With the awarding of the initial Manchester contract expecting 200 aircraft to be delivered in just over 2 years, Avro embarked on a “priority design programme”, committing all efforts to design and production of the new aircraft. As a priority design, the secondary requirements for dive-bombing, torpedo bombing, and catapult launching were removed – simplifying and expediting the design process. Due to the concerns of the availability of the new RR Vulture engine, all initial design work was undertaken using the Bristol Hercules engine, even though the Hercules models then available were 200hp lower than the power promised from mature Vultures. Understood to be a reduced payload airframe until the Vulture was sufficiently developed to be fitted operationally, the reduced payload from a Hercules-powered Manchester was accepted with the initial production aircraft.
The first production Manchester’s rolled from the production line in May 1939, with adequate performance at the accepted lighter weights, but with relatively poor directional stability. Work immediately commenced redesigning the twin vertical tailplanes, quickly leading to an increase in tail height.
As the first Manchester began flight trials, concern from the Air Ministry over bomber defensive armament led to Avro being given instructions to redesign the Manchester to take dorsal and ventral 4 cannon turrets. The revised airframe, with a swollen mid-section to take the 10ft diameter turrets, was designated the Manchester Mk.II and immediately entered production, replacing the Mk.I, with the weight of the new turrets further eroding the available payload. As the Bristol “Ideal” heavy bomber was also to feature the same turrets, the relegation of the Manchester Mk.II to become a complementary medium bomber was considered acceptable to confirm the defensive concept of the heavy turrets.
The first Manchester Mk.II’s were available for delivery to squadrons in December 1939. With the RAF Advanced Air Striking Force deployed in France alongside the British Expeditionary Force, Manchester Mk.II’s were sent directly to the AASF to start replacing Fairey Battles as frontline bombers (after Air Chief Marshall Brooke-Popham’s audit the Fairey Battle was seen as under-armoured and underarmed). Retired Battles were eagerly taken over by Belgium and South Africa. Twelve aircraft were flown directly to Belgium, where the aircraft were not modified to Belgian standard, merely having their RAF roundels overpainted before being sent directly into service.