A development of the Type 142M was the Type 149 which Bristol named the Bolingbroke, retrospectively changed by the Air Ministry to Blenheim Mk IV and the Type 142M to the Blenheim Mk I. Fairchild Canada built the Type 149 under licence as the Bolingbroke. Blenheims Mk I and the Mk IV were adapted as fighters by the addition of a gun pack of four Browning .303 machine guns in the bomb bay. The Mk IV was used as a long range fighter and as a maritime patrol aircraft; both aircraft were also used as bomber/gunnery trainers.