U-boats were naval submarines operated by Germany, particularly in the First and Second World Wars. The term is an anglicised version of the German word U-Boot, a shortening of Unterseeboot, though the German term refers to any submarine. Austro-Hungarian Navy submarines were also known as U-boats.

The wolfpack was a convoy attack tactic employed in the Second World War. It was used principally by the U-boats of the Kriegsmarine during the Battle of the Atlantic, and by the submarines of the United States Navy in the Pacific War. The idea of a co-ordinated submarine attack on convoys had been proposed during the First World War but had no success. In the Atlantic during the Second World War the Germans had considerable successes with their wolfpack attacks but were ultimately defeated by the Allies. In the Pacific, the American submarine force was able to devastate Japan’s merchant marine, though this was not solely due to the wolfpack tactic. Wolfpacks fell out of use during the Cold War as the role of the submarine changed and as convoys became rare.