In September 1939 Great Britain entered the Second World War prompting McManners immediately to volunteer for military service. He joined his local regiment the Royal Northumberland Fusiliers, where he made his name as a winger in their soccer team, and completed basic training. However, when the Army realised he had recently been awarded a first-class honours degree, the Regiment shelved its plans for him to become a driving instructor. Instead he was sent to the OCTU at Fenham Barracks where he was put through basic training for a second time, and was commissioned. McManners served in the Western Desert Campaign and was at the Siege of Tobruk. He was made Adjutant of the First Battalion, under Commanding Officer Lt Col Forbes -Watson.