The Second World War cut short Hapgood's playing career (he was only 30 when hostilities broke out). Hapgood served in the Royal Air Force during the war, whilst also playing for Arsenal and England in unofficial matches. In June 1940, he was one of five Arsenal players who guested for Southampton in a victory over Fulham at Craven Cottage.[6] He also appeared as a guest player for West Ham United later in Second World War.[7] It was during the war that Hapgood fell out with the Arsenal management, after he was loaned out to Chelsea[8] and eventually left the club under a dark cloud.