He transferred to the Royal Air Force when the RNAS and the RFC were merged on 1 April 1918. The creation of the Royal Air Force did not initially have a big impact on Allingham and he later remarked that at that time he still considered himself a navy man. In the RAF he was ranked as a Rigger Aero, Aircraft Mechanic Second Class and was given a new service number: 208317. Allingham returned to the Home Establishment in February 1919 and was formally discharged to the RAF Reserve on 16 April 1919. During the last few years of his life Allingham was recognized as the last surviving founding member of the RAF. Speaking with Dennis Goodwin of the First World War Veterans' Association, Allingham said, "It is a shock as well as a privilege to think that I am the only man alive from that original reorganisation when the RAF was formed."