The de Havilland DH.98 Mosquito was a British multi-role combat aircraft, with a two-man crew, that served during the Second World War and the postwar era. The Mosquito was one of the few operational, front-line aircraft to be constructed almost entirely of wood and, as such, was nicknamed "The Wooden Wonder". It was also known affectionately as the "Mossie" to its crews Originally conceived as an unarmed fast bomber, the Mosquito was adapted to many other roles during the air war, 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 transport.
When the Mosquito entered production in 1941, it was one of the fastest operational aircraft in the world. Entering widespread service in 1942, the Mosquito first operated as a high-speed, high-altitude photo-reconnaissance aircraft, and continued to operate in this role throughout the war. From mid-1942 to mid-1943 Mosquito bombers were used in high-speed, medium- or low-altitude missions, attacking factories, railways and other pinpoint targets within Germany and German-occupied Europe. From late 1943, Mosquito bomber units 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 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 was used to intercept Luftwaffe raids on the United Kingdom, most notably defeating the German aerial offensive, Operation Steinbock, in 1944. Offensively, starting in late 1942, some Mosquito night-fighter units conducted intruder raids over Luftwaffe airfields and, as part of 100 Group, the Mosquito was used as a night fighter and intruder in support of RAF Bomber Command's heavy bombers, and played an important role in reducing bomber losses during 1944 and 1945.[nb 1] 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 other precision attacks against Gestapo or German intelligence and security forces. 2 TAF Mosquitos also played an important role operating in tactical support of the British Army during the 1944 Normandy Campaign. From 1943 Mosquitos were used by RAF Coastal Command strike squadrons, attacking Kriegsmarine U-boats (particularly in the 1943 Bay of Biscay offensive, where significant numbers of U-boats were sunk or damaged) and intercepting transport ship concentrations.
The Mosquito saw service with the Royal Air Force (RAF) and many other air forces in the European theatre, and the Mediterranean and Italian theatres. The Mosquito was also used by the RAF in the China, Burma, India (CBI) Theatre, and by the Royal Australian Air Force (RAAF) based in the Halmaheras and Borneo during the Pacific War.
Construction concepts pioneered in the de Havilland Comet were later used in the Mosquito.
By the early-mid 1930s, de Havilland established a reputation for innovative high-speed aircraft with the DH.88 Comet racer, while the later DH.91 Albatross airliner successfully pioneered the composite wood construction that the Mosquito would use. The 22-passenger Albatross could cruise at 210 miles per hour (340 km/h) at 11,000 feet (3,400 m), a vast improvement on the 100 miles per hour (160 km/h) Handley Page H.P.42 and other biplanes it was replacing. 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-engined 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. Major 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, who was the chief designer of Handley Page, put forward to the Air Ministry the concept of a fast unarmed bomber. In his 20-page document, Volkert laid out plans for an aerodynamically clean medium bomber that would carry 3,000 pounds (1,400 kg) of bombs at a cruising speed of 300 miles per hour (480 km/h). There was some support for the idea in the RAF and Air Ministry; for example a Captain Liptrot, who was then Research Director Aircraft 3 (RDA3), appraised Volkert's design, calculating that its top speed would exceed that of the brand new Supermarine Spitfire. There were, however, counter-arguments that, although such a design had merit, it would not necessarily maintain a speed advantage over enemy fighters for long. The Ministry was also considering the use of non-strategic materials for aircraft production, which, in 1938, led to specification B.9/38 and the development of the Albemarle medium bomber, which was largely constructed from spruce and plywood attached to a steel-tube frame. Thus it can be seen that the idea of a small, fast bomber, possibly made out of non-strategic materials, was already gaining support at a much earlier stage than is sometimes acknowledged.
Inception of the De Havilland fast bomber
One of de Havilland's early design concepts was to adapt the de Havilland Albatross
design to become a fast, turret-armed bomber.
Another designer who believed that meeting the P.13/36 specification would lead to a mediocre aircraft was Geoffrey de Havilland, who felt that an aerodynamically clean design, with minimal skin area, was a good concept for a bomber. He initially thought that adapting the Albatross airliner to meet the RAF's requirements was a time-saving possibility. In April 1938, performance estimates were produced of a twin Rolls-Royce Merlin powered DH.91, with the Bristol Hercules and Napier Sabre as alternatives. On 7 July 1938, Geoffrey de Havilland sent a letter to Air Marshal Wilfred Freeman, the Air Council's member for Research and Development, discussing the specification and arguing that in the event of war, there would be shortages of materials such as duralumin or steel, while there should be plentiful supplies of wood. Additionally, although inferior torsionally, the strength to weight ratio of wood was as good as that of duralumin or steel, and, given such considerations, a different approach to designing a high-speed bomber was possible.
After further consideration, in a follow-up letter sent to Freeman on 27 July, de Havilland stated that the P.13/36 specification could not be met by a twin Merlin powered aircraft and that either the top speed or load carrying 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 lb (1,800 kg) bomb load, with a maximum speed 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 such a concept was too much of a compromise, and that getting rid of some surplus equipment would lead to a better design. On 4 October 1938, for example, de Havilland projected the performance of another design based on the D.H 91 Albatross, powered by two Merlin Xs, with a three-man crew and armed with 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 pounds (8,600 kg) it would have a top speed of 300 miles per hour (480 km/h) and cruising speed of 268 miles per hour (431 km/h) at 22,500 feet (6,900 m).
Still believing that this performance could be improved upon, and after examining more concepts based on the Albatross and the new all-metal DH.95 Flamingo, de Havilland settled on designing a completely new aircraft that would be aerodynamically clean, of wooden construction and powered by the Merlin, which offered promise of substantial future development. The new design would be faster than all current or foreseeable enemy fighter aircraft, and could dispense with a defensive armament, which would only slow it down and make interception or losses to anti-aircraft guns more likely. Instead, high speed and good manoeuvrability would make it easier for the design to evade both fighters and ground fire. Also, the lack of turrets meant that production would be simplified and production time reduced, with a delivery rate far in advance of any competing designs. Without armament, the crew could be reduced to a pilot and a navigator. This was in contrast to contemporary RAF design philosophy, which required well-armed heavy bombers and was much more akin to the German schnellbomber concept. However, during a meeting held in early October 1938 between Geoffrey de Havilland, Charles C Walker (de Havilland's chief engineer) and Air Ministry officials, the latter showed little interest in de Havilland's concept 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 both single- and twin-engined variations of light-bomber designs using different engines, while 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 lb (450 kg) bomb load 1,500 miles (2,400 km). On 20 September, in another letter to Wilfred Freeman, Geoffrey 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 either Merlin or Griffon engines, with the Merlin being favoured because of its immediate availability.
On 5 October 1939, with the Second World War a month old, the nucleus of a design team under the leadership of Eric Bishop, de Havilland's chief designer, moved to the security and secrecy of Salisbury Hall and started work on what was now known as the DH.98.[nb 2] With an eye to making the DH.98 more versatile, Bishop made provision for four 20 mm cannon which could be installed in the forward half of the bomb bay, immediately under the cockpit, and firing via blast tubes and troughs under the forward fuselage.
The DH.98 was still too radical for the Air Ministry, which continued to want a heavily armed, multi-role aircraft, combining medium bomber, reconnaissance and "general purpose" roles, as well as being capable of maritime strike, for which torpedo carrying equipment was specified. With the outbreak of the war, the Air Ministry became more receptive, but were still sceptical about sanctioning an unarmed bomber and thought that the Germans would produce fighters which were faster than expected. Instead, the Ministry asked de Havilland to compromise and suggested two forward and two rear firing machine guns for defence. The Air Ministry also opposed a two-man bomber, wanting at the very least a third crewman to reduce the workload of the others on long flights. The Air Council then added further requirements, such as remotely controlled guns, a top speed of 275 miles per hour (443 km/h) at 15,000 feet (4,600 m) on two-thirds engine power, and a range of 3,000 miles (4,800 km) with a 4,000 lb (1,800 kg) bomb load. To appease the Air Ministry, de Havilland built several mock-ups with a gun turret just aft of the cockpit, but, apart from this compromise, de Havilland made no changes to the fundamentals of the design.
On 12 November, at a meeting considering fast bomber ideas put forward by de Havilland, Blackburn, and Bristol, Marshal W. 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 for a slightly larger Griffon powered aircraft, armed with a four-gun tail turret, were presented, Freeman was able to get the requirement for defensive weapons dropped, and a draft requirement was raised calling for a high-speed light reconnaissance bomber capable of 400 miles per hour (640 km/h) at 18,000 feet (5,500 m).
One month later, on 12 December 1939, 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 finalise the details of the design and decide how it was to fit within the RAF's strategic aims. The AOC-in-C still would not accept an unarmed bomber, but insisted it would be suitable for reconnaissance missions with either F8 or F24 cameras. After representatives of the company, the Air Ministry and the RAF's operational commands had examined a full scale mock-up at Hatfield on 29 December 1939, the project finally received official backing. This was confirmed on 1 January 1940, when Air Marshal Freeman chaired another meeting with Geoffrey de Havilland, John Buchanan, (Deputy of Aircraft Production) and John Connolly, who was Buchanan's chief of staff. Claiming the DH.98 was the "fastest bomber in the world", de Havilland added "it must be useful". Freeman supported its production for RAF service and ordered a single prototype for an unarmed bomber variant 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 (experimental designation for what became known as the Merlin 21) with ducted radiators, capable of carrying a 1,000 lb (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 20mm cannon and four .303 machine guns in the nose, after which de Havilland were authorised to build a prototype of a fighter version of the DH.98. It was decided after some debate, that this prototype, given the serial number W4052, would carry Airborne Interception (AI) Mk.IV equipment as a day and night fighter.[nb 3] By June 1940, the DH.98 had been given the name "Mosquito". Having the fighter variant helped keep the Mosquito project alive because there was still plenty of criticism over the usefulness of an unarmed bomber within the government and Air Ministry, even after the first prototype had flown and shown its capabilities.