Unrestricted submarine warfare (February 1917)

U-Boat Campaign
Part of the Naval Theatre of World War I
A German postcard depicting the U-boat SM U-20 sinking RMS Lusitania
Date 28 July 1914 – 11 November 1918 (4 years, 3 months and 2 weeks) Location Atlantic Ocean, North Sea, Mediterranean Sea, Black Sea Result Allied Victory
Belligerents
Royal Navy  Royal Canadian Navy  French Navy  Regia Marina  United States Navy  Imperial Japanese Navy  Brazilian Navy  Imperial Russian Navy  Romanian Navy	Kaiserliche Marine  Austro-Hungarian Navy  Bulgarian Navy
Commanders and leaders
Lord Fisher Sir Henry Jackson Sir John Jellicoe Sir Rosslyn Wemyss	Hugo von Pohl Gustav Bachmann Henning von Holtzendorff Reinhard Scheer
Strength
? surface vessels 366 Q-ships	351 U-boats
Casualties and losses
5,000 merchant ships sunk 15,000 merchant sailors killed 104 warships sunk 42 warships damaged 61 Q-ships sunk	217 U-boats lost to all causes 5,000 sailors killed

The U-boat Campaign from 1914 to 1918 was the World War I naval campaign fought by German U-boats against the trade routes of the Allies. It took place largely in the seas around the British Isles and in the Mediterranean. The German Empire relied on imports for food and domestic food production (especially fertilizer) and the United Kingdom relied heavily on imports to feed its population, and both required raw materials to supply their war industry; the powers aimed, therefore, to blockade one another. The British had the Royal Navy which was superior in numbers and could operate on most of the world's oceans because of the British Empire, whereas the Imperial German Navy surface fleet was mainly restricted to the German Bight, and used commerce raiders and unrestricted submarine warfare to operate elsewhere.

In the course of events, German U-boats sank almost 5,000 ships with nearly 13 million gross register ton, losing 178 boats and about 5,000 men in combat.

In August 1914, a flotilla of nine U-boats sailed from their base in Heligoland to attack Royal Navy warships in the North Sea in the first submarine war patrol in history. Their aim was to sink capital ships of the British Grand Fleet, and so reduce the Grand Fleet's numerical superiority over the German High Seas Fleet. The first sortie was not a success. Only one attack was carried out, when U-15 fired a torpedo (which missed) at HMS Monarch. Two of the ten U-boats were lost.

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Wikipedia