He was posted to France on the 24th August 1915. He was wounded in the left shoulder by a shell explosion and was evacuated to Bethnal Green Hospital to recover. Although he returned to France in July 1918, it is claimed that his arm was practically useless. He was reported Missing in action on the 1st October 1918 when his Battalion were engaged in attacking he village of Rumilly. As the Battalion made their attack they came across stiff resistance from Germans located in Rumilly Trench and Rumilly Support Trench. As consequence, the Battalion lost the advantage of the British artillery barrage and were forced into a heavy fight with the German troops. Although the position was eventually won, the Battalion suffered a high level of casualties with 31 Kille, 97 Wounded and 50 Missing. One of those missing was Ernest Williamson. His body was never found, and his name is recorded on the Vis-En-Artois memorial.