Born in Winchester on 27 November 1927 to the son of Royal Air Force Wing Commander he was educated at Bridlington School, East Riding of Yorkshire, and joined the RAF as an aircraft apprentice in February 1944.

At this point, he missed his first opportunity for an RAF commission, being very unlucky not to be selected for a cadetship.

Dunn won his colours every year in rugby and cricket, excelling to win the Victor Ludorum shield for outstanding sportsmanship.

Due to his efforts Dunn, then a corporal, was award the British Empire Medal (BEM).

After returning to England in 1951, Dunn was selected for a commission within the engineering branch of the RAF.