Complex sentence: There he met the man who was to be his best friend and neighbor, Commander Johnny Olson, who had joined the Navy as a Ship's Carpenter in 1903 and was now the Commander of the Aircraft Repair and Overhaul Unit.
Split into simpler sentences: There he met the man who was to be his best friend and neighbor, Johnny Olson. CDR Olson had joined the Navy as a Ship's Carpenter in 1903 and was now the Commander of the Aircraft Repair and Overhaul Unit.