Complex sentence: He joined the CID in 1961 and was promoted Detective Sergeant (1964), Detective Inspector (1968), Detective Chief Inspector (1974), and at the age of 38 he became the youngest Detective Chief Superintendent in Britain (1978).
Split into simpler sentences: He joined the CID in 1961 and was promoted to the ranks of Detective Sergeant (1964), Detective Inspector (1968) and Detective Chief Inspector (1974). At the age of 38 he became the youngest Detective Chief Superintendent in Britain (1978).