Complex sentence: During World War I (1914--18) he served as an aviator, then as under secretary of state for Aviation attempted to make the aircraft industry more effective in delivering planes of the right quality in sufficient numbers.
Split into simpler sentences: During World War I (1914--18) he served as an aviator, then as under secretary of state for Aviation. He tried to make the aircraft industry more effective in delivering planes of the right quality in sufficient numbers.