Complex sentence: After the operation, the Allies worked to repair the heavily damaged Japanese airfields, while they switched their efforts to landing operations around Saidor, beginning early January 1944 as part of the next stage of wider operations in New Guinea.
Split into simpler sentences: After the operation, the Allies worked to repair the heavily damaged Japanese airfields. Meanwhile they switched their efforts to landing operations around Saidor, beginning early January 1944 as part of the next stage of wider operations in New Guinea.