 Complete the following phrase:  The first to be used operationally was the Aeronca GB-1, essentially an autopilot attached to a small glider airframe carrying a bomb. It was intended to allow the 8th Air Force bombers to drop their payloads far from their targets and thus avoid having to overfly the most concentrated areas of anti-aircraft artillery fire. It was first used on 28 May 1944 against the Eifeltor marshalling yard in 