Complex sentence: The battalion spent the next year in training for airborne operations, which included getting used to jumping with only one parachute instead of two and through a hole in the floor of the aircraft, instead of through a door of a C-47 Dakota.
Split into simpler sentences: The battalion spent the next year in training for airborne operations. Major differences between their previous American training and the new regime included jumping with only one parachute, and doing it through a hole in the floor of the aircraft, instead of through the door of a C-47 Dakota.