Gardiner remained in the RAF post-war, being appointed an acting captain for a second time on 1 May 1919, and being made a
Chevalier of the
Legion of Honour, and receiving the
Croix de guerre, from France. while serving with
No. 84 Squadron in Iraq. He then returned to the UK, and was posted as a supernumerary officer at the RAF Depot (Inland Area) on 31 March 1922. On 27 August he was posted to the Headquarters of
No. 7 Group (Inland Area) for personnel staff duties. Gardiner was then assigned to
No. 2 Flying Training School at
RAF Duxford on 1 March 1924. On 28 July 1927 he was assigned to the
Air Ministry to serve in the Directorate of Training, and between 5 July and 10 October 1928 he was seconded for duty in
Estonia. After a short time at the RAF Depot at
RAF Uxbridge, he returned to the Air Ministry Directorate of Training on 21 December 1928. Gardiner was promoted to squadron leader on 14 May 1930, and on 2 January 1931 was posted to
No. 55 Squadron based at
RAF Hinaidi in Iraq. On 23 June he was awarded the Distinguished Service Order "in recognition of gallant and distinguished service in Iraq". Gardiner was posted to No. 4 Flying Training School at
RAF Abu Sueir in Egypt, as Chief Flying Instructor, on 23 October 1934, and also served as an instructor at
RAF Hendon in 1935. In June 1936 he was selected for retention on the active list up to the age of 48, which would be in 1940. On 1 January 1937 he was promoted to wing commander, and on the 11th was appointed commander of
No. 216 (Bomber Transport) Squadron based at
Heliopolis. ==World War II==