Lansdowne first operated along the Atlantic seaboard on shakedown, antisubmarine and escort duty, and attacked an enemy submarine off Cape Hatteras 3 July. Following a severe depth charge attack, large quantities of oil bubbled to the surface and it was presumed the submarine had been sunk. Arriving at Cristobal, Canal Zone 13 July, the destroyer was sent to a position where PC-458 had located an enemy submarine. Upon arrival, Lansdowne launched a depth charge attack. Large quantities of oil rose to the surface, and the forward motion of the submarine ceased. Postwar records established that U-153 was sunk by these attacks.
On 21 August Lansdowne transited the Panama Canal and headed for the South Pacific. En route to Tonga, she rescued the pilot and radioman of a splashed observation plane from South Dakota (BB 57).
Arriving Nukualoia Bay 6 September, the destroyer joined TF 18, under Radm. Leigh Noyes in Wasp (CV 7). On 15 September 1942. Wasp was torpedoed and heavily damaged. Immediately Lansdowne headed for the carrier at flank speed. On her way a torpedo wake passed directly beneath her bow and under almost her entire length. The destroyer headed toward the source of the wake seeking the enemy submarine, but was ordered to assist the carrier, which was now burning furiously. After she had rescued about 460 bluejackets, Lansdowne was ordered to sink Wasp. Three of her torpedoes exploded in the carrier and Wasp sank that night at 2100.
Lansdowne, with TG 64.1, took part in the occupation of Funafuti, Ellice Islands 2 October, then escorted aircraft ferry Hammondsport (APV 2) to Espiritu Santo. From 13 October the ship screened various task forces, groups, and units in the British Solomons, escorted damaged ships to safety, and on 30 November sighted and bombarded a large group of Japanese landing barges, sinking several and scoring direct hit on a beached enemy ship east of Cape Esperance. She also shelling shore installations from Bahi to Visale.
On 31 November, Lansdowne made three attacks against a submerged target west of Koli Point, bringing diesel oil, slabs of cork, and air bubbling to the surface. In December, she made an escort run from Tulagi to Sydney and Auckland, returning to Nouméa. Continuing to serve in the Solomons, Lansdowne grounded in the Russell Islands 26 February and sailed 11 March for repairs at San Francisco.
From May to July, the ship operated in the Aleutians, bombarding Kiska 6 July. She headed back to Espiritu Santo from Pearl Harbor 20 July, and joined an anti shipping force off Vella Lavella 2 September. Escort duty in the Solomons and to Fiji continued until 29 October, Buka-Bonis (1 to 2 November) and Rabaul (6 and 11 November). While covering landing operations at Empress August Bay, 28 November, the ship repelled an enemy air attack and two days later bombarded Bougainville which she hit again late in December. During January and February 1944, Lansdowne covered the landings at Torokina, Bougainvllle and Green Island, and conducted anti shipping sweeps between Buka and Rabaul. On 18 February the destroyer bombarded and torpedoed shipping at Karavia Bay in the first surface action against Rabaul. Numerous fires were started ashore and on the shipping. On the nights of 24 and 25 February, Lansdowne sank a 6,800-ton Japanese cargo ship about 20 miles north of New Hanover. Early the following morning she opened fire on shore emplacements and shipping at Kavieng, silencing a large coastal gun and several other batteries and sinking one ship while setting fire to two others.
After operating northwest of the Admiralties, Lansdowne joined TFs 77 and 78 for the initial landings in the Aitape-Hollandia-Tanahmerah area of northern New Guinea and launched air attacks on Palau, Yap, Ulithi, and other enemy bases in the central Pacific 3 March through 1 April. The ship then returned to Pearl Harbor for refit, arriving 18 May.
Lansdowne arrived at Majuro 5 June and next day joined TF 58 for the Marianas operation through June and July, thus participating in the raids on [the Bonins] 15 and 18 June, the Battle of the Philippine Sea 19 and 20 June, and the assaults on Guam and Tinian.
On 30 July, the destroyer sailed for overhaul at Bremerton, returning to Ulithi 29 October. On patrol and escort in the western Carolines until 5 May 1945, she then steamed to the Ryukyus for duty off Okinawa. She patrolled antisubmarine stations around the island complex, gave fire support, and screened carriers.
Lansdowne next operated with the Third Fleet off Japan, screening logistics groups and fast carriers launching strikes against the enemy homeland. The ship was detached from the task force 20 to 23 August to transport the Atomic Bomb Investigation Group to Okinawa and then proceeded to Sagami Wan, arriving 27 August.
On 29 August, Lansdowne escorted battleship South Dakota, Adm. Chester Nimitz’s flagship, into Tokyo Bay and then operated with units of the Allied Prisoner of War Rescue Group evacuating prisoners from camps in southern Honshu. The ship was detached 2 September 1945 to transfer Japanese emissaries from Yokohama to battleship Missouri in Tokyo Bay for the official surrender ceremonies, returning the party to Yokohama the same day. She operated out of Yokohama until sailing 15 October from Wakanoura for the United States via Singapore, Colombo and Capetown, arriving Brooklyn Navy Yard December 1945.
Lansdowne departed for Charleston, South Carolina, 17 January 1946 and decommissioned to enter the Atlantic Reserve Fleet there 2 May 1946. On 10 June 1949 the ship was transferred to the Turkish Navy, in which she served as Gaziantep (D-344) until 1973.