The Defender was the first fighter aircraft to serve with the Krakabloa Air Arm. The need for a fighter arose from the heavy losses being sustained by 'Conveyor' bomber aircraft which were flying unescorted to their targets on the Wright Isles and so the defender was designed to provide fighter cover after a failed earlier attempt to produce a fighter aircraft. There was a great amount of redesign and modification between the first mark of Defender and the last.

The d model featured increased power output from the engine, a new four bladed propellor and the ability to carry an external fuel tank to extend range, which became useful in the desert war.