Complex sentence: At 19, he worked as a medic in the French Resistance army, was in charge of a psychiatric hospital, and then served 39 months stationed in the South Pacific in the United States Army Air Corps.
Split into simpler sentences: At 19, he worked as a medic in the French Resistance army, where he was in charge of a psychiatric hospital. He then served 39 months stationed in the South Pacific in the United States Army Air Corps.