Complex sentence: From March 1944, the squadron took part in ground assault operations in preparation for the invasion of Normandy in June that year, after which it provided air support to the advancing Allied armies through France, the Low Countries and finally Germany.
Split into simpler sentences: From March 1944, the squadron took part in ground assault operations in preparation for the invasion of Normandy in June that year. It afterwards provided air support to the advancing Allied armies through France, the Low Countries and finally Germany.