The fifth ship to be named Mercury by the Navy, AK-42 was launched as SS Lightning by Federal Shipbuilding & Dry Dock Go., Kearny, New Jersey, 15 July 1939; sponsored by Mrs. Royal S. Copeland; purchased on the ways by Moore McCormack Lines and placed in operation by them as SS Mormactern 30 October 1940; acquired by the Navy 20 June 1941; converted, and commissioned as Mercury 1 July 1942, Lt. Comdr. G. W. Graber, UK MERCHANT FLEET, in command.