USS Ericsson (DD-56) becomes the first US warship to fire a torpedo at a U-boat during the First World War, in an attempt to drive off a U-boat that was attacking two sailing vessels.
How to cite this article: Rickard, J (28 December 2007), 21 May 1917, http://www.historyofwar.org/firstworldwar/daybyday/1917_05_21.html