The Germans torpedoed the U.S. Gulflight without warning despite America's neutrality. While the German government apologised, they would not alter their policy of unrestricted submarine warfare.
Editors. "U.S. vessel Gulflight sunk by German submarines". The Literary Encyclopedia. First published 01 March 2010; last revised 30 November -1.
[http://www.litencyc.com/php/stopics.php?rec=true&UID=12290, accessed 19 April 2015.]