Complex sentence: BAC argued against the proposal in favour of their BAC Three-Eleven project, intended as a large wide-bodied airliner like the Airbus A300, Douglas DC-10 and Lockheed TriStar.
Split into simpler sentences: BAC argued against the proposal in favour of their BAC Three-Eleven project. It was intended to be a large, wide-bodied airliner, like the Airbus A300, Douglas DC-10 and Lockheed TriStar.