The de Havilland DH.98 Mosquito is a British multi-role combat aircraft with a two-man crew which served during and after the Second World War. It was one of few operational front-line aircraft of the era constructed almost entirely of wood and was nicknamed "The Wooden Wonder".[nb 1] The Mosquito was also known affectionately as the "Mossie" to its crews. Originally conceived as an unarmed fast bomber, the Mosquito was adapted to roles including low to medium-altitude daytime tactical bomber, high-altitude night bomber, pathfinder, day or night fighter, fighter-bomber, intruder, maritime strike aircraft, and fast photo-reconnaissance aircraft. It was also used by the British Overseas Airways Corporation (BOAC) as a fast transport to carry small high-value cargoes to, and from, neutral countries, through enemy-controlled airspace. A single passenger could be carried in the aircraft's bomb bay, which would be adapted for the purpose.
When production of the Mosquito began in 1941, it was one of the fastest operational aircraft in the world. Entering widespread service in 1942, the Mosquito was a high-speed, high-altitude photo-reconnaissance aircraft, continuing in this role throughout the war. From mid-1942 to mid-1943, Mosquito bombers flew high-speed, medium or low-altitude missions against factories, railways and other pinpoint targets in Germany and German-occupied Europe. From late 1943, Mosquito bombers were formed into the Light Night Strike Force and used as pathfinders for RAF Bomber Command's heavy-bomber raids. They were also used as "nuisance" bombers, often dropping Blockbuster bombs – 4,000 lb (1,812 kg) "cookies" – in high-altitude, high-speed raids that German night fighters were almost powerless to intercept.
As a night fighter from mid-1942, the Mosquito intercepted Luftwaffe raids on the United Kingdom, notably those of Operation Steinbock in 1944. Starting in July 1942, Mosquito night-fighter units raided Luftwaffeairfields. As part of 100 Group, it was a night fighter and intruder supporting RAF Bomber Command's heavy bombers that reduced bomber losses during 1944 and 1945.[nb 2] As a fighter-bomber in the Second Tactical Air Force, the Mosquito took part in "special raids", such as the attack on Amiens Prison in early 1944, and in precision attacks against Gestapo or German intelligence and security forces. Second Tactical Air Force Mosquitos supported the British Army during the 1944 Normandy Campaign. From 1943, Mosquitos with RAF Coastal Command strike squadrons attacked Kriegsmarine U-boats (particularly in 1943 in the Bay of Biscay, where significant numbers were sunk or damaged) and intercepted transport ship concentrations.
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 South East Asian theatre, and by the Royal Australian Air Force (RAAF) based in the Halmaheras and Borneo during the Pacific War. During the 1950s, the RAF replaced the Mosquito with the jet-powered English Electric Canberra.
Construction concepts pioneered in the de Havilland Comet were later used in the Mosquito.
By the early-mid-1930s, de Havilland had a reputation for innovative high-speed aircraft with the DH.88 Comet racer. The later DH.91 Albatross airliner pioneered the composite wood construction that the Mosquito used. The 22-passenger Albatross could cruise at 210 miles per hour (340 km/h) at 11,000 feet (3,400 m), 100 miles per hour (160 km/h) better than the Handley Page H.P.42 and other biplanes it was replacing.[nb 3] 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 simplified production and reduced construction time.
Air Ministry bomber requirements and concepts
On 8 September 1936, the British Air Ministry issued Specification P.13/36 which called for a twin-engine medium bomber capable of carrying a bomb load of 3,000 pounds (1,400 kg) for 3,000 miles (4,800 km) with a maximum speed of 275 miles per hour (443 km/h) at 15,000 feet (4,600 m); a maximum bomb load of 8,000 pounds (3,600 kg) which could be carried over shorter ranges was also specified. 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.
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 3,000 pounds (1,400 kg) of bombs at a cruising speed of 300 miles per hour (480 km/h). There was support in the RAF and Air Ministry; Captain R N Liptrot, Research Director Aircraft 3 (RDA3), appraised Volkert's design, calculating that its top speed would exceed the new Supermarine Spitfire. There were, however, counter-arguments that, although such a design had merit, it would not necessarily be faster than enemy fighters for long. 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 sometimes acknowledged though it was likely that the Air Ministry envisaged it using light alloy components.
Inception of the de Havilland fast bomber
One of de Havilland's early designs was to adapt the de Havilland Albatross
design to a fast, turret-armed bomber.
Geoffrey de Havilland also believed a bomber with an aerodynamic design, with minimal skin area, was better than the P.13/36 specification. He thought that adapting the Albatross to meet the RAF's requirements 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, Geoffrey 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 there would be shortages of duralumin and steel but should be plenty of wood. Although inferior torsionally, the strength to weight ratio of wood was as good as duralumin or steel, and a different approach to a high-speed bomber was possible.
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 1,500 miles (2,400 km) carrying a 4,000-pound (1,800 kg) bomb load, with a maximum of 260 miles per hour (420 km/h) at 19,000 feet (5,800 m), and a cruising speed of 230 miles per hour (370 km/h) at 18,000 feet (5,500 m). De Havilland believed that much of a compromise, and that getting rid of surplus equipment would lead to a better design. 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 19,000 lb (8,600 kg) it would have a top speed of 300 mph (480 km/h) and cruising speed of 268 mph (431 km/h) at 22,500 ft (6,900 m).
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 a 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 it easier to evade fighters and ground fire. The lack of turrets simplified production 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. Contemporary RAF design philosophy required well-armed heavy bombers more akin to the German schnellbomber. 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 sub-contractor.
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. One design, completed on 6 September, was for an aircraft powered by a single 2,000 hp (1,500 kW) Napier Sabre, with a wingspan of 47-foot (14 m) and capable of carrying a 1,000-pound (450 kg) bomb load 1,500 miles (2,400 km). On 20 September, in another letter to Wilfred 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-engine light bomber with a wingspan of 51 ft 3 in (15.62 m), and powered by Merlin or Griffon engines, the Merlin favoured due to 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.[nb 4] 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.
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, as well as capable of carrying torpedoes. With outbreak of war, the Ministry became more receptive, but still sceptical about an unarmed bomber. It thought the Germans would produce fighters faster than expected. It suggested two forward and two rear-firing machine guns for defence. 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 275 mph (443 km/h) at 15,000 ft (4,600 m) on two-thirds engine power, and a range of 3,000 mi (4,800 km) with a 4,000 lb (1,800 kg) 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 400 mph (640 km/h) at 18,000 ft (5,500 m).
On 12 December, the Vice-Chief of the Air Staff, Director General of Research and Development, Air Officer Commanding-in-Chief (AOC-in-C) of RAF Bomber Command met to finalize the design and decide how to fit it in 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. 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. This was confirmed on 1 January 1940, when Air Marshal 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 1,280 hp (950 kW) Rolls-Royce RM3SM (an early designation for the Merlin 21) with ducted radiators, capable of carrying a 1,000-pound (450 kg) bomb load. The aircraft was to have a speed of 397 miles per hour (639 km/h) at 23,700 feet (7,200 m) and a cruising speed of 327 miles per hour (526 km/h) at 26,600 feet (8,100 m) with a range of 1,480 miles (2,380 km) at 24,900 feet (7,600 m) on full tanks. Maximum service ceiling was to be 32,100 feet (9,800 m).
On 1 March 1940, Air Marshal Roderic Hill issued a contract under Specification B.1/40, for 50 bomber-reconnaissance variants of the DH.98: this contract included the prototype, which was given the factory serial E0234. In May 1940, specification F.21/40 was issued, calling for a long-range fighter armed with four 20 mm cannon and four .303 machine guns in the nose, after which de Havilland were authorized to build a prototype of a fighter version of the DH.98. It was decided after debate that this prototype, given the military serial number W4052, would carry Airborne Interception (AI) Mk.IV equipment as a day and night fighter.[nb 5] By June 1940, the DH.98 had been named "Mosquito". Having the fighter variant kept the Mosquito project alive as there was still criticism within the government and Air Ministry of the usefulness of an unarmed bomber, even after the prototype had shown its capabilities.