Complex sentence: Until then the 7th Parachute Battalion had been leading the brigade but the 13th Battalion then took over and secured the high ground overlooking the village of Erle, which was captured that night by the 12th Parachute Battalion.
Split into simpler sentences: Until then the 7th Parachute Battalion had been leading the brigade but the 13th Battalion then took over and secured the high ground overlooking the village of Erle. Which was captured that night by the 12th Parachute Battalion.