Complex sentence: Kellett served as president and chairman of the board of Republic Aviation Corporation during World War II. The first autogiro used by the U.S. Postal Service was produced by Kellett and carried the mail between the Camden, New Jersey airport and the roof of the Philadelphia post office.
Split into simpler sentences: Kellett served as president and chairman of the board of Republic Aviation Corporation during World War II. He built the first autogiro used by the U.S. Postal Service. The vehicle carried the mail between the Camden, New Jersey airport and the roof of the Philadelphia post office.