The Defiant Mk1 is a British World War II-era two-seat, single-engine, day / night military interceptor developed by Boulton Paul Aircraft. The Defiant took its maiden flight on August 11, 1937, and it entered service in December of 1939. Boulton Paul Aircraft manufactured just over 1,000 of the design. Only one non-flying example remains in existence, as a static museum display.
In the mid-1930s, the Royal Air Force sought to procure a new type of aircraft that could defend against raids comprising masses of unescorted long-range German bombers. This concept culminated in the April 1935 Air Ministry release of Specification F.9/35. This outlined a two-seat, day / night interceptor aircraft comprising a powered, freely rotating turret with 360-degree field of fire that housed an array of machine guns. Such an aircraft would, as per the specification, engage bombers in formation from aside and from beneath them.
Called a “turret fighter,” the Boulton Paul Defiant was constructed with aluminum skin over a metal airframe. It has a low-wing cantilever monoplane design with a standard empennage and a retractable standard undercarriage. The electro-hydraulically turret is mounted just behind the cockpit on the dorsal aspect of aircraft. When operational, the turret comprised four parallel-mounted .303-caliber Browning machine guns and accommodated a single gunner.
Upon its debut, the Boulton Paul Defiant proved successful against unescorted German bombers. However, the Germans quickly learned to counter the aircraft by attacking it head-on, as it did not possess any forward-firing armament. The Royal Air Force withdrew the fighter from daytime use, focusing on nighttime missions, including missions that used onboard radar. These radar-equipped Defiants made critical defensive contributions to the effort against the German “Blitz” of 1940 to 1941. In the latter days of the war, the Defiant was used for gunnery training and search and rescue missions.
The Defiant Mk1 measures 35 feet, 4 inches in length, stands 11 feet, 4 inches tall, and has a wingspan of 39 feet, 4 inches. When operational, it was powered by a single Rolls-Royce Merlin III V12 engine that produced up to 1,030 horsepower and turned a 3-blade, constant-speed propeller. The Defiant had a maximum range of 500 miles, a service ceiling of 31,000 feet above sea level, and a maximum climb rate of 2,000 feet per minute. It cruised at 175 miles per hour and had a top speed of 304 miles per hour.
