Complex sentence: A fourth company was also detached at this time to the Milne Bay area to improve the base's facilities; it remained in New Guinea until October 1943 before returning to Australia for rest and reorganisation.
Split into simpler sentences: A fourth company was also detached at this time to the Milne Bay area to improve the base's facilities. They remained in New Guinea until October 1943 before returning to Australia for rest and reorganisation.