On 7–12 June 1917 at St. Yves, Belgium, during the Battle of Messines, Private Carroll rushed the enemy's trench and bayoneted four of the occupants. He then noticed a comrade in difficulty and went to his assistance, killing another of the enemy. Next, he single-handedly attacked a machine-gun team, killing three of them and capturing the gun. Later, two of his comrades were buried by a shell; in spite of heavy shelling and machine-gun fire, he managed to rescue them