For those new to the Boulton-Paul "Defiant"...
In the mid 1930s, there emerged great enthusiasm for a 2 seat fighter in which all of the armament would be concentrated in a power-operated turret. Such a fighter (protagonists claimed) would be able to tear through enemy bomber streams and wreak havoc.
The first two "defiant" prototypes flew in August 1937 with a 768 kW Rolls Royce Merlin I inline engine, and once the usual bugs were worked out, the "Defiant" F.m.k.I entered service in December of 1939.
After early encounters with the luftwaffe, in which the Defiant scored some success because of its unusual layout, further operations quickly revealed the deficiencies of the type, vis-a-vis, turret weight and drag which impaired its dogfighting ability and also left the pilot without any fixed forward firing armament.
It was then decided to convert all existing fighters to the night fighter standard, with the prototype AI.Mk 6 radar.
Total production run of all types was 1075