After undergoing pilot training in Rhodesia, Coulthard deployed to Malta in 1943 and took part in the Invasion of Italy and Operation Dragoon, the Allied invasion of the south of France. He was mentioned in dispatches. Towards the end of the war Coulthard was selected to be part of the initial group of pilots that would transition to Britain's first operational jet fighter, the Gloster Meteor. After the war he was attached to the Central Fighter Establishment and stationed in RAF Wunstorf in Germany, where he took part in the evaluation trials for the de Havilland Venom. In 1955 he became chief instructor at RAF Pembrey. In 1961 he assumed command of RAF Gütersloh. Units under his command were involved in operations related to the Berlin Airlift in 1962.