Subs are sneaky; that's what they do. When subs sank vessels without warning...it angered people. But if a sub skipper (ship's captain) warned a ship before he sank it; he endangered himself, his vessel, and his men. Because while he's on the surface "being a nice guy", the allies are coming to sink him...because the ship he intends to sink has just radioed the allies of the subs POSITION!
American citizens died when German submarines sank European ships.
Because a German submarine was responsible for the sinking of the Luisitania, with many American citizens on board.
Germany's unrestricted submarine warfare
German u boats were attacking civilian ships. Many US trade ships, and civilian transport ships were attacked. when the USS lusitania sunk and 100 US citizens died, the US declared war on Germany becuz of Germany's unrestricted submarine warfare
The US revolutionary war
unrestricted submarine warfare
Un-restricted submarine warfare
Submarine Warfare
Germany's return to unrestricted submarine warfare.
submarine
submarine warfare
"Unrestricted submarine warfare" led to a u-boat sinking of a passenger ship, Lusitania, with US citizens on board. This was the official excuse to enter the war.