Mountrail was laid down 24 June 1944, under Maritime Commission (MARCOM) contract, MCV hull 561, by Permanente Metals Corporation, Yard No.

[3] Mountrail departed Kerama Retto and arrived San Francisco 22 May, to load troops for the Philippines, whom she disembarked at Manila.

[3] With the outbreak of the Korean War, Mountrail recommissioned 9 September 1950, and sailed 22 December, for the Far East to carry men between Japan and Korea until returning San Diego 2 August 1951.

[3] Mountrail returned to Long Beach in December and trained on the West Coast until sailing for Japan 28 November 1953.

During training, she operated in the Atlantic and Caribbean, strengthening American forces at Guantánamo Bay during the Cuban Missile Crisis of fall 1962.

In October and November 1964 she took part in NATO landing exercises in southern Spain, and 8 February 1965, she left Norfolk, Virginia for her first deployment with the 6th Fleet.

Mountrail was laid up in the National Defense Reserve Fleet, James River Group, Lee Hall, Virginia.