A submarine sunk the liner 'Lusitania'. Many Americans died. USA was horrified, declared war on Germany.
Sinking civilian ships without warning (un-restricted submarine warfare).
Germany's submarine warfare was unrestricted. These attacks led to World War I.
unrestricted submarine warfare
Germany's unrestricted submarine warfare
unrestricted submarine warfare
Submarine Warfare
German submarine warfare
unrestricted submarine warfare
Germany's unrestricted submarine warfare
WW1 introduced submarine warfare, tanks, chemical warfare, and aerial combat. Man's history already knew battleship warfare from Tsushima in 1905; and massed land warfare consisting of infantry. WW2 REFINED submarine warfare, tanks, and aerial warfare; chemical warfare was outlawed by treaty.
1. Unrestricted Submarine Warfare 2. Sinking of several US ships
the Germans' use of unrestricted submarine warfare