There, through the battles of the Coral Sea and Midway, she offloaded her cargo for transfer to shore depots and issued ammunition to Allied ships, particularly task forces 18, 15, and 16.

Arriving on 11 November, just prior to the Gilbert Islands campaign, she discharged general and ammunition cargo in Havannah Harbor into December.

At the end of May, she was back at Majuro to rearm the fast carrier forces prior to strikes supporting the initial assault on Saipan.

On 30 July, she sailed east again; completed an abbreviated overhaul at San Francisco; filled her holds at Port Chicago; and returned to Eniwetok on 31 October.

The Philippine campaign had started and the fast carrier forces were striking at Japanese positions and shipping from Indochina to the Ryukyus.

As the Military Sea Transportation Service and the Maritime Administration were pressed for cargo space, reserve fleet ships were ordered activated.

Through December of that year and into the summer of 1952, she operated out of Sasebo, carrying her vital cargo to replenishment areas off the coast of the embattled Korean peninsula and to shore facilities at Pohang and Pusan.

In September, she returned to California for an overhaul but was back in Korean waters to resupply United Nations naval forces in early February 1953.

Through 1955, her annual deployments included shuttle runs between Japanese ports and 7th Fleet replenishment areas in waters off Japan and Korea.

In April, she moved to San Francisco for overhaul and, in August, began refresher training with new equipment aboard which increased her underway replenishment capabilities.

Departing Subic Bay on 25 September for her homeport, Rainier touched at Yokosuka, and Pearl Harbor before arriving at Concord on 25 October.

On 21 November, during her sixth line cycle, Rainier established her best underway replenishment record by transferring 826 tons to USS Camden in a 5-hour period.