Type U 19 U-boats on 20 November 1910 from KWD with MAN engines and four similar Type U 23 U-boats from Germaniawerft with Germaniawerft engines on 18 March 1911. These boats were larger to accommodate the diesel engines, and were equipped with torpedo tubes. On 12 February 1912 a further four similar Type U 27 were ordered from KWD, and although Germaniawerft experienced problems with its diesel engines, it received an order for eleven Type U 31 U-boats. Due to these problems, delivery of these U-boats was delayed up to eight months and ran into 1915.
At the start of World War I in 1914, Germany had 48 submarines of 13 classes in service or under construction.
Pre World War I Classes
World War I (1914–1918)
Operations
During 1914, the U-boats operated against the British fleet: on 5 September 1914, the light cruiser was sunk by, the first ship to be sunk by a submarine using a self-propelled torpedo. On 22 September, sank the armoured cruisers,, and. As a result, the British Grand Fleet had to withdraw to safer waters in Northern Ireland. Against merchant ships, U-boats observed the "prize rules" which meant they had to stop and inspect the ship, and take the crew off the ship before they could sink it. On 20 October 1914, sank the first merchant ship,, off Norway. Only ten merchants were sunk in that way before policy was changed on 18 February 1915.| Surface warships | |
| Mines | |
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| Q-ships | |
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| Unknown | |
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On the continent German hopes for a quick victory were dashed and a stalemate had settled on the front. The Germans hoped to break the deadlock by starting an unrestricted submarine campaign against shipping in the waters around the British Isles. This was also cited as a retaliation for British minefields and shipping blockades. Under the instructions given to U-boat captains, they could sink merchant ships, even neutral ones, without warning. Only 29 U-boats were available for the campaign, and not more than seven were active around the British Isles at any time. The U-boats failed to enforce a blockade but the sinking of three liners including the RMS Lusitania, with loss of American lives, outraged the US so that the Kaiser had to stop the campaign on 19 September 1915. After the stop of the campaign, most of the U-boats were sent to the Mediterranean.
At the beginning of 1916, 54 U-boats were available, and the Kaiser allowed again operations around the British Isles, but with strict rules: no attacks on liners, and outside the war zone around the British Isles attacks were only allowed on armed merchant ships. But on 24 March, after 25 Americans were killed in the torpedoing of the ferry the US threatened to sever diplomatic ties, which persuaded the Germans to fully reapply prize rules.
In September 1916, 120 U-boats were in service, and again some were sent to the Mediterranean. Whilst around British Isles prize rules were observed, in the Mediterranean a new unrestricted campaign was started. The renewed German campaign was effective, sinking of shipping between October 1916 and January 1917. Despite this, the deadlock situation on the continent frontlines demanded even greater results, and on 1 February 1917, Germany restarted the unrestricted submarine campaign around British Isles. Germany took the gamble that the U-boat campaign would force the UK out of the war before the US could effectively enter. On 3 February, the US severed diplomatic relations with Germany, and on 6 April, the US declared war on Germany. Unrestricted submarine warfare in 1917 was very successful, sinking more than a month. With the introduction of convoys in August 1917, shipping losses declined to a month on average, which was not sufficient to force the UK out of the war. With deteriorating conditions on the continent, all U-boats were recalled on 31 October 1918. Under the terms of armistice of 11 November 1918, U-boats were to immediately surrender. All U-boats were either scrapped or given to Allied navies.
Of the 373 German U-boats that had been built, 179 were operational or nearly operational at the end of the war. 178 were lost by enemy action. 512 officers and 4894 enlisted men were killed. Of the surviving German submarines, 14 U-boats were scuttled and 122 surrendered. They sank 10 pre-dreadnought battleships, 18 cruisers, and several smaller naval vessels. They further destroyed 5,708 merchant and fishing vessels for a total of and the loss of about 15,000 sailors. The Pour le Mérite, the highest decoration for gallantry for officers, was awarded to 29 U-boat commanders. The three most successful U-boat commanders were Lothar von Arnauld de la Perière, followed by Walter Forstmann, and Max Valentiner.
World War I Classes
When the German Army captured three ports on the Belgian coast in the opening stages of the war, the German navy ordered coastal submarines to be operated from these ports against the English coast. As the war was then expected to end in a matter of months, only very small U-boats could be designed with an expected building time of four months. On 15 October 1914 fifteen Type UB I U-boats were ordered, and based on that design, on 23 November a further fifteen Type UC I coastal minelaying U-boats were ordered. Given the weakness of the Austro-Hungarian Navy and the need to help their Turkish Allies, the German Navy sent some of these U-boats to the Dardanelles and Black Sea.In the spring of 1915 it became clear that the war would continue well into 1916 and more coastal U-boats were ordered. The Type UB I and UC I had fullfilled the expectations but were underpowered. Thirty U-boats of the successing Type UB II were ordered, which were with around double in size. As with the cessation of unrestricted U-boat warfare in September 1915, mine warfare became more prominent, a record number of 64 Type UC II minelaying U-boats were ordered, which allowed for the first time for the mass-production of a U-boat. The Type UC II proved to be an ideal combination of mine and torpedo armament: on the same patrol it could lay minefields and attack shipping on the way to its target.
On the resumption of the U-boat campaign in 1916, it was realized that not enough large U-boats could be built in time, and as a compromise it was decided to build an enlargened coastal U-boat capable of patrolling in the Western Approaches. The hull of the Type UC II was taken as a basis, the forward mineshaft room was replaced with a torpedo room, more powerful diesel engines provided better surface speed and larger fuel tanks extended the range. On 2 May 1916 the first twenty-four Type UB III were ordered and as the war prolonged, more than 200 were ordered but only 96 were commissioned before the armistice.
| standard U-boat types | Type U 51, Type U 57, Type U 63, Type U 66, Type U 81, Type U 87, Type U 93 |
| U-cruisers and merchant U-boat types | Type U 139, Type U 142, Type U 151, Type UD 1 |
| UB coastal U-boat types | Type UB I, Type UB II, Type UB III, Type UF, Type UG |
| UC coastal minelaying U-boat types | Type UC I, Type UC II, Type UC III |
| UE ocean minelaying U-boat types | Type UE I, Type UE II |