Complex sentence: At 9 a.m. the brigade's advance guard occupied a position on a wooded height overlooking the Red River above the village of Trung Xa, whose plateau, thickly covered in tall umbrella pines, offered an ideal observation post and firing platform for the French artillery.
Split into simpler sentences: At 9 a.m. the brigade's advance guard occupied a position on a wooded height overlooking the Red River above the village of Trung Xa. The Trung Xa plateau, thickly covered in tall umbrella pines, offered an ideal observation post and firing platform for the French artillery.