The Defiant Mk II was soon paired with the newly developed airborne interception radar (AI) to become a night fighter. While initial AI equipment was too heavy and bulky to be practical for equipping smaller aircraft, the improved AI Mk. IV radar was suitably sized for the Defiant; the first such equipped Defiants were introduced in late 1941. Later versions of the AI radar were adopted over time, such as the AI Mk VI. The need for both the Defiant and the Hurricane in the night fighter role petered out by 1942 as the larger Bristol Beaufighter became the RAF's primary night fighter type, freeing both aircraft for other duties.