The Boulton Paul Defiant was a test of the idea of a 'turret fighter' whose offensive armament was located in a powered turret. The theory was that this would make for a much more effective aircraft, especially against bombers, as the guns would be free to fire on whatever enemy plane was around and not just the one in front. When first set upon by the Luftwaffe, the result was a lot of German planes knocked out of the skies. It was decided that perhaps it would make for a good night fighter. Defiant I airframes equipped with an early AI Mk IV radar system were sent into the night skies. While not exactly the outstanding success that all had hoped, it did achieve some success with the first kill being in December of 1940.