In 1934 the British Air Ministry issued a requirement for a heavy bomber as one of the steps in the British rearmament program, The new aircraft would be a cantilever monoplane of all metal construction, with advanced features for the time, such as and enclosed flight deck, retractable landing gear, trailing-edge flaps on the inboard sections of the main wings and inboard stowage of the bombs, together with turreted defensive armament. The power plant was to consist of two high-powered piston driven engines with variable pitch propellers.

The resulting design by Armstrong-Whitworth was ordered straight off the drawing board by the RAF and the first prototype, the Mk I, flew in 1936. Successive variants followed, with the Mk V being the definitive model. The original engines were replaced in the Mk III by two Merlin IV engines rated at 1030 hp at 16,000 feet that drove three-blade constant speed Rotol propellers.

One can see the genesis of the Avro Lancaster in the lines and overall design of the Whitley bomber, with the long rectangular fuselage and twin vertical tail planes. It was an amazingly modern aircraft for its time, although it quickly became outmoded by further overall design improvements in bomber design by all nations. One of its innovations was a two-speed supercharger fitted on the engines of the Mk II, the first used on an RAF operational aircraft.

When the Mk V came along, the increased power of its engines enable the designers to add increased defensive armament by adding a gun turret in the tail position which required lengthening the fuselage and better nose-position quarters for the bombardier with a flat-aiming panel. The rear gun turret was a Frazer-Nash power operated unit that featured four 0.303 (7.7 mm) Browning machine guns. Further design changes in the Mk V included straight leading edges to the two vertical tail planes to replace the original curved surfaces which gave better dynamic stability with increased airflow over the rudder surfaces, inflatable rubber boots on the mainplane leading edges for de-icing and fuel capacity was significantly increased.

Delivery of the Mk V Whitleys coincided with the time of the German invasion of the Low Countries and France. The Whitley Mk V was one the five warplane types (the others were the Hurricane and Spitfire fighters and the Bristol Blenheim and Vickers Wellington heavy bombers) that received the highest possible production priority in an attempt to boost the UK's offensive and defensive capabilities.

The Whitley Mk V was designated by the RAF as a long range night bomber. It carried a crew of five; the pilot, co-pilot, the wireless operator/navigator, the nose-gunner/bombardier and the tailgunner. Its maximum level speed was 230 mph, with a service ceiling of 26,000 feet and typical range of 1650 miles. Its length was 70 ft 6 in, wing span of 84 ft and a height of 15 feet. Empty it weighed in at 19,350 lbs and its maximum takeoff weight was 33,500 lbs.

The last Whitley Mk V was delivered in June 1943. With it's relatively low speed it was entrusted with night operations with a few notable exceptions. One such being the "thousand bomber" raid on Koln, in May of 1942, a month after the Whitley had been withdrawn from first-line service. It served out the remainder of it flying days in maritime reconnaisance and advanced bomber training.

The Whitley was never especially successful as a night bomber, but did achieve a number of notable "firsts"; one of the first to drop bombs on German proper in WW II, first British bomber over Berlin on a leaflet dropping mission and the first RAF bomber to attack Italy after its entry into the war in June 1940.