Complex sentence: When World War II broke out, Graham used his hobby to serve his country, first serving as a flying instructor in Uvalde, teaching raw recruits the basics of flying and preparing them for the extreme pressures of combat.
Split into simpler sentences: When World War II broke out, Graham used his hobby to serve his country. Initially he served as a civilian flying instructor in Uvalde, teaching raw recruits the basics of flying and preparing them for the extreme pressures of combat.