Naval mine ship, HMHS "Britannic", which was the sister ship of the RMS "Titanic." During World War II, the U-boat fleet, which dominated much of the battle of the Atlantic, was small at the beginning of the war and much of the early action by German forces involved mining convoy routes and ports around Britain. German submarines also operated in the Mediterranean Sea, in the Caribbean Sea, and along the U.S. coast. Initially, contact mines (requiring a ship to physically strike a mine to detonate it) were employed, usually tethered at the end of a cable just below the surface of the
Ocean liner the risk of being torpedoed by enemy submarines. The war was marked by the loss of many liners."Britannic", while serving as a hospital ship, sank in the Aegean Sea in 1916 after she struck a mine. Numerous incidents of torpedoing took place and large numbers of ships sank. "Kaiser Wilhelm der Grosse" was defeated and scuttled after a fierce battle with HMS "Highflyer" off the coast of west Africa, while her sister ship "Kronprinz Wilhelm" served as a commerce raider. The torpedoing and sinking of on 7 May 1915 caused the loss of 128 American lives at a time when