U-boat campaign

BelligerentsRoyal Navy
Royal Canadian Navy
French Navy
Regia Marina
United States Navy
Imperial Japanese Navy
Brazilian Navy
Imperial Russian Navy
Royal Romanian NavyImperial German Navy
Austro-Hungarian Navy
Bulgarian NavyCommanders and leadersLord Fisher
Sir Henry Jackson
Sir John Jellicoe
Sir Rosslyn WemyssHugo von Pohl
Gustav Bachmann
Henning von Holtzendorff
Reinhard ScheerStrength ~500 Royal Navy destroyers
~250 US destroyers
Various armed trawlers and smaller vessels
Defensively armed merchant ships
366 Q-ships 351 U-boatsCasualties 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
6,000 sailors killed

The U-boat campaign from 1914 to 1918 was the World War Inaval campaign fought by German U-boats against the trade routes of the Allies, largely in the seas around the British Isles and in the , as part of a mutual blockade between the German Empire and the United Kingdom.

Both Germany and Britain relied on food and fertilizer imports to feed their populations, and raw materials to supply their war industry. The British Royal Navy 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 submarine warfare to operate elsewhere.

German U-boats sank almost 5,000 ships with over 12 million gross register tonnage, losing 178 boats and about 5,000 men in combat. The Allies were able to keep a fairly constant tonnage of shipping available, due to a combination of ship construction and countermeasures, particularly the introduction of convoys.