de Havilland DH98 Mosquito

Officials in the British Air Ministry vehemently resisted building it, but from the day production finally began in 1941 until the war ended, the Royal Air Force never had enough Mosquitoes to perform the amazing variety of missions that air tacticians devised for this outstanding airplane. It excelled at day and night bombing from high or very low altitudes, long-range reconnaissance, air-to-air combat in daylight and darkness, and finding and striking distant targets at sea. No less than forty-two distinct versions of the D. H. 98 entered service. At extreme speeds, Mosquitoes carried heavy loads great distances because of two key design features: a lightweight, streamlined, wooden airframe propelled by powerful, reliable engines. The "Wooden Wonder" was constructed from Alaskan spruce, English ash, Canadian birch and fir, and Ecuadorian balsa glued and screwed together in new, innovative ways, and motivated by the world's finest reciprocating, liquid-cooled power plants, a pair of Rolls Royce Merlins. There has never been a more successful, combat-proven warplane made of wood.

The Mosquito descended from civilian, not military designs. In 1934, de Havilland decided to construct a new airplane to compete in the England-Australia Air Race. In only ten months, the firm designed and built three D.H. 88 Comet racers. Pilots raced all three against sixty-four entrants from thirteen countries. A Comet won the 17,710-km (11,000-mile) race in 71 hours and another finished fourth but the third Comet dropped out because of engine trouble. An advanced plywood skin formed the wing and fuselage of these twin-engine airplanes and de Havilland used the same technology to build Mosquito wings.

A more direct ancestor to the D. H. 98 was the de Havilland DH 91 Albatross air transport. After much official delay, de Havilland built seven of these four-engine airliners and Imperial Airways bought five and began to fly them on scheduled routes in December 1938. World War II completely overshadowed the world-class speed and economical performance of the Albatross but its impact on Mosquito development was profound. In both airplanes, radiators mounted inside the wings cooled the engines. Thin slots cut into the wing leading edges allowed cooling air to flow through these radiators. This was a significant improvement because on older aircraft such as the Spitfire, the radiators hung beneath the lower wing surface and the drag generated by this arrangement robbed the Spitfire of precious speed. The Mosquito shared another Albatross trait. Design engineer Arthur E. Hagg conceived of a lightweight, strong composite wooden construction technique to build the Albatross fuselage. He left de Havilland in 1937 but the company used his composite construction methods again on Mosquitoes.

Nazi aggression escalated during the late 1930s. With every act of terror, Geoffrey de Havilland (founder and head of the firm) and his design staff became more convinced that they could create an exceptional warplane based on the Comet and Albatross. The members of the Mosquito design team included the chief designer and team leader, R. E. Bishop, Richard M. Clarkson, assistant chief engineer and Mosquito aerodynamicist, C. T. Wilkins, assistant chief designer and the fuselage specialist, W. A. Tamblin, senior designer and the wing specialist, and Fred Plumb who managed constructing the prototype. Their thoughts coalesced in 1938 to focus on the design of a high-speed, unarmed bomber. The new design would weigh thousands of pounds less than conventional bombers armed with enclosed, power-driven turrets and heavy machine guns, its finish smooth and streamlined enough to speed past all pursuers, even the most advanced, single-engine fighters. For two years, de Havilland and the Air Ministry argued over several different designs and government specifications for the new airplane. Doubts racked most ministry officials about committing national resources to build a small, unarmed bomber out of wood. The notion ran counter to aeronautical trends in every other nation worldwide but in addition to speed, de Havilland's idea had other advantages. Wood, and the skilled personnel required to work it, was plentiful while aluminum was in dangerously short supply and aircraft metalworkers were already consumed with producing Spitfires, Hurricanes, and other metal airplanes.

De Havilland finally won a contract to build a prototype five months after Hitler invaded Poland but the Air Ministry, and many people in the British aircraft industry, remained skeptical right up until March 3, 1941. On that day government test pilots, conducting official trials with the Mosquito prototype, published a favorable report on the aircraft. From this time forward, official doubt turned to quiet confidence.

Like the Comet and Albatross wings, de Havilland built Mosquito wings out of shaped pieces of wood and plywood cemented together with Casein glue. Approximately 30,000 small, brass wood screws also reinforced the glue joints inside a Mosquito wing (another 20,000 or so screws reinforced glue joints in the fuselage and empennage). The internal wing structure consisted of plywood box spars fore and aft. Plywood ribs and stringers braced the gaps between the spars with space left over for fuel tanks and engine and flight controls. Plywood ribs and skins also formed the wing leading edges and flaps but de Havilland framed-up the ailerons from aluminum alloy and covered them with fabric. Sheet metal skins enclosed the engines and metal doors closed over the main wheel wells when the pilot retracted the landing gear.

To cover the wing structure and add strength, de Havilland woodworkers built two top wing skins and one bottom skin using birch plywood. The top skins had to carry the heaviest load so the designers also beefed them up with birch or Douglas fir stringers cut into fine strips and glued and screwed between the two skins. The bottom skin was also reinforced with stringers. Together the top and bottom skins multiplied the strength of the internal spars and ribs. A Mosquito wing could withstand rigorous combat maneuvering at high G-loads when the airplane often carried thousands of additional pounds of fuel and weapons. To maintain strength, trim weight, and speed fabrication time, the entire wing was finished as a single piece, wingtip to wingtip, with no break where the wing bisected the fuselage. A finished and painted wing was light and strong with a smooth surface unblemished by drag-inducing nail or rivet heads.

De Havilland engineers and technicians used generally the same techniques to build the Comet, Albatross, and Mosquito wings out of wood and plywood. When they designed and built the fuselage, however, they copied the methods and materials employed to build the Albatross fuselage. This airliner was the product of the brilliant mind of Arthur E. Hagg, de Havilland's Chief Draftsman in 1937. He left the company that same year but his ideas lived on in the Mosquito. Hagg created a light, strong, very streamlined structure by sandwiching 9.5 mm (three-eighths inch) Ecuadorian balsa wood between Canadian birch plywood skins that varied in thickness from 4.5 mm to 6 mm (about ¼ inch). The plywood/balsa/plywood sandwich was formed inside concrete molds of each fuselage half, and each mold held seven birch plywood formers reinforced with spruce blocks, plus bulkheads, floors, and other structural members. As the glue cured, metal clamps held the skin layers tight to the mold. Technicians finished the edge of each half of the fuselage with male and female wedge joints as fitters attached wiring and other equipment to the inner walls. Final fuselage assembly was reminiscent of a typical plastic model airplane kit as the two halves were glued and screwed together. Fabricators completed the final step in building the fuselage when they covered it with Mandapolam. To build the empennage, workers framed the rudder and elevator out of aluminum and covered them with fabric but they built the vertical and horizontal stabilizers from wood.

The first Mosquito prototype flew on November 24, 1940. Flight trials revealed only minor development problems and de Havilland finished twenty production aircraft before 1941 ended. A photo-reconnaissance D. H. 98 flew the first operational Mosquito sortie to survey the western part of the border between France and Spain on September 17, 1941. Bomber and fighter versions began operating in early 1942 and Mosquitoes soon swept across the length and breadth of Western Europe.

As a bomber, the Mosquito was fast enough to excel at precision attacks against heavily defended targets. Courageous crews often flew these raids at altitudes of 15-50 meters (49-164 feet). Flying this type of raid in a single-engine airplane would border on suicide but the Mosquito's twin Merlins doubled the crew's chances of surviving engine failure. Nonetheless, on numerous occasions, anti-aircraft gunfire or patrolling German fighters splintered Mosquito airframes. Men of No. 105 Squadron set the tone for these pinpoint raids when they attacked Nazi Gestapo headquarters in Oslo, Norway, on September 26, 1942. Four crews flew their Mosquito B. Mk. IV bombers a round-trip total of 1,770 kilometers (1,100 miles) and the mission lasted four hours and 45 minutes. A BBC news broadcast that followed this raid marked the first official confirmation that the Mosquito existed.

Like the bombers, de Havilland built sub-variants of the Mosquito adapted for day and night fighter operations. A Mosquito crew claimed the first air-to-air victory over a Dornier 217 twin-engine bomber on May 29, 1942. Many German fighters were also destroyed. From June 1944 to March 1945, Mosquitoes crews worked to defeat a menace hitherto unseen in warfare, mass attacks by low-flying, robot flying bombs propelled by pulse jet engines, the German V-1 'buzz bomb' vengeance weapons. In operations against shipping, Mosquitoes sank supply ships, and at least ten German U-boats along the French and Norwegian coasts. Mosquito crewmen flew many other unique missions including an unarmed, scheduled airline service between Scotland and Sweden. After the war, Mosquitoes laden with cameras surveyed all of India, Cambodia, and Australia. The last operational combat mission ended on December 21, 1955, when a Mosquito PR. 34A conducted a reconnaissance mission above suspected communist strongholds hidden in the jungles of Malaya.

During the war, the United States, South Africa, and the Soviet Union also operated Mosquitoes. After the war ended, Belgium, France, Turkey, Czechoslovakia, Yugoslavia, Norway, the Dominican Republic, and Israel flew the D. H. 98. Canada sold 200 Mosquitoes to Nationalist China in 1947. They were disassembled, shipped, and reassembled at Chinese factories.

Unarmed bomber. Internal load of four 500lb (227kg) bombs. First delivered to 105 Squadron at Swanton Morley in November 1941. First operational mission May 1942. Some aircraft were subsequently fitted with bulged bays for a 4,000 lb (1,814 kg) bomb (Highball Conversion).

Fighter-bomber and intruder. Armament of four 20mm Hispano cannon in fuselage 'under the floor' with 300 rounds apiece, plus four 0.303 Browning machine-guns in nose with 2,000 rounds apiece. With a load of two 250lb bombs in rear bay plus two 250lb (later 500 LB) bombs on wing racks - alternatively 50 or 100-gallon drop-tanks, mines, depth-charges or (under wings) eight x 60lb (5-inch) rockets. Some fitted with AI radar. Total production of this Mark was 2,584 - more than of any other version of the Mosquito.

Multi-role Coastal Command fighter bomber with low-blown engines. Armament of one 57mm six-pounder Molins gun with 25 rounds, four .303 Browning machine-guns and two 250lb (later 500 LB) bombs on wing racks - alternatively 50 or 100-gallon drop-tanks, mines, depth-charges or (under wings) eight x 60lb (5-inch) rockets. Some fitted with AI radar.. The Mk XVIII Mosquito was a rare variant as only 18, including the prototype were built. Most served with 248 Squadron and were in use until the end of the war. The exception was sent to the USA for evaluation and did not see front line service. What set all these aircraft apart was their Molins 6 pounder anti-tank gun.

The 57mm gun was produced by Molins Machine Co of Peterborough at the beginning of the war. It was intended to be mounted on small armored vehicles for use against tanks. It held 22 or 25 rounds in batches of 4 or 5 which were fed electrically to the breech. As one batch was fired the next was moved into position. It completed trials in 1942 but the Germans then introduced the Tiger tank which was impervious to 6 pounder shells.

The Hawker Hurricane IID's were fitted with 40mm Rolls Royce BF or Vickers Type S antitank guns but it was thought that something heavier was needed such as the Molins. As the Molins weighed 1,800lbs (816kg) this would mean a bigger, preferably twin engined, aircraft and de Havilland were approached to see if the Mosquito would do. As they had already done a feasibility study on the much heavier 3.7 inch (94mm) gun they agreed it was possible.

An old FBVI fuselage was used for static firing tests but a bolt broke so another method of attaching the gun had to be found. A new FBVI Mosquito, HJ732, was selected and modified to a Mk XVIII. The 12ft 5in (3.8 m) gun was mounted at a slightly downward angle and protruding 2 feet (600mm) from the nose. It now really looked like a Mosquito with a sting.

After further ground firing tests flying tests took place and a snag was found. If the Molins gun had a force of more than 2.5g imposed on it then it would not load the shells. Modifications were made so it was capable of sustaining both negative and positive g forces. However after firing 400 rounds the under surface of the flaps tore off. After strengthening of the flaps it was decided that only the two outer .303 Browning machine guns would be retained but with a greatly increased ammunition capacity.

Another minor problem was that the gun's breech was behind the crew and the spent shell cases were ejected inside the aircraft fuselage where they rolled about with aircraft movement. It was thought that if they were ejected externally they might hit the tailplane. To accommodate both the Molins and the Browning machine guns a different gunsight, the MkIIIa, replaced the MkII. This had different aiming marks for the Molins and the Brownings. In addition protective armor and long range fuel tanks were fitted so the aircraft could be used against U boats.

The aircraft served with 248 Squadron which was based at Predannack in Cornwall from October 1943. They proved to be a great success and the first U boat, U-123, was sunk on November 7 in the Bay of Biscay. The Molins armour piercing shell weighing 7.1lbs (3.2kg) were tipped with hardened steel and had no problems entering a submarine's pressure hull and creating great havoc inside. 248 Squadron protected Allied shipping during the D-Day landings and then was moved north to Banff in Scotland in 1944. From there it carried out many attacks on German shipping and installations in Norway.

Specification of the Molins 6 pounder Antitank Gun.

Bore 2.25in (57mm)
Action Recoil
Cyclic Rate 60 rounds per minute
Muzzle Velocity 2,600ft/sec (792m/sec)
Ammo feed Molins automatic
Magazine 22 rounds (some sources say 25)
Length 12ft 5in (3.8m)
Height 38in (965mm)
Weight 1,800lbs (816kg)

And why were they called the Tsetse Fly? Because they had a bigger bite than your normal Mosquito.

Considerably advanced bomber version. High-blown, two-stage engines. Bulged bay for 4,000 LB 1,814 kg) bomb or additional fuel. Much increased weight. Paddle-bladed propellers.

GB Planes and Specifications