When Airbus designed the Airbus A300 during the 1970s it envisioned a broad family of airliners to compete against Boeing and McDonnell Douglas, two established US aerospace manufacturers. From the moment of formation, Airbus had begun studies into derivatives of the Airbus A300B in support of this long-term goal. Prior to the service introduction of the first Airbus airliners, Airbus had identified nine possible variations of the A300 known as A300B1 to B9. A tenth variation, conceived in 1973, later the first to be constructed, was designated the A300B10. It was a smaller aircraft that would be developed into the long-range Airbus A310. Airbus then focused its efforts on the single-aisle market, which resulted in the Airbus A320 family, which was the first digital fly-by-wire commercial aircraft. The decision to work on the A320, instead of a four-engine aircraft proposed by the Germans, created divisions within Airbus. As the SA or "single aisle" studies (which later became the successful Airbus A320) underwent development to challenge the successful Boeing 737 and Douglas DC-9 in the single-aisle, narrow-body airliner market, Airbus turned its focus back to the wide-body aircraft market.