His education was interrupted by World War I. He and his brother William Burnell Vickers volunteered for service in the army. Geoffrey joined the Sherwood Foresters (7th Robin Hood Battalion) and was in France before the end of 1914 first as a second lieutenant, promoted to temporary captain in 1915 and then to Major and as Second in Command, 1 Bn, The Lincolnshire Regiment in 1918. Explaining his thoughts about going to war, he later wrote "In August Germany invaded Belgium, we had a treaty with Belgium, so we all stopped what we were doing and went off to war. It was as simple as that". He was awarded the Victoria Cross for action in 1915 and the Croix de Guerre (Belgium) in 1918.