Complex sentence: Dr. J. Cromwell served as acting superintendent until 1964 when Dr. Leonard Lavis was appointed who in turn resigned in 1969 and was replaced by Dr. William Campbell.
Split into simpler sentences: Dr. J. Cromwell served as Acting Superintendent until 1964 when Dr. Leonard Lavis was appointed. Dr. Lavis resigned in 1969 and was replaced by Dr. William Campbell.