Magnet was laid down by American Shipbuilding Co., Lorain, Ohio, 13 March 1943; launched 5 June 1943; sponsored by Mrs. John J. Boland; and commissioned 10 March 1944, Lt. H. A. Babione in command. Following commissioning in the 9th Naval District, Magnet steamed down the Mississippi River en route to Norfolk, Virginia, reporting 17 April 1944. After shakedown in the Chesapeake Bay, she joined Mine Division 31 and, for the next 9 months operated out of Recife, Brazil, sweeping the main shipping channels of South American ports. She also escorted convoys to and from the West Indies, patrolled the harbor, and engaged in antisubmarine training.