Atlantic U-boat campaign of World War I

The Atlantic U-boat campaign of World War I (sometimes called the "First Battle of the Atlantic", in reference to the World War II campaign of that name) was the prolonged naval conflict between German submarines and the Allied navies in Atlantic waters –the North Sea, the seas around the British Isles, and the coast of France.

Initially the U-boat campaign was directed against the warships of the British Grand Fleet, which were, along with other Entente powers, enforcing the Naval Blockade of Germany. When the blockade extended to merchant ships and foodstuffs, U-boat fleet action was likewise extended to include action against the trade routes of the Allied powers. To counter the German submarines, the Allies moved shipping into convoys guarded by destroyers, blockades such as the Dover Barrage and minefields such as the North Sea Mine Barrage were laid, naval vessels disguised as merchant ships were constructed, indicator loops were strung across lengths of the North Sea, and aircraft patrols monitored the U-boat bases. Increased ship construction meant the amount of Allied shipping available remained fairly stable.

The U-boat campaign was not able to cut off supplies before the US entered the war in 1917, and in late 1918 the U-boat bases were abandoned in the face of the Allied advance.