The start of it all – W4050, the Mosquito prototype

Some of the most important aircraft of the Second World War never saw combat, had quite a few faults, and sometimes had a flying life which was measured in weeks or even days. I’m talking about the prototypes; these machines which were, in some cases, little more than partially equipped, unarmed test rigs which bore only a passing resemblance to the aircraft with which the squadrons would eventually be equipped. The Allies usually managed with a handful of test examples, sometimes only one or two per type; the Germans, however, had a history of producing large numbers of ‘Versuchs’, or test examples, for each new aircraft. The Fw190, for example, had no less than 80 ‘V’ aircraft built during the lifetime of this classic German fighter.

Prototypes tend NOT to survive, in wartime especially. Technology, during the Second World War, moved at a frantic pace, and once their test programme was over, if there were no other modifications to consider, the prototype was usually pushed unceremoniously into the corner of a hangar and later just scrapped. This was because of their ‘one off, hand built’ status, making them not easily brought up to any ‘build standard’, and sometimes the punishing nature of their testing program. Occasionally, a prototype was retained for a period, as it might be needed to fly some pieces of new equipment or a different armament fit. Despite the fact that both the prototypes of the incredibly significant Hawker Hurricane (K5083, first flight 6th November, 1935) and the Supermarine Spitfire (K5054, first flight 5th March, 1936) flew before WW2 broke out, neither of them survived the war. Imagine the delight, therefore, of all aviation enthusiasts to be able to visit the de Havilland Aircraft Heritage Centre (incorporating the Mosquito Museum) at London Colney and see W4050, the actual Mosquito prototype which began a great aviation dynasty.

In 1938, Geoffrey de Havilland had thought of an unarmed bomber which, by its great speed, would be able to out-run fighters and deliver a ‘worthwhile’ bombload as far as Berlin (even at this stage, it was assumed that war would eventually break out, and that Germany would once again be the enemy). At first he thought of a reduced scale DH Albatross, powered by two R/R Merlins, but in October, 1938 the Air Ministry turned de Havilland’s down. Undaunted, de Havilland went back to work, lobbying whoever would listen inside the Ministry. It so happened that he had a champion; Air Chief Marshal Sir Wilfrid Rhodes Freeman, 1st Baronet, GCB, DSO, MC, RAF, the Member for Development and Production on the Air Council (the highest governing body of the RAF) was an ardent believer in what de Havilland was trying to do, and eventually, on December 29, 1939, the company was given the green light to design a ‘light bomber’ (with potential for future photo reconnaissance or fighter use). A design team, under Ronald Eric Bishop CBE FRAeS,the company’s Chief Designer, was quickly set up at the 17th century mansion of Salisbury Hall, near London Colney, well away from any prying eyes. On March 1st, 1940, still in the period of the so-called Phoney War in France and Belgium, de Havillands were given a contract for 50 aircraft, to Specification B.1/40, to be built provided they did not interfere with the company’s other war work, such as producing Tiger Moth trainers! Sir Wilfred Freeman had fought so hard for the unarmed aircraft that it was known inside the Air Ministry as ‘Freeman’s Folly’; the aircraft had many detractors, at this stage.

As the Western Front erupted in flames, and Hitler’s Blitzkrieg swept all before it, there became little time to develop new aircraft, and every aircraft company was ordered to concentrate on either building or repairing a very limited number of existing types, including the Spitfire and the Hurricane. It so happened that de Havilland’s had a contract to build Merlin engines under license from Rolls-Royce as well as repair damaged Hurricanes, and the new bomber came close to being cancelled on several occasions. It was only because the aircraft used so little in terms of strategic materials such as aluminium, that work on it was allowed to continue.

Gradually, W4050 took shape, in a small hangar, disguised as a barn, on the other side of the moat at Salisbury Hall. It was an elegant two-seater, with the navigator sitting slightly behind and to the left of the pilot. The fuselage was made of a lightweight plywood/balsa/plywood ‘sandwich’ which was formed over two mahogany moulds, liberally coated with glue (initially a casein-based adhesive, made from milk proteins) then ‘cured’ by the application of pressure and heat. The wing was built in one piece, with a laminated spar of Canadian Yellow Spruce, and skinned with birch ply. Two Rolls-Royce RM.3SM Merlins of 1,298hp were fitted, driving three-bladed constant-speed propellers.

The great moment came on 25th November, 1940, when the prototype was wheeled out, painted all-over Trainer Yellow, with black spinners, and carrying the second class Registration Mark of E0234. Geoffrey de Havilland Jnr. and John Walker, the Chief Engine Installation Designer, took off from the company airfield on the very first proving flight. All went relatively smoothly during the test programme; the Handley Page automatic slats on the outer wing panels were not necessary, and were wired shut (they can be seen to this day); there was vibration at high speed caused by disturbed airflow behind the short engine nacelles, but this was cured by fitting longer, more aerodynamic ones. W4050 showed blazing speed – 30 mph faster than the RAF Spitfire of the day – and was highly manoeuverable, too. When it was demonstrated in front of a mixed group of British and American military personnel, it screamed across the airfield at 400 mph, then performed a series of upward rolls – with one engine feathered! General H. H. Arnold was there, and tried very hard to have the Mosquito built in the United States (it was rejected by all the U.S. companies which were approached as being ‘made from an out-dated material’) Later the USAAF would operate both British and Canadian-built Mosquito aircraft.

By December 1940, the aircraft’s upper surfaces had been painted in the standard RAF Dark Earth/Dark Green camouflage pattern, and it was readied for its official trials, which would take place at the Aeroplane and Armament Experimental Establishment, RAF Boscombe Down. Then came a most unfortunate mishap; on 24th February, 1941, following a routine landing, the tailwheel caught in a patch of rough ground, and the rear fuselage was severely fractured near the rear fuselage hatch. The machine was rebuilt using the fuselage from the next machine on the line (the photo-reconnaissance prototype), and a strengthening ‘strake’ fitted externally (visible on every Mosquito); a special, low-drag Dunlop-Marstrand tailwheel was also fitted. A heavy landing happened in May, 1941, further damaging the fuselage, which was repaired with a large plywood patch (still visible). Engine developments meant that W4050 was used to trial various R/R Merlins; in July, 1942, a pair of 2-speed, 2-stage supercharged Merlin 61s were flown, and on the 8th of August, 1943, when fitted with two Merlin 77 engines, the prototype became the fastest Mosquito in level flight, ever – 439 mph! By December, 1943, W4050’s usefulness had come to an end, and she was retired.

She stayed at Hatfield for a while, fitted with Merlin 25 engines like the standard fighter-bomber version, the FB.VI, and was used to teach apprentices. Post-war a long period of storage at Hatfield, Chester and other company sites ensued. W4050 was publicly exhibited at the Society of British Aircraft Constructors annual shows in 1946 and 1947, after the company bought it back from the Air Ministry. Unfortunately, plans to publicly exhibit it at Hatfield fell through, and orders went out for it to be burnt! By great good fortune, the new owners of Salisbury Hall, Walter and Audrey Goldsmith, were looking for some Mosquito parts to exhibit at their new home, and the company allowed them to acquire W4050, provided money could be raised for a small hangar. The £1,800 needed was quickly raised from friends and ex-aircrew, and W4050 came home. She formed the core of what has now become a major aviation museum, focusing on de Havilland aircraft, and machines from successor companies – the de Havilland Aircraft Heritage Centre.

Here she is, dismantled, and ready for a full restoration, the gap where the wing fits into her fuselage bridged by a special support rig, to prevent damage. When she emerges from her ‘cocoon’ she will be resplendent once again, all traces of the yellow marine-quality paint which was initially used to preserve her, gone. Despite the fact that there is more than a little of ‘George Washington’s axe’ about her, she IS the very first of a long, distinguished line – the de Havilland Mosquito.

If you would like to see a Mosquito in British skies, please consider supporting The People’s Mosquito Ltd, an Incorporated Charity in the United Kingdom. You can find out more, here:-



Thank you!

3 comments on “The start of it all – W4050, the Mosquito prototype”

  1. Nice, very nice, to see the Mossie which started it all is on display (even though only the fuselage). It would only be right for a flying Mosquito to be in the UK’s public trust to ensure the heritage of this greatly historic aircraft is properly seen to.


    • The rest of the components are stored, and the whole aircraft will be put back together soon! It is a most beautiful machine!


  2. W.J.S. (Bill) Baird, the Assistant Public Relations Manager at Hatfield, had become aware of the historical significance of the prototype Mosquito as early as 1945. When the aircraft was ordered destroyed he saved it from being burned, having it dismantled and then moving it first to Panshanger, then Hatfield for a short time, to the factory at Chester and finally back to off airfield storage at Hatfield.


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