Complex sentence: Starting at dawn however, the RAF made eight sorties low into the valley and when they got through, the hair-pin road along which the Axis transport was concentrated was pock-marked with bomb craters along with many burning vehicles.
Split into simpler sentences: Starting at dawn however, the RAF made eight sorties low into the valley. When they attacked, the hair-pin road along which the Axis transport was concentrated was pock-marked with bomb craters along with many burning vehicles.