The Mk.II (H.P-59) entered service in July 1941; the main difference to the Mk.I was an additional anti-aircraft gun tower, giving it a better defensive armament. The Mk.III appeared in August 1943 and was equipped with more powerful Bristol Hercules radial engines and it had a greater wingspan. The Mk.IV remained an unfinished project. The next variants were the Mk.V with 1,675 hp Hercules 100 engines and the Mk.VII, which was powered by the same Hercules engines as the Mk.III. These were the last bomber variants and thus only small numbers have been built.