sentences:  The United States entered World War I on 6 April 1917, and "Castine"s time in the Caribbean ended in July 1917.On 5 August, she sailed to join the Patrol Force at Gibraltar, where she served until 21 December 1918, when she returned to the United States.The Navy Cross was awarded to the son of Rear Admiral Peter C. Assersen, Captain William Christian Asserson (21 August 1875 – 8 July 1939), for distinguished service as commanding officer of "Castine" while engaged in the exacting and hazardous duty of transporting troops and supplies to European ports through waters infested with enemy submarines and naval mines during World War I.