De Havilland conceived the idea of a wooden aircraft to take advantage of the underused resources and skills of the furniture industry at a time of great pressure on the conventional aircraft industry, and shortages of steel and aluminium. The Air Ministry was not interested; de Havilland designed the Mosquito on a speculative basis, only interesting the Ministry when they saw the performance of the prototype.
The original Mosquito design dated from 1938 but it was not until March 1940 that there was sufficient interest in the aircraft for construction to commence. Three prototypes were built, each with a different configuration. The first to fly was the bomber prototype W4050 on November 25, 1940 followed by the night fighter model on May 15, 1941 and the photo-reconnaissance model on June 10, 1941.
The outstanding feature of the Mosquito was its speed, faster than any other aircraft of the time-so much so that defensive armament was not fitted as the Mosquito could outrun any pursuer.
The photo-reconnaissance model became the basis for the PR Mk I Mosquito while the bomber model became the B Mk IV, of which 273 were built. The first operational sortie by a Mosquito was made by a PR Mk I on September 20, 1941.
The Mk IV entered service in May 1942 with No.105 Squadron. The B Mk IV could accommodate 4 × 500 lb. (227 kg) bombs in the bomb bay, and either two drop tanks or two additional 500 lb. bombs on wing hardpoints. The Mk IX was a high-altitude bomber variant but the most numerous bomber version was the Mk XVI of which about 1,200 were built.
The Mosquito bombers could carry a 4,000 lb. (1 816 kg) “blockbuster” bomb in their internal bomb bay. This required a bulged bomb bay which could alternatively accommodate up to 6 × 500 lb. bombs on an Avro carrier. Mosquitos were widely used by the RAF Path Finder Force which marked targets for night-time strategic bombing. Despite an initially high loss rate the Mosquito ended the war with the lowest loss rate of any aircraft in RAF Bomber Command service. The RAF found that when finally applied to bombing, it had proved 4.5 times cheaper than the Lancaster in terms of useful damage done, and they have never specified a defensive gun on a bomber since. Special Luftwaffe units formed to fight the Mosquito attacks were rather unsuccessful, and the Luftwaffe considered the Mosquito a superior implementation of their own “Schnellbomber” concept.
The first production night fighter Mosquitos were designated the NF Mk II and 466 were built with the first entering service with No.157 Squadron in January 1942, replacing the Douglas A-20 Havoc. They were armed with four 20 mm Hispano cannons mounted in the lower front fuselage and four .303 in (7.7 mm) Browning machine guns in the nose as well as an AI Mk IV radar. The success of these night fighters, and the need to conceal the existence of radar, resulted in a degree of notoriety for pilot John “Cat’s Eyes” Cunningham; he and other pilots were said untruly to have phenomenally acute night vision due to eating carrots (This was due to a British disinformation campaign arising from the aforesaid need to hide the development of radar from the Germans).
Ninety-seven NF Mk IIs were upgraded with a centrimetric AI Mk VIII radar and these were designated the NF Mk XII. The NF Mk XIII, of which 270 were built, was the production equivalent of the Mk XII conversions. They also dispensed with the machine guns in the nose. The other night fighter variants were the Mk XV, Mk XVII (converted Mk IIs), Mk XIX and Mk 30. The last three marks mounted the US-built AI Mk X radar. After the war, two more night fighter versions were developed, the NF Mk 36, powered by the Merlin 113/114 engine, and the NF Mk 38 using the British-built AI Mk IX radar. To warn German night fighters that they were being tracked by these radars, the Germans introduced Naxos ZR radar detectors.
Mosquito night intruders of No.100 Group RAF, Bomber Command, were also fitted with a device called “Serrate” to allow them to track down German night fighters from their Lichtenstein B/C and SN2 radar emissions, as well as a device named “Perfectos” that tracked German IFF.