Complex sentence: The Division was on the Normandy coast when the invasion took place, and thus fought in the early days of the Battle of Normandy, quickly becoming trapped in the Cotentin as U.S. forces sealed off the Peninsula the remnants of the Division fell back on Cherbourg.
Split into simpler sentences: The Division was on the Normandy coast when the invasion took place, and thus fought in the early days of the Battle of Normandy, quickly becoming trapped in the Cotentin. As U.S. forces sealed off the Peninsula, the remnants of the Division fell back on Cherbourg.