Upon retiring from the military in December 1968, Dunn became a guest conductor with the City of Birmingham Symphony Orchestra. He also recorded with the Light Music Society Orchestra. In 1969, he received an EMI Golden Disc for sales of more than one million Royal Marines Band records. In the same year, he was also elected an honorary member of the American Bandmasters Association. In 1987, he received the Sudler Medal of the Order of Merit from the John Philip Sousa Foundation. He became the Founder President of the International Military Music Society in 1976, a position which he held until his death. In 1988, after serving as the Senior Warden, Dunn became the first military musician to be installed as the Master of the Worshipful Company of Musicians.