After
shakedown,
Onslow departed the
United States West Coast on 19 March 1944. She stopped at
Pearl Harbor,
Hawaii, and
Majuro before reporting for duty with
Task Group 57.3 at
Kwajalein.
The seizure of Ujelang On 20 April 1944,
Onslow was given the task of seizing
Ujelang, a small island in the
Marshall Islands occupied by
Japanese troops. Embarking troops of the
United States Armys
111th Infantry Regiment she rendezvoused with
minesweeper USS YMS–91 on 21 April 1944. On the morning of 22 April 1944, 160
soldiers were put ashore to capture the island. They met resistance at the center of the island from 18 entrenched Japanese soldiers, who were killed, with no
American casualties. During this time,
Onslow came under attack by a twin-engined
Mitsubishi G4M "Betty"
bomber, which she drove off with 5-inch (127 mm)
antiaircraft fire.
Operations at Kwajalein and Eniwetok Onslow returned to Kwajalein on 25 April 1944 and spent the next six weeks there engaged in
seaplane tending duties. She then was sent to
Eniwetok, arriving there on 10 June 1944.
Supporting landings on Saipan On 15 June 1944, in company with destroyer ,
Onslow escorted seaplane tender to
Saipan. While on this passage she rescued a downed
fighter pilot who was adrift in a
raft, off Saipan. On 18 June 1944, three days after the initial landings on Saipan,
Onslow took up duties tending the seaplanes of
Patrol Squadron 16 (VP-16). On the morning of 10 September 1944, two Japanese swam from Saipan and succeeded in climbing aboard one of the moored seaplanes undetected. They proceeded to blow the plane up with
hand grenades, and
Onslow dispatched a boat to assist the planes crew. The boat was driven back under fire, but two additional boats joined in and they were then able to reach the plane and kill the boarders. However, gunfire set the plane's fuel ablaze, destroying it, although its crew was saved.
Operations in the Palau Islands Onslow and seaplane tenders USS
Pocomoke, , , and departed Saipan on 12 September 1944 to participate in the
invasion of the
Palau Islands. At
noon on 16 September 1944 the formation entered
Naval Base Kossol Passage. The five ships tended seaplanes there under adverse conditions that included floating
mines, dangerous
coral heads, and rough water, not to mention the presence of enemy
airplanes and
submarines. On 13 November 1944,
Onslow sped out to recover a
Martin PBM Mariner flying boat down at sea with engine failure and towed it to
Ulithi Atoll. She then returned to Kossol Passage. On 12 January 1945, three Japanese
midget submarines entered the harbor, and the ships spent the day dodging coral heads trying to ferret out the elusive little submarines. One of the midget submarines was sunk; the other two escaped.
Operations at Saipan On 17 January 1945,
Onslow moved to Ulithi Atoll, and on 19 January 1945 she steamed for
Guam. She then spent two months at Saipan beginning on 20 January 1945, providing services to
CASU 48 bowser boats and the crews of two
crash boats.
Supporting the invasion of Okinawa On 23 March 1945,
Onslow got underway for the invasion of
Okinawa. Along with seaplane tenders USS
Yakutat, , and , she escorted seaplane tenders , , and USS
Chandeleur from Saipan to
Kerama Retto, arriving there on 28 March 1945. Upon
anchoring, the ships began to lay out a
seadrome and by 29 March 1945, were operating on a regular schedule with 60 PBM Mariner seaplanes.
Onslows work at Kerama Retto was more difficult than ever before. Many of the seaplanes were damaged by the Japanese or by heavy seas. Because of their frequency, it became necessary for the seaplane tenders to ignore Japanese air raids at times. On one occasion
Onslow assisted in shooting down a Japanese fighter which was making a dive on her. Beginning about 1 June 1945, many of Japanese troops isolated on the small islands off Okinawa began coming to the
beaches to surrender. When they did,
Onslow notified the proper commands and often furnished shallow-
draft boats to assist the U.S. Army in picking up the surrendering Japanese. On 6 August 1945,
Onslow received orders to escort
Chandeleur to Eniwetok via Saipan. She transferred all patrol squadron personnel and equipment to seaplane tender and departed Okinawa. Hostilities with Japan ceased and
World War II came to an end on 15 August 1945, the same day she entered port at Eniwetok.
Honors and awards Onslow earned four
battle stars for her service in World War II, for: • Marshall Islands operation, March 1944-April 1944 •
Marianas operation: Capture and occupation of Saipan, 14 June 1944 – 27 August 1944 • Western
Caroline Islands operation: Capture and occupation of southern Palau Islands, 16 September 1944 – 13 November 1944 •
Okinawa Gunto operation: Assault and occupation of
Okinawa Gunto, 28 March 1945 – 6 August 1945 ==Peacetime service 1945-1947==