Complex sentence: The loss of Kokoda had deprived them of a forward airfield, but to an extent this had been alleviated by the creation of a drop zone around the dry lake at Myola, where supplies were dropped by US transport aircraft.
Split into simpler sentences: The loss of Kokoda had deprived them of a forward airfield. To an extent this had been alleviated by the creation of a drop zone around the dry lake at Myola, where supplies were dropped by US transport aircraft.