Improved aircraft designs were in the offing with the Bristol Beaufighter, then under development. It would prove formidable, but its development was slow. The Beaufighter had a maximum speed of 320 mph (510 km/h), an operational ceiling of 26,000 ft (7,900 m) and a climb rate of 2,500 ft (760 m) per minute. Its armament of four 20 mm (0.79 in) Hispano cannon and six .303 in Browning machine guns offered a serious threat to German bombers. On 19 November, John Cunningham of No. 604 Squadron RAF shot down a bomber flying an AI-equipped Beaufighter. It was the first air victory for the airborne radar.