Nickname of German submarines during ww1?

The nickname of German submarines during World War I was "U-boats," which stands for "Unterseeboot," meaning "undersea boat" in German. These submarines played a significant role in naval warfare, employing tactics such as unrestricted submarine warfare to disrupt Allied shipping. U-boats became notorious for their effectiveness in sinking merchant and military vessels. The term has since become synonymous with German submarines in both World Wars.