Complex sentence: At 3:57 am on 8 June the first wave landed on the beach in three landing craft coming ashore unopposed and after advancing a short distance inland established a small perimeter around the beachhead.
Split into simpler sentences: At 3:57 am on 8 June the first wave landed on the beach in three landing craft. They came ashore unopposed and after advancing a short distance inland established a small perimeter around the beachhead.