Complex sentence: The main body of the battalion remained in Darwin, forming part of the town's defensive garrison, until late October 1940, when they were relieved by the 2/25th Battalion, and embarked again on the "Zealandia".
Split into simpler sentences: The main body of the battalion remained in Darwin, forming part of the town's defensive garrison. They were relieved by the 2/25th Battalion in late October 1940, and embarked again on the "Zealandia".