Complex sentence: As a civilian in the post-WWII years, he worked as an oil company troubleshooter, but he rejoined the Navy in the 1950s and was flying carrier-based reconnaissance attack jets over Vietnam in the 1960s.
Split into simpler sentences: As a civilian in the post-WWII years, he became an oil company troubleshooter. He rejoined the Navy in the 1950s and flew carrier-based reconnaissance attack jets over Vietnam during the 1960s.