Complex sentence: He led the North Atlantic Neutrality Patrol on increasingly "warlike" operations during the latter part of 1941, and, once war formally began in December, commanded surface forces that escorted convoys and, at times, operated with the British Home Fleet.
Split into simpler sentences: He led the North Atlantic Neutrality Patrol on increasingly "warlike" operations during the latter part of 1941. Once war formally began in December, he commanded surface forces that escorted convoys and, at times, operated with the British Home Fleet.