What does the German naval term “U-boat” literally mean?

The German naval term “U-boat” literally means Unterseeboot, or “undersea boat.” The shortened English form comes from the German designation U-Boot, with the letter U standing for Untersee, meaning “undersea.”

The term was used for German submarines in both world wars, although German submarines also carried individual designations such as U-47 and U-boat classes such as Type VII. In English-language writing, “U-boat” usually refers specifically to a German submarine, especially one used during the First or Second World War.

A common mix-up is treating “U-boat” as a generic word for every submarine. Other navies used different systems, including the Royal Navy’s HMS designations and the U.S. Navy’s USS names. The word is best understood as a German naval term that became widely adopted in English because of Germany’s extensive submarine campaigns.

German U-boats attacked military and merchant shipping, making submarine warfare a major feature of both world wars.