Complex sentence: The raceway occupies a portion of Hendricks Field--currently an active airport for private and commercial traffic--but formerly, a United States Army Air Forces training base during 1941 to 1946, where pilots learned to fly the B-17 Flying Fortress.
Split into simpler sentences: The raceway occupies a portion of Hendricks Field, a former military training base and currently an active airport for private and commercial traffic. From 1941 to 1946, pilots learned to fly the B-17 Flying Fortress.