Complex sentence: He abandoned the sledge at Boat Harbour beside the base, and when "Aurora" returned to Cape Denison for the final time on 13 December 1913, only the engine and propeller were taken back to Australia.
Split into simpler sentences: He abandoned the sledge at Boat Harbour beside the base. When "Aurora" returned to Cape Denison for the final time on 13 December 1913, only the engine and propeller were taken back to Australia.