She was acquired by the US Navy from the Maritime Commission on 25 March 1943 and launched the same day, sponsored by Lieutenant (junior grade) Doris M. Yetter, NC, USN, who had been a prisoner of war on Guam in 1941.

On 26 October she sailed for the Admiralties, via Kossol Roads, Palau, Caroline Islands, arriving at Manus to disembark the wounded for transfer to base hospitals.

She arrived off Okinawa the morning of 19 April in company with USS Solace (AH-5) to remain for four days at Hagushi Beach embarking patients despite frequent air raids and threat of kamikazes.

On 19 August she embarked the 227th Station Hospital assigned to the Korean Occupation Forces, and three days later departed for Korea via Okinawa, arriving Jinsen 9 September.

Mercy decommissioned at San Francisco, California, 17 May, was delivered to the War Department the same day, and transferred to the US Army 20 June for further service as a hospital ship.