Recommissioned 25 September 1939, "Fox" was assigned to the Atlantic Squadron and from 25 October performed escort and patrol duty along the Atlantic coast and in the Caribbean area until August 1940. Arriving Balboa, Canal Zone, 25 August she performed inshore patrol duty from this port until sailing for San Francisco, California, 25 October. "Fox" patrolled with the Local Defense Forces, 12th Naval District until departure 2 January 1941 for Seattle, Washington. She patrolled off the coast of Washington and Oregon with Local Defense Forces, 13th Naval District, until December 1941, except while under overhaul from March to June, and while assigned to temporary duty in the 12th Naval District from 20 August to 9 October.