Monadnock, launched as SS Cavalier in 1938 by Pusey and Jones Corp., Wilmington, Delaware, was acquired by the U.S. Navy through purchase from the Philadelphia and Norfolk Steamship Company, Philadelphia, Pennsylvania, on 9 June 1941; converted at the Bethlehem Steel Co., Atlantic Works, East Boston, Massachusetts; and commissioned as the Coastal Minelayer Monadnock (CMc-4), 2 December 1941, Lt. Comdr. Frederick O. Goldsmith in command.