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De Havilland DH 98 Mosquito



By 1937 Geoffrey de Ha-villand had become convinced that war with Hitler was inevitable. His idea had been a bomber fast enough to out fly ene-my fighters, a two-man crew, no rear armament, pure speed for defense. Two Rolls-Royce Merlins for power, and the sleek-est possible shape, entirely fashioned from wood, since in war there was likely to be a surplus of wood and woodworkers, DH thought, and a shortage of aluminum alloy. When he showed up at the Air Ministry with his drawings of a 400-mph gunless carpentry bomber faster than a Spitfire, they told him: "Forget it. You haven't built a war machine in years. Start on something simple, nothing this ambitious." As they drove home, DH and a colleague discussed the Mosquito and what a good idea it had been. As they turned in the factory gate at Hatfield, DH said: "We'll do it anyway."

DH set up to design and build his prototype plywood bomber in an old moated mansion, Salisbury Hall, five miles away. In December 1939, a team under Geoffrey de Havilland, with R E Bishop and C C Walker, started detailed design. The radiators for the Merlins were in a two-foot forward extension of the wing root between the engines and the fuselage, with intakes in the leading edge and cooling-air ex-its beneath the wings that actually gave cooling thrust, not drag. From these inboard radiators, and with a minimum of plumbing, they were also able to contrive a cabin-heat system that kept Mosquito crews warm at altitude. The fuselage was in cross section of tapered ovals. It was a balsa filling sandwiched between ply sheets, built in two vertical halves and glued together. The one-piece wing and fixed tail surfaces were wooden, but the control surfaces were ply-covered wooden flaps, metal-covered alloy ailerons and elevators, fabric-covered rudder. When all the wooden bits had been sanded smooth, screwed, glued and pinned, they were covered with fabric, the fabric stretched with dope and then painted.

The Rolls-Royce Merlin engines were descendants of the R-type racing engines developed for the Schneider Trophy floatplanes in the early 1930s. They were V-12s, cooled by a mixture of water and glycol, and (in later versions) aspirated by a two-stage, two-speed supercharger but the engines held power to rare altitudes. Takeoff power was 1,200 to 1,700 horsepower each, depending on the mark of Merlin.

The wing, while more straightforward than the fuselage, requires a great deal of jigging and tooling. Made in one piece 51 feet long, it contains two spars built up of booms of laminated spruce with webs of birch ply.

The rear spar is swept forward to give that distinctive wing shape. The spars are separated by 32 ribs, and then covered by an inner top skin of ply with an outer ply skin separated by spanwise douglas fir stringers. The bottom is single skin with stressed panels covering the fuel tank openings. All the skins are glued and screwed, with over 4000 screws in the top in alone.

The de Havilland team designed, drew up some 10,000 drawings, built a mockup, designed and built all the jigs and tooling, and rolled the aircraft out in 11 months.

On 1 March 1940 a contract was signed for 50 aircraft and the first flew on 25 November 1940, 11 months after design work began. The prototype was taken to Hatfield Aerodrome and assembled in November 1940. The prototype's first flight test pilot was DH's eldest son, also named Geoffrey de Havilland.

Conceived as an unarmed fast light bomber, the Mosquito was also planned as a photo-reconnaissance aircraft and a night fighter. The second aircraft, flown on 15 May 1941, was the night fighter prototype. Also constructed at Salisbury Hall, and young Geoffrey decided he'd fly it out of the pasture beyond the manor's cabbage patch, to save the time and labour of dismantling, trucking and reassembly at the airfield.

Test flying of the Mosquito revealed airspeed readings so high that DH wasn't sure he believed his pilots. So he one day "borrowed" (DH's word) a Spitfire as a pace aircraft. Both pilots agreed the Mosquito was almost 20 knots faster, doing eventually 370 knots at 30,000 feet. DH arranged demonstrations for the Air Ministry at which young Geoffrey would fly such unbomber-like manoeuvres as vertical rolls with one engine feathered.

In Boscombe Down trials the Mosquito proved some 20 mph faster than the then fastest mark of the Spitfire and was almost as manoeuvrable. It reached a maximum speed of 437 mph and a maximum altitude of 44,600 feet in the early 1940s.

The third prototype was a fighter variant.

Production wasn't helped by the extraordinary number of different models ordered - 43 in all - and by the Air Ministry oft changing its mind as to which variants were needed most urgently. Since they were possibly the fastest airplanes in the world for two and a half years, Mosquitos flew as fighters, both day and night, heavily armed with cannon and machine guns, as intruders-fighter-bombers, pure bombers, marker-bombers with the pathfinder squadrons of Bomber Command, photoreconnaissance aircraft, dual-control trainers, airliners, and as antisubmarine aircraft, carrying a six-pounder antitank gun or, later, rockets.

The first Mossies into service, in the autumn of 1941, were photorecon variants. The first PR aircraft made their initial daylight sorties over Paris on 20 September 1941. PR Mosquitoes also had the distinction of being the last in RAF frontline service, being withdrawn in December 1955. In time, these PRU aircraft roamed all over Germany and Europe. They flew between 22,000 and 30,000 feet, just below contrail height, so that any German fighters above them might be revealed by their own trails. But they'd photograph from as little as 400 feet if that was the cloud base. The Mosquitos' speed did give them substantial immunity from fighters - though not from flak - with the same FW-190s that the night-fighter Mosquitos were after being their principal adversary. When attacked by German jets, the Mosquitos could avoid their fire by tight turns; one held off two Me-262s for 15 minutes like this, till the Messerschmitts ran low on fuel. The Mosquitos' cameras were good enough to reveal the markings on German aircraft on the ground from 24,000 feet. By 1943, they were getting good photographs at night, using American photoflashes of 600,000 candlepower.




No.105 Squadron introduced Mosquitos into service in May 1942 as daylight bombers. Mosquitos were also the first Allied aircraft to bomb Berlin in broad daylight. The British learned that on January 30, 1943, both Goering and Goebbels were to address a rally in the city, and the RAF timed nuisance raids by two trios of Mosquitos to coincide with the start of their speeches. Back in Britain, those in the know tuned their wireless sets to Berlin radio, and to their great joy heard muffled noises and shouts, then an hour of martial music when there should have been live broadcasts of grandiose Nazi pomposity. No great damage was done, and one Mossie was lost; but Nazi pride had been ruffled, and Goering's boast that no Allied aircraft would ever bomb Berlin had been most obviously disproved.

Unarmed Mosquitos flew in BOAC colours between Scotland and Stockholm. The British needed Swedish ball bearings, and they also transported POW mail and a few VIP passengers in a makeshift bunk inside the bomb bay. Passengers were loaned a flying suit, warm boots, Mae West and parachute for the trip; they had oxygen masks, heat and an intercom to the pilot but no means at all of seeing out.

The Mosquito was an economical weapon. Four or five could be built for the man-hours necessary for one heavy bomber; wood and women were resources not in short supply and women did much of the work in building Mosquitos. There were only two crewmen to train, against 10 for a heavy; two engines against four, and half the fuel con-sumption. By the war's end, Mosquitos were carrying 4,000-pound bombs to Berlin: about the same load as a B-17, but the Mossies only took half the time and had a third of the loss rate.
A total of 466 Mosquito Night Fighter Mk IIs were produced.

The T.Mk.IIIs were a direct development of the F.Mk II fighter, possessing dual controls and no armament.

The origin of the armed Mosquito T.Mk.IIIs was wartime Australia. The need for training in the ground attack role had led to some British-built T.Mk.III trainers being armed with the machine gun packs removed from FB.Mk.40s previously converted to the photo reconnaissance role.


Mosquito B.IV


The prototype of the most widely used of the Mosquito fighters (HJ 662) made its first flight in February 1943, and more than 2,500 of this Mk VI version were built eventually. With two 1,710 hp Rolls-Royce Merlin XXX engines, it had a maximum level speed of 407 mph (655 km/h) at 28,000 ft (8,535 m).




The B.IV Srs 2 bomber version first operation was on 20 November 1942.


Mosquito FB.26 KA114


The Royal Navy operated a number of Mosquito FB.Mk VI and T.Mk 3 land-based aircraft in the anti-ship attack and trainer roles, but its most important type was the Sea Mosquito TR.Mk 33 carrierbome torpedo and reconnaissance fighter. This model first flew in November 1945 and entered service in August 1946. The variant was based on the FB.Mk VI with larger propellers, American radar, and naval features such as folding wings and an arrester hook. With the Second World War over, deliveries of this model totalled just 50, though there were also six examples of the related Sea Mosquito TR.Mk 37.

The availability of two-stage two-speed supercharged versions of the Merlin led to the introduction of numerous new Mosquito bomber and PR versions but, apart from their use in the high-altitude NF Mk XVs, these engines were not introduced in a fighter variant until the spring of 1944, when the Mosquito NF Mk 30 appeared. This night fighter had the same “universal” radome as the NF Mk X1X, together with 1,680 hp Merlin 72 engines (in the first 70 production examples) or 1,710 hp Merlin 76s (in the other 460 built). First Mk 30 flew in March 1944 and operational service began in June 1944 with No 219 Squadron for home defence, other squadrons using this type for long-range escort of Bomber Command formations attacking Germany in 1944/45.


Mosquito night fighters


The PR.34 differences from earlier machines appear in an altered canopy, that has an astrodome in addition to the bulged side windows and vee-windscreen found on the bomber version. The engine cowlings feature an enlarged chin intake and the fuselage belly has a distinct bulge. The aircraft also features the paddle-bladed propellers that give the late series of this type such an air of purpose.

On 12 March 1945 the last bomber variant of the Mosquito, the B35, made its first test flight. The war had ended before it could be used operationally, but it entered service with the post-war Royal Air Force and served as a bomber until the beginning of 1954.


Some Mosquito B35s were converted for other duties including target-towing and in this role they continued in service until 1963.

The Mosquito NF Mk 36 was similar but had 1,690 hp Merlin 113s; the first example flew in May 1945 and 163 were delivered, up to March 1947. The Force Aérienne Beige acquired sufficient to equip two squadrons after RAF service, these remaining in service until the mid ‘fifties. The final fighter version of the Mosquito was the NF Mk 38, differing from the Mk 36 in having British Al Mk X1 radar in place of American Al Mk X and Merlin 113 / 114 engines, Of 101 built, 54 were supplied to the Yugoslav Air Force in 1950 and the others were scrapped.

The Mosquito T.43 is an Australian-built dual control model similar to the T.3 but with Packard Merlin engines and retaining its armament of four .303 machine guns and four 20mm cannon.

Other versions were Sea Mosquito TR.Mk 33 (initial model with American ASH surface search radar), Sea Mosquito TR.Mk 37 (derived model with British ASV surface search radar), and Mosquito TT.Mk 39 (naval target-tug model based on the B.Mk XVI bomber).

Towards the end of the war Mosquito units were averaging one aircraft loss per 2,000 sorties - by far the lowest figure recorded by Bomber Command. Mosquito bombers, which had entered service carrying a 907kg bomb load, were later to carry a 1800kg block-buster in a bulged bomb bay. Mosquito fighters were to distinguish themselves in fighter-bomber, anti-shipping and night-fighter roles, and were to destroy some 600 V-1 flying-bombs in the defence of Britain. For reconnaissance duties the Mosquito was the RAF's major long-range aircraft in this category, serving in Europe, Burma and the South Pacific. Including 1,342 Mosquitoes built in Australia and Canada, total construction was 7,785 aircraft when production ended in November 1950. 6,710 were built during WW2.


Eighty-nine were ordered by the RNZAF to re-equip 1946-55 but the bulk were never put into service.




Specification F.18/40 was originally written for a fixed gun two-seat night fighter to replace the BP Defiant, dated 10/11/1940, but on 9 December a correction was made in that armament was changed to incorporate a 'dorsal power-operated turret'.

de Havilland was asked to examine the spec, even though the firm was not invited to tender to it. The result was the two turret fighter Mosquitoes, the fourth prototype W4053 built at Salisbury Hall and flown from there to Hatfield with the turret fitted on 14 September 1941, and W4073, first flight 5 December from Hatfield.
turret equipped Mosquito
The turret was to be a Bristol B.11 four-gun turret, which was designed for the Bristol Beaumont bomber project, and was very light and compact.
DH also did much research into Mosquitos fitted with turrets as a result, to discover that a considerable amount of performance was lost as a result of the installation. The two turret fighter Mosquitos, after having their turrets removed, went on to become the prototype T.III trainers.
turret equipped Mosquito
W4050 July 1941
The prototype W4050 was fitted with a mock up turret for aerodynamics trials in July 1941. In September 1941 the fourth prototype Mosquito, W4053, which was the first prototype turret fighter (the third prototype, W4052 was the first night fighter NF.II, built to F.21/40), flew for the first time, but with a mock up turret only.
By then the decision had been made not to continue with the turret fighter, although a second prototype turret fighter was finished, W4073, in December 1941. This aircraft and W4053 became the prototypes of the T.III trainer variant once the turret fighter was cancelled.

This faint vertical line on the canopy of the prototype shows where the fairing for the turret mock up rubbed against the canopy. Within the structure are four mounting bolts where the turret was fitted.


Reconstruction Répliques Avions Anciens Mosquito .75




Engines: 2 x 1,680 hp Rolls‑Royce Merlin 72.
Length 41.5 ft. (12.65 m.).
Wing span 54.2 ft. (16.5 m.)
Weight empty 15,510 lb. (7,035 kg.)
Crew: 2.
Max. bomb load: 4,000 lb. (1,800 kg.)
Max speed 408 mph (656 kph)
Ceiling 37,000 ft. (11,000 m) fully loaded
Range 1,370 miles (2,200 km.)
Stall flaps down and light: 90 knots, 119 knots flaps up and at gross weight
Vmc: 185 knots at full power and 175 knots at climb power.
Wingspan: 52 ft 6 in
Unarmed reconnaissance
Wingspan: 54 ft 2 in
Night fighter
Engines: 2 x Rolls-Royce Merlin 21, 1230 hp
Seats: 2 side-by-side
Armament: 4 x 20mm Hispano cannon 300 rds / 4 x 0.303 Browning 2000 rds each
Dual control trainer
First flown January 1942
Last delivery 1949
Engines: 2 x Rolls-Royce Merlin 21, 1230 hp
Unarmed bomber
Engines: 2 x Rolls-Royce Merlin 21, 1230 hp
Bombload: 4 x 500 lb / 227 kg
Later bulged bomb-bay: 4000 lb / 1814 kg
Mosquito FB Mk VI
Engine: 2 x Rolls-Royce Merlin 25, 1208kW / 1,635 hp
Props: 12 ft 0 in (3.66 m) dia 3‑blade.
Max take-off weight: 10115 kg / 22300 lb
Empty weight: 6486 kg / 14299 lb
Wingspan: 16.51 m / 54 ft 2 in
Length: 12.47 m / 40 ft 11 in
Height: 4.65 m / 15 ft 3 in
Wing area: 42.18 sq.m / 454.02 sq ft
Wing loading: 47.15 lb/sq.ft / 230.0 kg/sq.m
Max. speed: 583 km/h / 362 mph at 13,000 ft (3,960 m)
Cruise speed: 523 km/h / 325 mph
Service Ceiling: 10060 m / 33000 ft
Initial climb rate: 2500.00 ft/min / 12.70 m/s
Range: 2655 km / 1650 miles
Endurance: 7 hr
Armament: 4 x 20mm Hispano cannon, 4 x 7.7mm Browning machine guns
Bomb load: 4 x 250 lb / 113 kg – later 2 x 250 lb / 113 kg & 2 x 500 lb (2,000 lb / 900kg)
Crew: 2
No built: 2584
Engine: 2 x Rolls‑Royce Merlin XXX, 1,710 hp.
Max level speed of 407 mph (655 km/h) at 28,000 ft (8,535 m).
Wing span: 54 ft 2 in (16.51 m).
Length: 40 ft 6 in (12.34 m).
Height: 15 ft 3 in (3.51 m).
Max TO wt: 22,300 lb (10,115 kg)
Canadian-built – used in North America only
Engines: 2 x Rolls-Royce Merlin 61
Engines: 2 x Rolls-Royce Merlin 72, 1680 hp
Bombload: 4000 lb
Reconnaissance - First flew July 1943
Engines: 2 x Rolls-Royce Merlin 72, 1680 hp
Night fighter F.II with AI Mk.VIII radar
Engines: 2 x Rolls-Royce Merlin 21, 1230 hp
Seats: 2 side-by-side
Armament: 4 x 20mm Hispano cannon 300 rds
As Mk.XII but new build Aug 1943
Mk.VI wing
High altitude pressurised fighter
Wing span: 59 ft
Radar: AI Mk.VIII
pressurised cockpit
Engines: 2 x Rolls-Royce Merlin 72, 1680 hp or Merlin 74 or 77, 1710 hp
Armament: 4 x 0.303 Browning mg
Bombload: 4000 lb
Radar: AI Mk.X or SCR 720
Armament: 4 x 20mm, 500 rds each
Role: Fighter-bomber
Wingspan: 54 ft 2 in
Length: 40 ft 10.75 in
Max speed: 380 mph at 13,000 ft
Range: 1270 miles
Armament: 1 x 57mm Molins gun, 4 x .303 in Bowning mg
Bombload: 2 x 500 lb bomb
Coastal Command fighter
Armament: 1 x 57mm 6-pounder Molins, 24 rds / 4 x .303 Bowning mg
Bombload: 8 x 60 lb rockets or bombs
Engines: 2 x Rolls-Royce Merlin 25, 1640 hp
Radar: AI Mk.VIII or SCR 720
Canadian-built B.IV
USAAF designation F-8
Engines: 2 x Packard V-1640 Merlin
Engines: 2 x Packard V-1640 Merlin
Engines: 2 x Rolls-Royce Merlin 76, 1710 hp
NF Mk 30
Based on Mk.XIX
Max speed, 338 mph (544 km h) at sea level and 424 mph (682 kmh) at 26,500 ft (8077 m)
Initial climb, 2,250 ft/min (11,4 m/sec)
Range, 1,180 mls (1 900 km)
Empty weight, 15,156 lb (6880 kg)
Loaded weight. 21,600 lb (9806kg)
Span, 54 ft 2 in (16,51 m)
Length, 41 ft 6 in (12,64 m)
Height, 15 ft 3 in (4,65 m)
Wing area, 450 sq ft (41,81 sq.m).
Engines: 2 x Rolls-Royce Merlin 25, 1640 hp
Extended-span reconnaissance
Engines: 2 x Rolls-Royce Merlin 113/114, 1690 hp
Sea Mosquito TR.Mk 33
1st RN Sea Mosquito
Folding wings
Engines: two 1,640-hp (1,223-kW) Rolls-Royce Merlin
Prop: 4 blade
Maximum speed 385 mph (620 kph) at 13,500 ft (4,115 m)
Initial climb rate 3,000 ft (914 m) per minute
Service ceiling 30,000 ft (9,145 m)
Range 1,260 miles (2,028 km)
Empty weight: 17,165 lb (7,786 kg)
Normal take­off 22,500 lb (10,206 kg)
Wing span 54 ft 2 in (16.51 m)
Length 42 ft 3 in (12.88 m)
Height 13 ft 6 in (4.11 m)
Wing area 454.0 sq ft (42.18 sq.m)
Armament: four 20-mm cannon, 2,000 lb (907 kg) bombs or one 18-in (457-mm) torpedo.
Radar: ASH
Equipment: arrestor hook, JATO boost
Strategic reconnaissance
Pressurised cabin
Engines: 2 x Rolls-Royce Merlin 113/114, 1690 hp
Fuel capacity: 1269 Gal (200 gal drop tanks)
MK. 35
Engines: 2 x Rolls-Royce Merlin 113/114, 1690 hp
Engines: 2 x Rolls-Royce Merlin 113/114, 1690 hp
Wingspan: 54 ft 2 in / 16.52 m
Length: 44 ft 6 in / 13.57 m
Max speed: 404 mph / 646 kph
Armament: 4 x .303 Browning MG, 4 x 20 mm Hispano cannon
Crew: 2
Radar: AI Mk.X
Torpedo fighter
Engines: 2 x Rolls-Royce Merlin 113/114, 1690 hp
Radar: AI Mk.IX
General Aircraft rebuilt target tug
Australian built Mk.VI
FB.40 conversions
Australian-built Mk.IX & Mk.40 derivatives
Australian trainer
Engines: Packard Merlin








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