Complex sentence: The 3205th Drone Group was the post-World War II operator of surplus B-17G Flying Fortress aircraft that were modified during the postwar years for use as radio-controlled drones for various tests, usually as targets for missiles.
Split into simpler sentences: The 3205th Drone Group operated obsolete aircraft during the 1950s as radio-controlled drones for various tests. It was the primary post-World War II operator of surplus B-17G Flying Fortress aircraft that were modified usually as targets for missiles.