World War 1.
WWI; Guerre de Course-Merchant Raiding aka Commerce raiding.
arm the merchant ships
The tactic began in WWI and is known as Unrestricted Submarine Warfare.
Frederick C. Matthews has written: 'American merchant ships, 1850-1900' -- subject(s): History, Merchant marine, Merchant ships, Ships
Merchant ships did (and still do!) travel all over the world, wherever there are sea ports.
Roger Villar has written: 'Merchant ships at war' -- subject(s): Armed merchant ships, British Naval operations, Falkland Islands War, 1982, Merchant ships
103 merchant ships were sunk in world war one
Congress denied President Wilson the right to do what with merchant ships?
Orchard Cook has written: 'Mr. Cook's motion for arming merchant vessels' -- subject(s): Armed merchant ships, Merchant ships
Knarrs, which are Viking merchant ships.
It was a promise made in 1916 between Germany and the United States, before the US entered the war, allowing armed merchant ships, but not passenger ships, to be torpeoded without warning. However it was rescinded in 1917