List of ships sunk by submarines by death toll

Self-propelled torpedoes dramatically increased effectiveness of submarine warships. Initial scouting patrols against surface warships sank several cruisers in the first month of World War I. Incidental encounters with merchant ships were handled by signalling the ship to stop and sinking the ship after removing the crew in accordance with international law. After unrestricted submarine warfare began in February 1915, any ship might unexpectedly sink rapidly from heavy underwater hull damage inflicted by torpedoes. Many large ships sank unknown to friendly forces, and the submarines which sank them were too small to rescue more than a few survivors. Heavy personnel casualties continued through World War II, and there have been a few later sinkings.