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Commissioned on 14 December 1906, U-1 was the first in a long line of German U-boats (the name is a shortening of Unterseeboot, or ‘under-sea boat’). She was more of a trials vessel than an operational warship, but she successfully completed arduous endurance tests, including a voyage of 1,088 kilometres (587 nautical miles) between the German ports of Wilhelmshaven to Kiel in bad weather. U-1 formed the basis for the development of a series of seven larger and increasingly sophisticated submarines with heavier armament.
Initially, there was no consensus on how long a U-boat crew could reasonably be expected to stay at sea in such cramped conditions. Following U-1’s achievement, the whole flotilla was deployed in the North Sea during the winter of 1912/13. They were sent to form a patrol line 483 kilometres (300 miles) from harbour, equivalent to the distance from the German island of Heligoland to English coastal waters, and were ordered to stay on station for as long as possible. To the surprise of many officers, who had predicted that crews could manage no more than three days at sea, the U-boats stayed out for 11 days. Improvements in the stowage of supplies and general habitability allowed this to be significantly extended, and, by the end of the First World War, the large ‘U-cruisers’ were routinely attacking Allied shipping off the east coast of the USA.
Image: Wikimedia Commons
Despite their potential, U-boats were neglected by most senior German naval officers during the pre-war period – Grand Admiral Alfred von Tirpitz had actively opposed the introduction of submarines as an unwarranted diversion of resources from the battleships that he believed to be the key element of naval power. A number of more open-minded officers disagreed, ensuring that U-boats were included in the High Seas Fleet exercises in 1913. However, as late as 1914, there were only 33 U-boats in service, with a further 28 under construction – a stark contrast to the Royal Navy’s 74 submarines in commission, with 31 more being built (see also MHM 108, September 2019).
In an infamous incident within weeks of the outbreak of war, U-9 sank a squadron of three old British armoured cruisers, Aboukir, Cressy, and Hogue, in little more than an hour on 22 September 1914. This highlighted the vulnerability of British merchant shipping – a weakness that Germany exploited between February and September 1915 with an ‘unrestricted’ U-boat campaign in which Allied and neutral merchant vessels were sunk without warning, in defiance of international law. Initially, only 21 U-boats were available – but this small force still managed to sink 750,000 tons of Allied shipping, before the campaign was abandoned due to intense US diplomatic pressure in the aftermath of U-20’s sinking of the Cunard liner Lusitania, in which 128 American citizens died.
After the Battle of Jutland in mid-1916, it became clear that the battleships of the Kaiser’s High Seas Fleet would be unable to break the Royal Navy’s blockade, which was slowly strangling the German war economy. The outcome of the war’s largest naval battle was neatly summed up in an American press report: ‘The German Fleet has assaulted its jailor, but it is still in jail.’
Despite the propaganda, which attempted to portray Jutland as a crushing German victory, senior officers including the fleet commander, Admiral Reinhard Scheer, recognised the truth. In a confidential report to the Kaiser made only six weeks after the battle, Scheer wrote:
A victorious end to the war within a reasonable time can only be achieved through the defeat of the British economic life — that is, by using the U-boats against British trade… It is my duty to advise Your Majesty that, in British waters, where American interests are strong, it will be impossible to avoid incidents, however conscientious our commanding officers may be.
The renewed unrestricted campaign that began in February 1917 was a far more serious affair. U-boat strength had risen to a total of 111 vessels, which sank 2,988,031 tons of Allied merchant shipping in their first five months of operations. Such losses were devastating: at one point, the total British reserves of wheat were reduced to six weeks’ supply. The situation rapidly became critical, prompting The Times’ influential war correspondent Lieutenant-Colonel Repington to wonder whether the army could win the war before the navy lost it.
By 1917, a wide variety of U-boats were in service, ranging from small coastal types to large ‘U-cruisers’. Arguably the most cost-effective were the UB coastal-patrol submarines and the UC coastal minelayers that equipped the Flanders flotilla, formed in March 1915 at the inland port of Bruges in occupied Belgium. Commanded by Kapitänleutnant Bartenbach, the force initially comprised nine UB- and seven UC-type U-boats, which proved to be ideal for operations in the confined waters of the Channel and the North Sea. The boats used Zeebrugge and Ostend as exit ports, and became such a menace that Field Marshal Douglas Haig’s planning for the Third Ypres offensive included an amphibious assault (codenamed Operation Hush) to capture their bases. (While the offensive never made enough progress to allow this operation to be launched, large-scale raids were made in 1918 on Zeebrugge and Ostend, with the aim of blocking their harbours.)
The belated introduction in April 1917 of a new system of convoys, whereby merchant ships would travel in groups with a naval escort, proved to be the key factor in countering the U-boat menace. Although a total of 6,000,000 tons of Allied shipping was lost in 1917, monthly losses in 1918 were reduced to a sustainable 300,000 tons and 69 German submarines were sunk during the year. Despite increasing odds, the U-boat arm’s morale remained high even at the end of the war, in marked contrast to the high incidence of indiscipline and outright mutiny in the surface fleet.
U-boat minelayers
The UC boats were the world’s first operational minelaying submarines, and during 1915 laid a total of 648 mines between Grimsby and the Dover Strait. In 1916, U-75 – one of the larger UE minelayers – inflicted one of the most famous casualties of the war when one of her mines sank the armoured cruiser HMS Hampshire with the loss of 737 men, including Lord Kitchener, the Secretary of State for War.
As the war progressed, mine warfare tactics became increasingly sophisticated. U-boats laid more than 400 mines off the south coast of Ireland in 1917. At least 330 of these were cleared by a force of minesweepers working out of Queenstown (now Cobh), but it soon became apparent that the swept mines were being replaced within a matter of days. The commander of the minesweeper flotilla saw this as an opportunity, and on 4 August he ordered his vessels to go through the motions of mine clearing, but not to deploy their sweeps so that the mines were left in place. This was done, and that evening UC-44 moved in to renew the field, which her crew believed they had seen being swept. At about 22.30 hours, the town of Waterford was awoken by a shattering explosion as the boat struck one of the mines laid by UC-42 a few days earlier. UC-44’s captain, Kurt Tebbenjohanns, was rescued, complaining loudly to his captors about the inefficiency of British minesweeping.
By 1918, the ocean-going UE-II minelaying U-boats were entering service. A total of ten were completed, each carrying 42 mines launched through stern chutes, plus four 50cm (19.7in) torpedo tubes. One of these, U-117, mined the approaches to the US naval bases at Norfolk and Newport News in Virginia. Her mines badly damaged the pre-dreadnought battleship USS Minnesota and sank 23 other Allied vessels.
Torpedoes and guns
Within days of the outbreak of war, it became clear that U-boats had to be cautious when operating in areas patrolled by Allied warships – on 9 August 1914, the light cruiser HMS Birmingham rammed and sank U-15 after catching it surfaced in the North Sea. German captains rapidly adopted submerged attacks against warships – but, while less risky, even these could go disastrously wrong: the first great U-boat ace Otto Weddigen was killed with his entire crew on 18 March 1915 after an abortive attack on HMS Neptune in the Pentland Firth. (U-29 lost trim after firing her torpedoes, broke surface, and was rammed and sunk by HMS Dreadnought, which thus became the only battleship ever to sink a submarine.)
However, it was soon found that it was far more effective for craft to surface and use their deck guns against unescorted merchant vessels in order to conserve torpedoes. The prime exponent of this tactic was the most successful U-boat commander of all time, Lothar von Arnauld de la Perière, who sank 194 ships (totalling 454,000 tons) using his 88mm deck gun and just four torpedoes.
U-boat experiments, 1914-1918
Germany was the first nation to experiment with submarine aircraft carriers, initiated by the Imperial German Naval Air Service commander Oberleutnant zur See Friedrich von Arnauld de la Perière (the younger brother of Lothar), who commanded a flight of two Friedrichshafen FF.29 reconnaissance seaplanes in Zeebrugge. In December 1914, one of the unarmed FF.29s was modified to carry a few 12kg (26.5lb) bombs and bombed Dover, although it was apparent that the type suffered from a lack of range.
Arnauld discussed the problem with Kapitänleutnant Walther Forstmann, the commander of U-12, and came up with a plan to use the boat to carry a single FF.29 to a launch point just off the English coast, before partially submerging to allow the seaplane to float clear and take off. On 15 January 1915, U-12 left Zeebrugge with an FF-29, armed with a single bomb, on its deck. As soon as the submarine reached the open sea, heavy swells threatened to damage the aircraft, and Forstmann ordered the immediate launch of the seaplane. The U-boat’s forward tanks were flooded and the seaplane floated off the deck and took off. Arnauld flew along the English coast and returned safely to Zeebrugge.
This qualified success inspired Arnauld and Forstmann to propose further experiments to the German Naval Command, but these were vetoed as the concept was considered to be impractical. The idea was re-examined in 1917, as it was felt that future classes of long-range U-cruisers would benefit from carrying small scouting seaplanes. Two aircraft were designed to meet this requirement – the biplane Hansa-Brandenburg W.20 and a low-wing monoplane, the Luftfahrzeug-Gesellschaft L.F.G. Stralsund V.19. Prototypes of both designs were built, but none of the U-cruisers intended to carry them were completed by the end of the war.
The Kaiserliche Marine’s experience of submarine operations profoundly influenced the doctrine of the later Kriegsmarine, the navy of Nazi Germany from 1935 to 1945: in May 1918, an experimental ‘wolf-pack’ of six U-boats was formed which intercepted several convoys and sank three merchant vessels for the loss of two U-boats. The trial was not repeated, as the technology of 1918 was inadequate for the effective command and control of such forces – but the idea’s potential impressed the future Grand Admiral Karl Dönitz, who was then a junior officer commanding UC-25.
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