Unrestricted submarine warfare is a type of naval warfare in which submarines sink merchant ships such as freighters and tankers without warning. The use of unrestricted submarine warfare has had significant impacts on international relations in regards to both the First World War and the Second World War. Its history has been dominated by German decision making.
German U-boat U-14 (early 1910s)
German art of the sinking of the Linda Blanche on 30 January 1915 by SM U-21. Passengers and crew are being allowed to disembark into lifeboats, as per cruiser rules.
American cartoon by Oscar Cesare showing the sinking of the Lusitania. Sinkings of passenger vessels without warning incensed neutral opinion.
Allied submarines were used extensively during the Pacific War and were a key contributor to the defeat of the Empire of Japan.
Japanese freighter Nittsu Maru sinks after being torpedoed by USS Wahoo on 21 March 1943.
Torpedoed Japanese destroyer Yamakaze photographed through the periscope of American submarine USS Nautilus on 25 June 1942.
Photograph of Makin Island taken from USS Nautilus during the raid on the island in August 1942.