During an engagement with the enemy Mactier, who had been sent forward as a runner to investigate, ran to a barricade. He threw a bomb, climbed over the wire, closed with and killed the machine-gun garrison of eight men with revolver and bombs, and threw the enemy gun over the parapet. He rushed forward another twenty metres and jumped into the middle of another garrison of six men who surrendered immediately. He charged at third post, bombing and killing the garrison. He was attacking a fourth enemy position when a machine-gun swung round and killed him instantly.