O'Bannon was the US Navy's most decorated destroyer during World War II, earning 17 battle stars and a Presidential Unit Citation.

[1] O'Bannon briefly trained for war in the Caribbean and sailed from Boston on 29 August 1942 for the Southwest Pacific, where the long and arduous Guadalcanal campaign had just begun.

For over a year, the Navy—stretched thin to cover its worldwide commitments at a period when new ships were just beginning to join the fleet in any number—was to fight and fight again in the Solomon Islands in one of the most bitterly contested campaigns of history, wresting air and sea control from the Japanese and providing the Marine Corps and the Army with every possible support as they gained ground inch by inch on the myriad islands.

Assigned the Destroyer Squadron 21 (DesRon 21), O'Bannon played a valiant part in these endeavors, winning a Presidential Unit Citation.

On 7 November at Nouméa, she joined Rear Admiral Daniel J. Callaghan's Support Group, ready to sail with a convoy carrying critical reinforcements, replacements, food, ammunition, and aviation material.

[5] For the next two months, O'Bannon spent most of her time in Vella Gulf, guarding landings, intercepting Japanese troop convoys and their covering escorts, and fighting off air attacks.

The three American ships contacted six enemy destroyers, shrugged at the odds, and raced at 33 knots (61 km/h) to launch torpedoes and open gunfire.

The enemy retired with three newly arrived American destroyers in pursuit, while O'Bannon guarded her stricken sisters, rescuing the survivors of Chevalier.

O'Bannon guarded the Northern Transport area and patrolled the entrances to Leyte Gulf during the battle, coming under air attack.

[1] Through June 1945 O'Bannon operated primarily in the Philippines, serving in the escort or assault force for the long roll call of invasions: Ormoc Bay, Mindoro, Lingayen Gulf, Bataan, Corregidor, Palawan, Zamboanga, Cebu, and Caraboa.

During the Lingayen offensive on 31 January 1945, O'Bannon, with three other destroyers, attacked and sank an enemy submarine; Japanese records studied after the war indicate it was most likely Ro-115.

With the close of the war, O'Bannon patrolled the coast of Honshū until 27 August, when she joined the destroyers Nicholas and Taylor to escort the battleship Missouri into Tokyo Bay, by order of Admiral William Halsey, "because of their valorous fight up the long road from the South Pacific to the very end."

[1] A training period out of Pearl Harbor began upon her return home on 20 June 1952, and she took part in U.S. Atomic Energy Commission operations off Eniwetok.

For O'Bannon, this meant an alternation of roughly six-month deployments to the Far East and periods spent in training operations and necessary overhauls at Pearl Harbor.

While in the Far East, she visited ports in Japan, the Philippines, Taiwan, Australia and New Zealand, with brief, welcome recreation calls at Hong Kong.

She was often in either New Zealand or Australia for the annual commemoration of the Battle of the Coral Sea, a time of national rejoicing in those countries at which Americans are particularly welcome.

O'Bannon first closed the coast of Vietnam during her 1964–65 deployment, when, on 26 December, she left Hong Kong to patrol and conduct hydrographic surveys.

For a week each in May and June, O'Bannon fired shore bombardments, destroying Vietcong base camps, troop concentrations, and small craft.

[1] On 30 January 1970, O'Bannon was decommissioned in a ceremony at Pearl Harbor (side-by-side with her sister Nicholas, as at their launching)[citation needed] and stricken from the Navy List.