sentences:  "Castor" (AKS-1) was launched as SS "Challenger" on 20 May 1939 by Federal Shipbuilding and Dry Dock Co., Kearny, New Jersey, under a Maritime Commission contract; sponsored by Mrs. T. M. Woodward; acquired by the Navy 23 October 1940 and renamed "Castor" six days later; and commissioned 12 March 1941, Commander F. Johnson in command.Clearing Norfolk, Virginia, 6 May 1941, "Castor" arrived at San Diego, California, 20 May to begin a series of cargo voyages to Pearl Harbor.In October, she carried U.S. Marine reinforcements to Johnston Island and Wake Island.