On 6 March 1939, "Simpson" transited the Panama Canal to the Atlantic, and between 5 June and 30 August 1939, she carried out three training cruises for Naval Academy midshipmen. She then commenced training cruises for Naval Reservists, but at the outbreak of war in Europe, she was assigned Neutrality Patrol duty and sailed for the Caribbean on 6 September. There she carried out patrols and participated in exercises, including a fleet landing exercise at Culebra from 14 February to 10 March 1940. After one training cruise for midshipmen and one for reservists during the summer, she resumed Neutrality Patrol duties in the Caribbean in October.