Dennis David joined the Royal Air Force in 1938, and later that year was posted to his first operational squadron, when he joined No 87 Squadron at Debden, near Saffron Walden flying Hurricanes. The Squadron was posted to France together with No 85 Squadron in September 1939 as part of No 60 Wing in the Air Component of the British Expeditionary Force. The squadrons were stationed at Lille, near the Belgian Border, and saw little action until the German Army began its blitzkrieg through the Netherlands, Belgium and North Eastern France.

During May 1940 the Royal Air Force in France was greatly outnumbered, often 10 to 1 or worse. During this period Dennis David shot down 14 aircraft before suffering from exhaustion due to the intense fighting and was repatriated to England by air ambulance. Upon returning he rejoined No 87 Squadron at Exeter, reforming in preparation for the Battle of Britain. David was in action from July to October 1940 and during this time his score climbed to 20, with many others unconfirmed, as he was always attacked by other enemy fighters before firm claims could be made.

In October 1940, Dennis David was posted to be a Flight Commander in No 213 Squadron, Tangmere where he damaged a Ju88 so badly, that it crash landed in Northern France, taking his tally to over 20 victories.  In November 1940 he was posted to command a Flight of No 152 Squadron, Warmwell flying Spitfires. From 1941 to 1943 Dennis David rose to the rank of Wing Commander and was then posted to the Middle East to command No 89 Squadron flying night-fighting Beaufighters, at Tobruk and Tripoli. In November 1943 he and No 89 Squadron moved to the Far East where he was promoted to Group Captain and took part in the liberation of Burma as SASO 224 Group.

Dennis David continued to serve in the Royal Air Force until his retirement in 1967.  During which time he was appointed Honorary Aide to the Viscount Trenchard, the ‘Father of the Royal Air Force’, from 1954 until the Viscount’s death.  He was also Her Majesty’s Air Attache in Budapest at the time of the Hungarian Uprising and became responsible in assisting 400 people to escape from Hungarian and Russian Secret Police, for this he was knighted by the exiled ruler of Hungary, Grand Duke Arpad of Hapsburg.

In 1993 Dennis David attended the opening of the Battle of Britain Memorial as one of the guests of Her Majesty Queen Elizabeth The Queen Mother.