Combining initial training operations with a good will tour, Mahan departed New York 16 November 1936 for a two-month cruise to Caribbean and South American ports. She returned in January 1937 and operated along the east coast until July, when she sailed for the Pacific. Arriving on the west coast in mid August, she participated in fleet training operations off the southern California coast before proceeding to her new station at Pearl Harbor. Until December 1941, periodic visits to the west coast and a cruise to the Caribbean for fleet problems in February 1939 varied a busy schedule of training exercises and patrols in Hawaiian waters.
On patrol 7 December 1941, Mahan, with TF 12, was ordered to set course for the Japanese forces, thought to be headed for Jaluit from a position 200 miles south of Pearl Harbor, and “intercept and destroy.” Unable to locate the enemy, Mahan returned to Pearl Harbor on the 12th.
In late December, she carried reinforcements to the marine detachment at Johnston Island and evacuated the civilians to Hawaii. Mahan then conducted screening activities for inter-island and transoceanic convoys until 24 February, when she was assigned to a patrol station off Canton Island. Departing Canton Island 24 March, she returned to Hawaii thence proceeded to the west coast for overhaul. She next conducted patrols in Hawaiian and west coast waters until departing for the South Pacific 16 October 1942. En route on the 22d, with Lamson, she conducted a raid on Japanese patrol boats south of the Gilbert Islands, sinking two. Steaming with TF 61 north of the Santa Cruz Islands by the 27th, she was attacked by Japanese aircraft and splashed four. That same day, following her fine performance in the Battle of the Santa Cruz Islands, Mahan collided with South Dakota. Damage to both ships was severe. Following temporary repairs at Nouméa, New Caledonia, Mahan proceeded to Pearl Harbor where she was quickly given a new bow.
Mahan returned to the South Pacific 9 January 1943 and escorted convoys between the New Hebrides, New Caledonia and the Fiji Islands before establishing a patrol off New Caledonia in March. Resuming escort duties in April, she made one trip to Guadalcanal and back and then commenced operations in Australian waters. Moving to New Guinea, she began basing at Milne Bay 2 July. Continuously in action for the next 3 months, she participated in the landings at Nassau Bay 9 August, the bombardment of Finschhafen on the 22d and 23d, the preparations and covering force actions for the landings at Lae on 4 to 8 September and the landing of Australian troops at Finschhafen on the 22d, when her well-served guns splashed three enemy planes.
Through October and November, she operated out of Buna, patrolling around New Guinea. In December, Mahan bombarded Japanese installations in New Britain and on the 26th provided effective fire support for the landings at Cape Gloucester on that island. Shore bombardment of Gali, New Guinea, a short stay in Sydney, Australia and escort duties between New Guinea and New Britain followed. On 28 February 1944, before commencing convoy activities in the Admiralties, she turned her guns on Los Negros Island.
After more than two busy years in the war zone, in the spring of 1944 the veteran destroyer proceeded to San Francisco for overhaul. Early in July, she returned to Pearl Harbor and participated in exercises there until 15 August. Steaming via Eniwetok, Jaluit, Guam, Saipan and Ulithi, Mahan returned to New Guinea 20 October. She then escorted convoys between Hollandia and Leyte until taking up antisubmarine patrol duties off Leyte at the end of November.
On 7 December, while patrolling between Leyte and Ponson Island, the destroyer was attacked by a swarm of Japanese aircraft. In the ensuing engagement, she shot down three of the attacking planes but three of the remainder crashed into her. The resultant fires soon spread out of control to the ship’s magazines. The ship was abandoned and the survivors picked up by nearby vessels. An hour later Walke sank Mahan by gunfire and torpedoes.
Mahan received five battle stars for World War II service.