In late August 1918, Forsyth was on a temporary attachment to the 2nd Battalion, Auckland Infantry Regiment, during the early stages of the Hundred Days Offensive. He was on probation for a commission in his unit and his attachment to the battalion was to gain front-line experience. On 24 August 1918, during the Second Battle of Bapaume, the battalion was ordered to capture of the village of Grévillers. On reaching the outskirts of the village, German machine gun fire prevented any further forward movement. Forsyth, scouting ahead of his platoon, made contact with two British tanks and despite being exposed to the German machine guns, guided them in, providing covering fire for the New Zealanders. One tank was soon crippled by artillery fire. Despite having been wounded in the arm, he assisted its crew to evacuate the tank and then organised them, along with several other soldiers, into a flanking party to attack the machine gun nest holding up the advance. The Germans shortly withdrew and the advance was able to continue. Forsyth set about organising defensive positions but was fatally shot by a sniper.