Editing U-boat (section)

=== Operations ===
{{main|U-boat campaign}}
[[File:THE IMPERIAL GERMAN NAVY'S FLANDERS FLOTILLA DURING THE FIRST WORLD WAR Q20345.jpg|thumb|upright|Sea mines are loaded in a UC coastal submarine in the harbour of Zeebrugge]]
During 1914, the U-boats operated against the British fleet: on 5 September 1914, the [[light cruiser]] {{HMS|Pathfinder|1904|6}} was sunk by {{SMU|U-21|Germany|6}}, the first ship to have been sunk by a submarine using a self-propelled torpedo. On [[Action of 22 September 1914|22 September]], {{SMU|U-9||2}} sank the [[Armored cruiser|armoured cruisers]] {{HMS|Aboukir|1900|6}}, {{HMS|Cressy|1899|6}}, and {{HMS|Hogue|1900|6}}. As a result, the British [[Grand Fleet]] had to withdraw to safer waters in Northern Ireland. Against merchant ships, U-boats observed the [[Rules of Prize Warfare|"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, {{SMU|U-17|Germany|6}} sank the first merchant ship, {{SS|Glitra}}, off Norway. Only ten merchants were sunk in that way before policy was changed on 18 February 1915. 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 [[blockade]]s. Under the instructions given to U-boat captains, they could sink merchant ships, even neutral ones, without warning.{{Sfn|Blair||pp=9-11}}

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 three sinkings of liners, with loss of American lives, outraged the US so that the [[Kaiser]] had to stop the campaign in September 1915: on 7 May 1915 {{SMU|U-20|Germany|6}} sank [[Sinking of the RMS Lusitania|RMS ''Lusitania'']]; on 19 August {{SMU|U-24||6}} sank {{SS|Arabic|1902|6}}; and on 9 September ''SM U-20'' sank [[RMS Hesperian|RMS ''Hesperian'']]. 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, 25 Americans were killed in the torpedoing of the ferry {{SS|Sussex}}, which was mistaken for a troopship by {{SMU|UB-29}}. 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 1.4&nbsp;million tons 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 [[United States declaration of war on Germany (1917)|US declared war on Germany]].{{Sfn|Blair||pp=10-13}}

{| class="wikitable floatright" style="text-align:left"
|+ German U-boat losses by cause
|-
|Surface warships
|{{right|55}}
|-
|Mines
|{{right|48}}
|-
|Submarines
|{{right|18}}
|-
|[[Q-ships]]
|{{right|11}}
|-
|Merchant ships
|{{right|7}}
|-
|Aircraft
|{{right|1}}
|-
|Accidents
|{{right|19}}
|-
|Unknown
|{{right|19}}
|-
|'''Total'''
|{{right|'''178'''}}
|}

Unrestricted submarine warfare in 1917 was very successful, sinking more than 500,000 tons a month. With the introduction of convoys in August 1917, shipping losses declined to 300,000 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.{{Sfn|Blair||pp=13-19}} An armistice became effective on 11 November 1918. Under the terms of armistice, all U-boats were to immediately surrender. Those in home waters sailed to the British submarine base at [[Harwich]], after which the vessels were studied, then scrapped or given to Allied navies.{{Sfn|King-Hall||pp=229-242}}

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.{{Sfn|Blair||p=18}} 512 officers and 4894 enlisted men were killed. Of the surviving German submarines, 14 U-boats were [[Scuttling|scuttled]] and 122 surrendered. They sank 10 [[pre-dreadnought battleship]]s, 18 heavy and light cruisers, and several smaller naval vessels. They further destroyed 5,708 merchant and fishing vessels for a total of 11,108,865 tons and the loss of about 15,000 sailors.{{Sfn|Clodfelter||p=428}}

The [[Pour le Mérite]], the highest decoration for gallantry for officers, was awarded to 29 U-boat commanders.{{Sfn|UBoatNet WWI Aces||}} Twelve U-boat crewmen were decorated with the [[Military Merit Cross (Prussia)|Goldenes Militär-Verdienst-Kreuz]], the highest bravery award for noncommissioned officers and enlisted men.{{Sfn|Fischer||p=16}} The most successful U-boat commanders of World War I were [[Lothar von Arnauld de la Perière]] (195 ships with 44,869 tons), followed by [[Walter Forstmann]] (149 ships with 391,607 tons), and [[Max Valentiner]] (144 ships with 299,482 tons).{{Sfn|Wragg|2014|p=51}}