Following a Bermuda shakedown cruise, "Marsh" conducted training exercises and escorted convoys along the northeast coast. On 25 March, she steamed from New York, heading for Plymouth, England, on her first trans-Atlantic convoy. She returned to the East Coast on 1 May, and on 23 May, sailed for the coast of North Africa. The destroyer escort accompanied two more convoys between those coasts before being assigned to the Mediterranean Theater. Entering the Mediterranean through the Strait of Gibraltar on 9 July, "Marsh" escorted convoys between North Africa, Malta, and southern Italy until mid-August. On 14 August, she sailed from Naples with the assault forces for "Operation Dragoon", the invasion of Southern France. She remained in the Mediterranean for the next month providing gunfire support and convoying supplies in the area.