List of ships sunk by submarines by death toll

While submarines were invented centuries ago, development of self-propelled torpedoes during the latter half of the 19th century dramatically increased the effectiveness of military submarines. Initial submarine scouting patrols against surface warships sank several cruisers during the first month of World War I. Incidental submarine encounters with merchant ships were performed by signalling ships to stop, then sinking them after evacuation of the crew, in accordance with international law.

Source: Wikipedia — List of ships sunk by submarines by death toll (CC BY-SA 4.0)