Complex sentence: Fighting from four hilltops, surrounded, and outnumbered nearly ten to one, U.S. forces caused heavy losses on eight enemy battalions, before an aerial withdrawal under heavy mortar, anti-aircraft, and small arms fire.
Split into simpler sentences: Fighting from four hilltops, surrounded, and outnumbered nearly ten to one, U.S. forces caused heavy losses on eight enemy battalions. US forces then executed an aerial withdrawal under heavy mortar, anti-aircraft, and small arms fire.