de Havilland DH.98 Mosquito
Multirole Heavy Fighter / Fighter-Bomber Aircraft
The classic twin-engine British de Havilland DH.98 Mosquito night fighter found few challengers during World War 2.
Authored By: Staff Writer | Last Edited:
Discussions of war-winning World War 2 aircraft regularly seem to leave out one of the most famous and successful of the conflict - Geoffrey de Havilland's twin-seat, twin-engined DH.98 "Mosquito". The type was a true "multirole" performer in that in was used as a fighter, fighter-bomber, reconnaissance mount, night fighter, anti-ship platform, patrol, intruder and interceptor against the best the Reich could offer - very few Axis aircraft could even catch it. The aircraft was designed from the outset as a multirole weapon and served throughout most of World War 2 and into the Cold War years before finally being retired. Her crews enjoyed her basic creature comforts (heated cockpit), fighter-like performance, handling, and speed and inherent offensive capabilities (cannon, machine gun, bombs, torpedoes and rockets), making her a star in the history's greatest air war. The DH.98 earned the nickname of "Wooden Wonder" in reference to its heavy use of wood throughout her design.
Origins of the DH.98 was owed to development of all-wood de Havilland racing planes appearing in the mid-1930s as the designation of DH.88 "Comet". The extensive use of a wood (plywood/balsa) with stressed skin approach proved them somewhat of a revolutionary departure from the metal-skinned airframes beginning to take hold in military inventories around the globe. The Comet went on to claim the London-Melbourne Centenary Races and de Havilland then moved to produce an airliner-minded design utilizing the same wood approach, this giving rise to seven examples of the beautifully streamlined DH.91 Albatross first flying in 1937. Despite his wooden designs being consistently rejected by the British Air Ministry, de Havilland persisted when authorities sought a new medium bomber design through Specification P.13/36. However, once again, a modified form of the Albatross was rejected by the Air Council due to the focus falling on metal-skinned designs.
The Mosquito Takes Shape
Undeterred, de Havilland has his design team working on an all-new wooden concept as a private venture, an unarmed light bomber that would include a two-man crew in a smaller fuselage frame powered by two outboard engines and feature an internal bomb bay. The design was a true departure from the metal-encased, lumbering machine-gun-defended mounts the Air Ministry sought. De Havilland's design held many strong inherent qualities - it was dimensionally smaller and lightweight thanks to the wood construction and lack of complicated and heavy defensive turrets or gun stations. This also helped reduce a crew of six or eight men to just two - a pilot and navigator. The de Havilland design was also intended to fly higher than enemy air defenses could reach and faster than any intercepting enemy aircraft could hope to manage. The aircraft's layout was consistently de Havilland, a well-formed teardrop shape with the two-man cockpit fitted in the extreme forward portion of the fuselage, engines mounted in streamlined nacelles to either side of the cockpit and wings mid-mounted monoplane assemblies. The empennage was highly conventional for the period consisting of a single vertical tail fin and low-set horizontal tailplanes. The pilot and his navigator sat in a side-by-side arrangement.
With Germany on the move across both political and military fronts by 1939, much thought on the part of the British was in stemming the tide with the weapons and manpower available. As such, little interest remained for the de Havilland concept. It was with some help from de Havilland's World War 1 ally - Air Marshal Sir Wildred Freeman - who sat on the Air Council that the new de Havilland approach was greenlighted for development in December of 1939. The RAF contracted for a bomber prototype and 50 aircraft were slated for purchase to Specification B.1/40.
Inside the Mosquito
Internally, the pilot and navigator sat in a side-by-side formation, the pilot on the left with the navigator to the right. Entry/exit to the aircraft was through a hatch along the navigator's right. The cockpit was relatively well organized with throttle and engine gauges set along the left hand side within easy reach. Basic dials were spread about the uncluttered instrument panel which DH-98 pilots regarded as good to excellent. A small passageway along the right of the instrument panel allowed crew access to the nose which, in non-solid-nosed versions, featured a clear plastic windscreen for bombing. The cockpit was heated for high-altitude flying and generally regarded as more comfortable than the Bristol Beaufighter it replaced. Other production versions introduced cockpit pressurization for extreme high-altitude work.
Three Basic Forms
Developed in complete secrecy, the de Havilland endeavor was given the designation of DH.98 "Mosquito" and her powerplant of choice became the excellent Merlin series that also powered the famous Supermarine Spitfire fighters. The de Havilland wood technique was slightly modified for the Mosquito as the aircraft would have to be reinforced for the abuses of military combat. Development eventually went beyond the original bomber prototype (FB) and included a specialized photographic reconnaissance (PR) version as well as a dedicated night fighter (NF) variant along with basic fighter variations (F). Each type exhibited their own developmental "marks" followed by a number to signify key changes between each design.
Wood Over Metal
The principle use of wood was key to the success of the Mosquito, especially concerning its war time production. Metals proved a sought-after resource and, with it, those specialists that could work with such materials to help form the hulls of battleships and submarines, the airframes of modern aircraft or the shells of bombs. The Mosquito therefore, would rely on the readily available supplies of wood through the British Empire and essentially require the skilled services of woodworkers who were not as critical to the primary British war effort. Such a revolutionary, forward-thinking approach partially made the successes of the Mosquito design possible (her crews being the other part).
Mosquitoes were generally armed with 4 x 7.7mm Browning machine guns in the nose with 4 x 20mm Hispano cannons under the cockpit floor. Some versions did away with the machine guns altogether while other forms replaced the 4 x cannons with a single 57mm cannon. The internal bomb bay supported up to 500lb of ordnance in original versions and this later ballooned to bomb load outs comparable to that of American B-17s. Bombs could also be added to hardpoints under each wing - initially 2 x 250lb types then 2 x 500lb types. Additionally, the Mosquito was eventually tested and cleared to fire underwing rockets. Navalized Mosquitoes were outfitted with a single torpedo under the fuselage. External fuel tanks ultimately worked they way into the DH.98's load out and offered extended ranges.
The Mosquito in Practice
The prototype Mosquito first took to the air on November 25th, 1940 and any remaining Air Ministry skeptics were immediately silenced for good. The DH.98 proved a thoroughbred in the air and only required slight modifications to flush out teething issues before serial production was set to begin. A fighter prototype was unveiled in May of 1941 and the DH.98 as a whole was formally introduced for service with the RAF that same year. The photographic reconnaissance variant was outfitted with three camera systems with an optional fourth (1 x F.52 20- or 30-inch daytime camera, K.17 6-inch survey and mapping camera and 1 or 2 x F.24 cameras). The night fighter variant was quickly ushered along and given sophisticated Airborne Interception (AI) radar for the task. The type also retained the 4 x 20mm cannon array while later versions dropped the 4 x machine guns. A bulletproof windscreen was added for crew protection and wing spars were reinforced for improved fighter-like qualities.
One of the key detriments to early Mosquito successes was in a limited production rate which, in turn, limited availability of the excellent aircraft for British flight groups. Mosquitoes were accepted into Fighter Command ranks in January of 1942 and were used to replace outmoded types such as Bristol Beaufighters as quantities allowed. The first combat-level sortie involving a Mosquito was on September 17th, 1941 when a photographic reconnaissance mount of No. 1 PRU was sent over the border between France and Spain. Night-fighting Mosquitoes proved the design supremely sound when, in the span of a few months in early 1943, pilots scored kills against no fewer than 17 enemies. The success of the fighter-bomber, reconnaissance and night fighter types did away with the planned dedicated fighter prototype in time - thusly leaving only three prototypes making up the family line which numbered over 7,000 examples.
Success for the DH.98 was not limited solely to its night-fighter forms for the aircraft also excelled in daytime sorties against all manner of enemy targets - be they in the air or on the ground. Reconnaissance versions could outpace most intercepting German fighters while intruding sorties numbering a few aircraft could be used for surprise raids against unsuspecting strategic positions. Mosquitoes could utilize their combination machine gun/cannon fire to strafe ground targets such as depots, supply trains, troop columns and airfields. Others went into battle with internal and external bomb loads for tactical bombing forays deep within enemy territory, on approached sometimes no higher than at treetop level. Still others were eventually outfitted with rockets and launched against enemy shipping where their rockets could be used to devastating effect against unsuspecting Axis vessels and submarines. A few forms even gave up their 4 x cannons for a single 57mm cannon to be used exclusively against enemy shipping in the ship-busting role - such was the flexibility of the airframe. Mosquitoes were also used by Bomber Command to "light the way" for accompanying heavy bombers in British night time raids through use of the "Oboe" target-marking facility - one of the more effective systems deployed during "blind bombing" in all of the war.
Night fighter forms were generally progressed by the evolution of better radar suites. Later forms saw their machine gun armament removed as the 4 x cannons proved equally effective on their own (this also proved a weight-saving measure). Crews operating in the thick of night relying heavily on their onboard technology to bring an enemy aircraft within range under complete surprise. The Mosquito's impressive 4 x cannon battery could bring down an enemy bomber in a few short, well-placed bursts at range. In time, a rear warning radar was also installed which furthered the capabilities of the night-fighting DH-98 crews by detecting pursuing enemy aircraft.
Mosquitoes were used as a psychological tool as well, targeting housing for factory workers and their families. In this role, bombing raids disrupted any night of fine sleep, resulting in a weary and battered workforce the following day - air raids were specifically set up to coincide within two hours prior to a work shift. It was not until September of 1942 that Mosquitoes were finally granted a shot at bombing Berlin proper in a daring daylight raid. Also in September, Mosquitoes bombed - with marginal success - the Gestapo HQ in Oslo covering some 1,100 miles total - to date, the longest Mosquito flight of the war.
Only three prototypes of the DH.98 were ultimately completed, each used to solidify the expected fighter-bomber, fighter/night fighter and reconnaissance forms. They were assigned the serial numbers of W4050, W4052 and W4051 respectively.
Mosquito Photographic Reconnaissance Variants
Reconnaissance marks began with the PR.Mk I of which ten were delivered. These were followed by the PR.Mk IV which were born as conversions from existing B.Mk IV bombers and equipped with four cameras. Five more conversions became the PR.Mk VIII with two-stage, two-speed supercharged Merlin 61 series engines of 1,565 horsepower for higher altitude function. The PR.Mk IX then followed in 90 examples based on the B.Mk IX with Merlin 72/73/76/77 series engines of 1,680 horsepower and increased fuel capacity and, thusly, increased operational ranges. The PR.Mk XVI introduced a pressurized cockpit for high-altitude service and was outfitted with three external fuel tanks for increased range. The PR Mk 32 was similar in scope and intended for high-altitude, long endurance reconnaissance with Merlin 113/114 engines of 1,960 horsepower and based on the NF.Mk XV night fighter. Final reconnaissance versions arrived as the PR.Mk 34 and the PR Mk 34A which lacked cockpit and fuel tank armoring but brought about increased ranges through a bulged fuselage design. The PR.Mk 35 was based on the definitive bomber form described in the next paragraph (B.Mk 35). The PR.Mk 40 was the Australian reconnaissance development of the FB.Mk 40 fighter bomber. The PR.Mk 41 was, therefore, a further development of the Aussie PR.Mk 40 though with two-stage engines.
The initial fighter-bomber (FB) Mosquito form became the FB.Mk VI and this variant was powered by 2 x Merlin 21/25 of 1,460 and 1,635 horsepower respectively. The Mk VI proved the definitive fighter form and used in the day/night "intruder" raiding role. Their airframe supported internal bombs as well as underwing hardpoints for bombs, rockets and external fuel tanks. The nose-mounted machine gun armament (4 x 7.7mm) and underfuselage cannon armament (4 x 20mm) were both retained for the offensive role. These were followed by the FB.Mk XVIII which numbered 45 and featured a single 57mm autocannon for ship-busting sorties and additional armor protection at low combat altitudes with wing support for launching rockets. FB.Mk 26 (Packard Merlin engines) and FB.Mk 40 were both produced in Canadian factories and proved similar to the original FB.Mk VI. The FB.Mk 40 fighter-bomber was the basis for the Australian PR.Mk 40 mentioned previously.
Mosquito Dedicated Bombers
The first Mosquito bomber sortie was a an armed sortie charged with photographing the aftermath of a recent 1,000-strong Allied bomber raid over Cologne following May 30th - the aircraft sent in with bombs to attack any remaining targets of opportunity. The initial Mosquito bomber version was the B.Mk IV Series 1 of which ten were converted from PR forms. These were followed by 273 examples of the B.Mk IV which carried up to 500lb of ordnance in the internal bay and 2 x 250lb bombs underwing. 245 examples of the B.Mk XX were produced in Canada following the B.Mk IV specification and powered by Merlin 31/33 engines. The B.Mk V was a pressurized high-altitude variant with Merlin 21 powerplants. The B.Mk VII was a Canadian-produced mark with Merlin 31 series engines and 25 were produced (the USAAF taking on six) and underwing hardpoints. Fifty-four examples of the B.Mk IX high-altitude version were produced with Merlin 72/73/76/77 engines with support for the 4,000lb "Cookie / Dangerous Dustbin" blockbuster bomb. The B.Mk XVI was a high-altitude pressurized version of the B.Mk IX. The final bomber variant became the B.Mk 35 outfitted with Merlin 113/114A engines. By now, the airframe could carry up to 4,000lb of ordnance and reach speeds of over 400 miles per hour and altitudes nearing 40,000 feet. Surplus airframes served in the target tug role (as T.Mk 35) and as ultra-fast, high-flying photographic reconnaissance mounts (PR.Mk 35).
Mostuito Night Fighters
There proved a bevy of night fighter forms developed by the British from the base DH.98 design. These began with the NF.Mk II of which a total of 466 were produced and were broadly based on the F.Mk II fighter. Slightly modified versions emerged as the NF.Mk II (Special) which saw their radars removed for extra fuel storage and improved ranges. The NF.Mk VI fitted bombs and underwing rockets. The NF. Mk XII fitted AI Mk VIII radar and 270 examples were produced. The NF.Mk XV were four examples of converted F.Mk XV mounts with AI Mk VIII series radar and relocated machine gun nose armament (to a fuselage gunpack) intended for high-altitude interception. The NF.Mk XVII was born from 99 examples of NF.Mk II mounts converted with American SCR-720 (British AI.Mk X) series radar and Merlin 21/22/23 engines. The NF.Mk XIX were improved NF.Mk XIII forms for support for either radar (American or British) installation to which 220 examples appeared. The NF.Mk 30 became the last war-time Mosquito variant and fitted Merlin 76 two-stage engines of 1,710 horsepower for high-altitude work to which 526 examples of the type were produced in all. The Mk 30 proved the definitive night fighter example of World War 2 and assisted British bomber formations during their night time raids over Germany and elsewhere. The NF.Mk 36 was a high-altitude post-war variant with American radar and Merlin 113/114 engines, seeing 266 examples produced. Similarly, the NF.Mk 38 was another post-war model with British radar and 101 examples delivered. The NF. Mk 36 deserves special mention here as being the only all-weather fighter in service with the RAF until 1951 to which the type was finally succeeded by new jet-powered night fighters. Likewise, the NF.Mk 38 deserves its own special mention as the final Mosquito mark produced, this in November of 1950 out of the Chester facility.
Several Mosquito airframes were converted to serve as dedicated torpedo-bomber aircraft that began with the TR.Mk 33 "Sea Mosquito" prototype. The prototype was the first British twin-engine aircraft landed on a British carrier (March 1944 on the deck of the HMS Indefatigable). Such aircraft were completed with four-bladed propellers, a revised and reinforced undercarriage, bulbous covered radome (housing an AN/APS-6 system) and an arrestor hook for carrier based landings. Additionally, wings were hinged to fold for a smaller footprint aboard space-strapped British carriers of the period.TR marks were powered by Merlin 25 series engines and armed through 4 x 20mm cannon and up to 500lb of internal ordnance with optional support for external rockets and an externally-mounted torpedo. 50 TR.mk 33 aircraft were produced. The TR.Mk 37 then followed and was differentiated by its use of the ASV Mk XIII radar suite. Sea Mosquitoes were not available in useful numbers until 1946, World War 2 having concluded in 1945.
Several other lesser-storied versions of the Mosquito were inevitably produced. This included dedicated trainer mounts in the T.Mk III, T.Mk 22 (Canadian equivalent of the T.Mk III), T.Mk 27 (T.Mk 22 with Packard Merlin engines), T.Mk 29 (FB.mk 26 conversions) and T.Mk 43 (Aussie version of the T.Mk III). Target tugs were the TT.Mk 35 and TT.mk 39.
Production of Mosquitoes ranged beyond English factories for Canadian and Australian lines also contributed. Talks with setting up American lines fell to naught. Canadian production amounted to 1,133 examples available in ten marks ranging from the mentioned British bombers, fighter-bomber and trainer forms. Australian marks numbered six and included a photographic reconnaissance mount, several fighter-bomber forms and a trainer variant. In all, eight notable producers took part in manufacturing of various Mosquito marks, the primary supplier becoming de Havilland of Hatfield. A total of 7,781 Mosquitoes were built throughout the war and into the ensuing Cold War years, production spanning from 1940 to 1950. Operators proved numerous and included Australia, Belgium, Burma, Canada, China, Czechoslovakia, Dominican Republic, France, Israel, New Zealand, Norway, Poland, South Africa, the Soviet Union (Lend-Lease), Sweden, Turkey, Switzerland, the United Kingdom, the United States (limited) and Yugoslavia. Many became post-war operators.
V-1 Rocket Hunters
The DH.98 Mosquito was also one of the few wartime aircraft that could match the speed of incoming German V-1 rockets being launched from enemy-held territories across northern Europe. Such terror weapons accounted for the deaths of 30,000 British citizens during the war - the V-1 and subsequent V-2 rockets proving nothing more than a last-ditch effort on the part of the collapsing German war fronts. The DH.98 could utilize its speed to intercept such weapons and destroy them with relative ease only assured by a steady hand at the controls. In this role, from June 1944 onwards, Mosquitoes accounted for 428 V-1 rockets intercepted. Mosquitoes joined other Allied aircraft in hunting and destroying V-rocket launch sites throughout the Third Reich.
The DH.98 endured in post war service, entering the inventories of many foreign air forces. Mosquitoes (FB.Mk IV) were used in anger over Java against Indonesian extremists which marked some of the last combat sorties of the fine aircraft. The RAF retired their final Mosquito fighters in 1950.