When the United States entered World War I on 6 April 1917, Senior Captain Reynolds was commanding the Coast Guard's southern division at San Francisco. He was directed to report to the Commander, Twelfth Naval District for assignment where he was put in charge of harbor patrols for the district but also retained his old assignment. On 11 September 1917, he was reassigned as the district chief of staff, in addition to his former assignments. He remained as district chief of staff for the remainder of the war.