A. Montagu-Smith joined 99 Squadron on February 29 1936 and was appointed Adjutant in 1938. The squadron was the first to receive Wellingtons and he flew the squadron's first sortie to the German coast in October 1939.
In November he was posted to the Special Duty flight at the A&AEE, Boscombe Down. In April 1940 he went to CGS, Warmwell as a flight Commander and later joined 264 Squadron on September 11 as A Flight Commander.
In December 1940 he was promoted to Squadron Leader and posted to 221 Squadron, as a Flight Commander. He carried out the first Coastal Command Wellington attack on a German U-boat in the Atlantic in May 1941. He then went to a staff job at HQ 18 Group in October 1941.
A year later he took command of 248 Squadron, operating Beaufighters on long-range fighter patrols.
In February 1944 he joined the RAF Delegation in Washington, as Deputy Director RAF Operational Training USA. He returned to the UK and in July 1945 was appointed OC 104 Wing in France, with PR Mosquitos.