The de Havilland DH.98 Mosquito was a British twin-engined, multi-role combat aircraft, introduced during the Second World War. Unusual in that its airframe was constructed mostly of wood, it was nicknamed the "Wooden Wonder",Price 2009, p. 3. or "Mossie".Hanson, Dave. "deHavilland DH 98 Mosquito"; . warbirdalley.com. In 1941, it was one of the fastest operational aircraft in the world..
Originally conceived as an unarmed fast bomber, the Mosquito's use evolved during the war into many roles, including low- to medium-altitude daytime tactical bomber, high-altitude night bomber, pathfinder, day or night fighter, fighter-bomber, intruder, maritime strike, and photo-reconnaissance aircraft. It was also used by the British Overseas Airways Corporation as a fast transport to carry small, high-value cargo to and from neutral countries through enemy-controlled airspace.Sharp and Bowyer 1971, p. 338. The crew of two, pilot and navigator, sat side by side. A single passenger could ride in the aircraft's bomb bay when necessary.
The Mosquito FB Mk. VI was often flown in special raids, such as Operation Jericho (an attack on Amiens Prison in early 1944), and precision attacks against military intelligence, security, and police facilities (such as Gestapo headquarters). On 30 January 1943, the 10th anniversary of Hitler being made chancellor and the Nazis gaining power, a morning Mosquito attack knocked out the main Berlin broadcasting station while Hermann Göring was speaking, taking his speech off the air.
The Mosquito flew with the Royal Air Force (RAF) and other air forces in the European, Mediterranean, and Italian theatres. The Mosquito was also operated by the RAF in the Southeast Asian theatre and by the Royal Australian Air Force based in the Moluccas and Borneo during the Pacific War. During the 1950s, the RAF replaced the Mosquito with the jet-powered English Electric Canberra.
Development
By the early to mid-1930s, de Havilland had built a reputation for innovative high-speed aircraft with the DH.88 Comet racer. Later, the DH.91 Albatross airliner pioneered the composite wood construction used for the Mosquito. The 22-passenger Albatross could cruise at at , faster than the Handley Page H.P.42 and other biplanes it was replacing.Stroud 1990, p. 369. The wooden monocoque construction not only saved weight and compensated for the low power of the de Havilland Gipsy Twelve engines used by this aircraft, but also simplified production and reduced construction time.Bowman 2005, p. 9.
Air Ministry bomber requirements and concepts On 8 September 1936, the British Air Ministry issued Specification P.13/36, which called for a twin-engined medium bomber capable of carrying a bomb load of for with a maximum speed of at ; a maximum bomb load of carried over shorter ranges was also required.Sharp and Bowyer 1971, p. 30. Aviation firms entered heavy designs with new high-powered engines and multiple defensive turrets, leading to the production of the Avro Manchester and Handley Page Halifax.Sharp and Bowyer 1971, p. 31.
In May 1937, as a comparison to P.13/36, George Volkert, the chief designer of Handley Page, put forward the concept of a fast, unarmed bomber. In 20 pages, Volkert planned an aerodynamically clean, medium bomber to carry of bombs at a cruising speed of . Support existed in the RAF and Air Ministry; Captain R. N. Liptrot, Research Director Aircraft 3, appraised Volkert's design, calculating that its top speed would exceed that of the new Supermarine Spitfire, but counter-arguments held that although such a design had merit, it would not necessarily be faster than enemy fighters for long.Buttler 2004, pp. 76–77. The ministry was also considering using non-strategic materials for aircraft production, which, in 1938, had led to specification B.9/38 and the Armstrong Whitworth Albemarle medium bomber, largely constructed from spruce and plywood attached to a steel-tube frame. The idea of a small, fast bomber gained support at a much earlier stage than is sometimes acknowledged, though the Air Ministry likely envisaged it using light alloy components.Buttler 2004, pp. 74, 77.
Inception of the de Havilland fast bomber
Based on his experience with the Albatross, Geoffrey de Havilland believed that a bomber with a good aerodynamic design and smooth, minimal skin area, would exceed the P.13/36 specification.. Furthermore, adapting the Albatross principles could save time. In April 1938, performance estimates were produced for a twin Rolls-Royce Merlin-powered DH.91, with the Bristol Hercules (radial engine) and Napier Sabre (H-engine) as alternatives. On 7 July 1938, de Havilland wrote to Air Marshal Wilfrid Freeman, the Air Council's member for Research and Development, discussing the specification and arguing that in war, shortages of aluminium and steel would occur, but supplies of wood-based products were "adequate". Although inferior in tension, the strength-to-weight ratio of wood is equal to or better than light alloys or steel, hence this approach was feasible. Lord Beaverbrook, Minister of Aircraft Production, nicknamed it "Freeman's Folly", alluding to Air Chief Marshal Sir Wilfrid Freeman, who defended Geoffrey de Havilland and his design concept against orders to scrap the project.
A follow-up letter to Freeman on 27 July said that the P.13/36 specification could not be met by a twin Merlin-powered aircraft and either the top speed or load capacity would be compromised, depending on which was paramount. For example, a larger, slower, turret-armed aircraft would have a range of carrying a 4,000 lb bomb load, with a maximum of at , and a cruising speed of at . De Havilland believed that a compromise, including eliminating surplus equipment, would improve matters. On 4 October 1938, de Havilland projected the performance of another design based on the Albatross, powered by two Merlin Xs, with a three-man crew and six or eight forward-firing guns, plus one or two manually operated guns and a tail turret. Based on a total loaded weight of , it would have a top speed of and cruising speed of at .
Still believing this could be improved, and after examining more concepts based on the Albatross and the new all-metal DH.95 Flamingo, de Havilland settled on designing a new aircraft that would be aerodynamically clean, wooden, and powered by the Merlin, which offered substantial future development. The new design would be faster than foreseeable enemy fighter aircraft, and could dispense with defensive armament which would slow it and make interception or losses to anti-aircraft guns more likely. Instead, high speed and good manoeuvrability would make evading fighters and ground fire easier. The lack of turrets simplified production, reduced drag, and reduced production time, with a delivery rate far in advance of competing designs. Without armament, the crew could be reduced to a pilot and navigator. Whereas contemporary RAF design philosophy favoured well-armed heavy bombers, this mode of design was more akin to the German philosophy of the Schnellbomber.Batchelor and Lowe 2008, p. 5. At a meeting in early October 1938 with Geoffrey de Havilland and Charles Walker (de Havilland's chief engineer), the Air Ministry showed little interest, and instead asked de Havilland to build wings for other bombers as a subcontractor.Batchelor and Lowe 2008, p. 6.
By September 1939, de Havilland had produced preliminary estimates for single- and twin-engined variations of light-bomber designs using different engines, speculating on the effects of defensive armament on their designs.Buttler 2004, p. 78. One design, completed on 6 September, was for an aircraft powered by a single Napier Sabre, with a wingspan of and capable of carrying a bomb load . On 20 September, in another letter to Wilfrid Freeman, de Havilland wrote "…we believe that we could produce a twin-engine bomber which would have a performance so outstanding that little defensive equipment would be needed." By 4 October, work had progressed to a twin-engined light bomber with a wingspan of and powered by Merlin or Griffon engines, the Merlin favoured because of availability. On 7 October 1939, a month into the war, the nucleus of a design team under Eric Bishop moved to the security and secrecy of Salisbury Hall to work on what was later known as the DH.98.Sharp and Bowyer 1971, p. 34. For more versatility, Bishop made provision for four 20 mm cannon in the forward half of the bomb bay, under the cockpit, firing via blast tubes and troughs under the fuselage.Bowman 2005, p. 11.
The DH.98 was too radical for the ministry, which wanted a heavily armed, multi-role aircraft, combining medium bomber, reconnaissance, and general-purpose roles, that was also capable of carrying torpedoes. With the outbreak of war, the ministry became more receptive, but was still sceptical about an unarmed bomber. They thought the Germans would produce fighters that were faster than had been expected.Sharp and Bowyer 1971, pp. 31–32, and suggested the incorporation of two forward- and two rear-firing machine guns for defence.Bowman 2005, p. 10. The ministry also opposed a two-man bomber, wanting at least a third crewman to reduce the work of the others on long flights. The Air Council added further requirements such as remotely controlled guns, a top speed of at 15,000 ft on two-thirds engine power, and a range of with a 4,000-lb bomb load. To appease the ministry, de Havilland built mock-ups with a gun turret just aft of the cockpit, but apart from this compromise, de Havilland made no changes.
On 12 November, at a meeting considering fast-bomber ideas put forward by de Havilland, Blackburn, and Bristol, Air Marshal Freeman directed de Havilland to produce a fast aircraft, powered initially by Merlin engines, with options of using progressively more powerful engines, including the Rolls-Royce Griffon and the Napier Sabre. Although estimates were presented for a slightly larger Griffon-powered aircraft, armed with a four-gun tail turret, Freeman got the requirement for defensive weapons dropped, and a draft requirement was raised calling for a high-speed, light-reconnaissance bomber capable of at 18,000 ft.Buttler 2004, p. 79.
On 12 December, the Vice-Chief of the Air Staff, Director General of Research and Development, and the Air Officer Commanding-in-Chief (AOC-in-C) of RAF Bomber Command met to finalise the design and decide how to fit it into the RAF's aims. The AOC-in-C would not accept an unarmed bomber, but insisted on its suitability for reconnaissance missions with F8 or F24 cameras.Bowman 2005, p. 12. After company representatives, the ministry, and the RAF's operational commands examined a full-scale mock-up at Hatfield on 29 December 1939, the project received backing.Buttler 2004, p. 80. This was confirmed on 1 January 1940, when Freeman chaired a meeting with Geoffrey de Havilland, John Buchanan (Deputy of Aircraft Production), and John Connolly (Buchanan's chief of staff). De Havilland claimed the DH.98 was the "fastest bomber in the world… it must be useful". Freeman supported it for RAF service, ordering a single prototype for an unarmed bomber to specification B.1/40/dh, which called for a light bomber/reconnaissance aircraft powered by two Rolls-Royce RM3SM (an early designation for the Merlin 21) with ducted radiators, capable of carrying a bomb load. The aircraft was to have a speed of at and a cruising speed of at with a range of at on full tanks. Maximum service ceiling was to be .