Complex sentence: Van Haren, Jr. completed his naval aviation training in 1942, however, he was such a good pilot that the Navy made him a flight instructor and he spent over a year teaching other Naval aviators how to fly.
Split into simpler sentences: Van Haren, Jr. completed his naval aviation training in 1942. However, he was considered to be such a good pilot that the Navy made him a flight instructor and he spent over a year teaching other Naval aviators how to fly.