Complex sentence: Staff were moved to empty families' quarters on the base and contingencies were implemented; when Air Marshal Sir John Sutton was appointed Commander in January 1986, he was faced with a burnt out HQ which would eventually cost £10 million to fix.
Split into simpler sentences: Staff were moved to empty families quarters on the base and contingencies were implemented. By the time a new commander arrived in January 1986 (Air Marshal Sir John Sutton) he was faced with a burnt out HQ which would eventually cost £10 million to fix.