On 7 June, in the battle of Messines Ridge, immediately the barrage lifted, Carroll rushed an enemy trench and bayoneted four men, then rescued a comrade who was in difficulties. Later in the advance he attacked a machine-gun crew of four, killing three of the crew and capturing the gun, and, in spite of heavy shelling and machine-gun fire, dug out two members of his battalion who had been buried by a shell explosion. During the battle, his battalion was in action for four days and Carroll exhibited courage and fearlessness throughout.