Bagley operated along the east coast and in Cuban waters during the first year following her commissioning. Assigned to Destroyer Division 7, Battle Force, in June 1938, she participated in fleet maneuvers in the Canal Zone, Haitian-Cuban Florida area, and later on the West Coast.
On 7 December 1941 Bagley was moored at Pearl Harbor and when the Japanese planes attacked, she opened fire immediately and assisted in the destruction of' several enemy airplanes. Between December 1941 and 30 May 1942, when she arrived in Brisbane, Australia, Bagley performed patrol and escort duties in the Central and Eastern Pacific, taking part in raids on Bougainville (20 February 1942) and Salamaua-Lae (10 March). Between 7 and 30 August 1942 she was at Guadalcanal and took part in the First Battle of Savo Island (9 August) splashing one plane. Following the battle she rescued approximately 450 survivors of Astoria (CA 34), Vincennes (CA-44), and Quincy (CA-39). (continued)