Uboat

U-boat is the English designation for German submarines, derived from Unterseeboot, meaning undersea boat. The term was used most prominently for submarines operated by the German Navy during World War I (Kaiserliche Marine) and World War II (Kriegsmarine). U-boats were central to Germany's naval strategy, aiming to interdict Allied and merchant shipping and force Britain to surrender or negotiate.

In World War I, U-boats pursued unrestricted submarine warfare to choke Allied supply lines. Notable actions included U-9’s 1914 victory sinking three British cruisers—HMS Aboukir, HMS Hogue, and HMS Cressy—and the later sinking of passenger liner Lusitania in 1915. The U-boat campaign influenced Allied strategy and American policy, contributing to entry into the war.

In the interwar period, Germany evaded strict limitations, and after 1935 rebuilt its U-boat arm. In World War II, the U-boat fleet sought to blockade Britain in the Battle of the Atlantic, employing Type VII and Type IX submarines as the workhorses. U-boat operations were aided by wolfpacks and long-range patrols.

Advances in electronics, propulsion, and sensors improved performance, but Allied countermeasures—convoys, escort vessels, long-range aircraft, radar, sonar, and the Ultra program that decoded Enigma traffic—eroded U-boat effectiveness. The snorkel allowed submerged running at periscope depth while running diesel, extending endurance but still vulnerable.

After the war, many U-boats were scuttled; remaining craft were surrendered or scrapped. The term U-boat remains synonymous with German submarine warfare and is used in historical and popular contexts to describe submarine operations in both world wars.