Complex sentence: McNulty served as a Merchant marine officer from 1917-1920 and with the U.S. Dept. of Navy, where he began as a nautical specialist, from 1920-1937.
Split into simpler sentences: McNulty served as a Merchant marine officer from 1917-1920. Beginning as a nautical specialist, he served with the U.S. Dept. of Navy from 1920-1937.