Uboats

U-boats, a contraction of Unterseeboot, are submarines used by the German Navy. The term is most closely associated with German submarines operated during World War I and World War II, though modern German submarines also carry the designation. U-boats have been a central element of German naval strategy and naval warfare since the early 20th century.

In World War I, U-boats aimed to cut Allied supplies by enforcing a naval blockade. They practiced unrestricted submarine warfare, sinking merchant ships to pressure Britain and its allies. The campaign caused significant Allied losses and shaped public opinion, contributing to the United States entering the war. Allied countermeasures—such as convoy systems, improved depth charges, and anti-submarine warfare—gradually eroded U-boat effectiveness. After the war, the Treaty of Versailles restricted German submarine construction.

Germany rebuilt its submarine force in the 1930s, and U-boats again played a central role in the Battle of the Atlantic during World War II. The objective was to sever transatlantic supply lines and starve Britain into submission. Early successes gave way to heavy Allied countermeasures, including improved code breaking (the Ultra program), radar, more capable depth charges, and escort groups. The most common vessels were the Type VII and Type IX; late in the war, the Type XXI introduced enhanced underwater performance and snorkel capability.

Technically, U-boats relied on diesel-electric propulsion: diesel engines while surfaced to charge batteries, and electric motors when submerged. Armament typically included torpedoes and, on some early boats, a deck gun. Submarine warfare also benefited from intelligence advantages and countermeasures such as sonar, depth charges, and aerial patrols.

In the postwar era, Germany continued to develop submarines for the Bundesmarine, emphasizing diesel-electric designs and, later, models with air-independent propulsion. U-boats remain a defining element of submarine warfare and naval doctrine.