When the United States declared war on Germany on 6 April 1917 entering World War I, the destroyer was anchored in the York River near Yorktown, Virginia. She had been there guarding the river mouth since February when American relations with Germany began to deteriorate as a result of the latter country's return to unrestricted submarine warfare. Soon after US Congress declared war, "Winslow" moved north to the New York Navy Yard to prepare for duty overseas. Less than a month later, she moved to Boston from where she got underway for Europe on 7 May with "Cassin", "Ericsson", , , and . After a 10-day passage, "Winslow" reported for duty at Queenstown, Ireland, on the 17th. On the 21st, she began patrolling the approaches to the British Isles.