In 1977 Mitsubishi embarked on the design of a new business jet known as the MU-300. This aircraft, subsequently called the ‘Diamond’, was a conventional low wing design with a T-tail and two P&W JT15D turbofans mounted on the rear fuselage. For a small jet, it had a large cabin for eight passengers, an aft lavatory and baggage. Initial testing was done in Japan and then the two prototypes were transferred to Mitsubishi’s facility in San Angelo, TX to complete its FAA testing for FAR Part 25. It received its Type Certificate on 6 November 1981. Thereafter, production Diamond Is were assembled in San Angelo from components produced in Nagoya, Japan. By late 1985 Mitsubishi had delivered 100 Diamonds from its San Angelo facility. At that time Mitsubishi sold the MU-300 package to Beechcraft where it became known as the Beechjet 400.