Complex sentence: The regimental headquarters was first at Da Nang then in 1966 it was moved to Phu Bai and again 1967 it was moved north to Dong Ha.
Split into simpler sentences: The regimental headquarters was first at Da Nang. Then in 1966 the HQ was moved to Phu Bai and again 1967 it was moved north to Dong Ha.