Complex sentence: Kelly served as the exchange instructor at the British Army's School of Infantry at Warminster between September 1985 and November 1987 and then on promotion to Major commanded a Rifle Company in the 1st Battalion, Royal Australian Regiment from January 1988 until December 1989.
Split into simpler sentences: Kelly served as the exchange instructor at the British Army's School of Infantry at Warminster from September 1985 to November 1987. On promotion to Major, he commanded a Rifle Company in the 1st Battalion, Royal Australian Regiment from January 1988 until December 1989.