During the first year and a half of her commissioned service, Mahan's primary assignment was the testing and evaluation of her weapons systems, RUR-5 ASROC and RIM-2 Terriers.

For the next 6 months she cruised with other units of the 7th Fleet, taking part in antisubmarine, antiaircraft, and amphibious exercises as well as making good-will calls on ports in the Far East.

In addition to assignments in Japanese and Philippine waters, she spent (on this tour) a total of four weeks cruising off South Vietnam before returning to San Diego on 10 March 1964.

Remaining on the west coast until late 1965, she underwent a 5½ month overhaul, from 1 May 1965 to 20 October 1965, followed by test and training exercises and a demonstration of her antisubmarine warfare capabilities before members of the United States-Canadian Military Cooperation Committee on 9 December 1965.

Departing San Diego on 19 October, she sailed to Pearl Harbor for antisubmarine training operations and then continued on to the western Pacific, arriving at Subic Bay on 22 November 1965.

The period 1 December 1966 through 4 June 1967 again saw Mahan in the western Pacific where, as before, she operated off Vietnam, patrolling the Gulf of Tonkin (PIRAZ) station and providing gunfire support.

Arriving back at San Diego on 17 June, Mahan sailed on 31 July to represent the Navy at Seattle's annual Sea Fair.

Following a regular overhaul in Philadelphia from April 1980 to May 1981, Mahan was selected to install and test the Terrier New Threat Upgrade (NTU) Combat System with the improved RIM-67 Standard Missile Two Block II (Extended Range).

She also represented Commander Sixth Fleet, serving as official starter for the inaugural Monaco-New YorkYacht race, (hosting Monaco's Crown Prince and the Deputy Under-Secretary of the Navy).

Mahan also served as East Mediterranean Ready Ship off of Israel and Lebanon and was involved in the Gulf of Sidra Freedom of Navigation operations off the coast of Libya.

The crowning achievement of the cruise occurred in November 1989, when Mahan added another first to her long list of accomplishments by firing the first SM-2 Block II (ER) in Northern Europe.