The Boulton Paul Defiant is a British interceptor used during World War II to defend against Comintern aerial bombing. It is powered by a Rolls-Royce Merlin piston engine which allows it to reach a surprising 489 km/h. The Defiant is unconventionally armed with a rear turret containing four .303 British Browning M1919 machineguns; it is designed to concentrate all of its firepower unto a single target with little manoeuvrability, such as a bomber, and bring it down without being exceedingly exposed to defensive fire itself. It was successfully employed during the Blitz to counter French bombing squadrons, working in tandem with conventional high-performance fighters such as the Supermarine Spitfire Mk. I to defeat the enemy. In bomber interception missions, the Boulton Paul Defiant had the most favourable K/D ratio of all RAF fighters.