Sentinel reported for duty with the Atlantic Fleet on 15 January 1943. The minesweeper experienced her first enemy contact on 20 February while escorting Merak (AF-21) from Bermuda to Norfolk, Virginia when an escorting aircraft dropped a smoke bomb 2,500 yards astern. Picking up suspected submarine wake noise with her echo-ranging equipment, Sentinel attacked on two contacts within a 25-minute period. There was no evidence of damage to the enemy, except for some dark brown or black matter which appeared after the second starboard depth charge exploded.