In any early war British aircraft production changes ideas an over riding consideration is to have the production line working at the latest in May 1940, otherwise it runs into the Battle of Britain freeze orders in a big way, something that did delay the Mosquito.
De Havilland pitched the idea for a military version of the Albatross airliner in mid 1938, wooden construction, twin Merlin but for bomb loads of 4,000 pounds or twin torpedoes, there were variations on this, size and armament, the October 1938 version with twin Merlin X, 3 crew and defensive guns was calculated to reach 300 mph. Also proposed was a twin Merlin version of the all metal Flamingo, smaller and faster. The pitch for an even smaller twin Merlin version was made in September. A year later the unarmed wooden design with 1,000 pounds of bombs was being quoted as reaching over 400 mph on a pair of 1,145 BHP engines.
The first production Mosquito PR.I were accepted in July 1941. That means starting the design process at least 14 months earlier than September 1939, that is mid 1938, to have first production by May 1940.
Next obstacle is the ramp up to mass production. To end June 1942 there were a total of 139 Mosquito built, including prototypes, 10 PR, 91 fighters, 29 bombers, 9 trainers, counting W4050 as a bomber. Production to end 1941 was 23 including 3 prototypes and a trainer. If you want the Mosquito around in numbers in mid 1940 start development in mid 1937 at the latest. Given the situation do not expect many bombers in 1940.
Rolls Royce Derby started Merlin X production in 1938, with 27 built by the end of the year, another 283 by end 1939 when production ended there, Crewe starting production in October 1939, with 108 by end of year, production ended in December 1942. The first Merlin XX were built at Crewe in July 1940, with 332 made by end of year, Glasgow 6 more November and December, Derby 1 in December.
Using Rolls Royce figures, 2,572 Merlin built in 1939, 2,196 being Merlin III, and as expected it was end loaded, 1,141 Merlin built in the final 4 months of 1939.
There were 33 Whitley IV (Merlin IV) built May to August 1939 then 7 IVA (Merlin X) and the first 8 Whitley V in August 1939. The report is only 73 Merlin IV built, all by Derby in 1938.
The RAF in France lost 34 Battle to all causes up to 9 May 1940, of these 8 were day reconnaissance sorties 20 to 30 September 1939, all shot down by fighters (including 1 joint French/German effort). After that it was all non combat and from 1 March 1940 all at night. Looks like reconnaissance was handed over to the Blenheim units, which lost 8 aircraft on the duty October 1939 to January 1940. Then come the losses from units based in Britain.
The RAF began the migration to 2 pitch then constant speed propellers pre war with its heavier aircraft first, the Hurricane changed over to constant speed end February 1940, it looks like the idea was the Spitfire I would stay 2 pitch, the mark II introduce the constant speed propeller.
Australia did not build any DH.94 Moth Minor as such, several had been ordered pre war by civil users, an initial production run was put in place to blend local wooden and imported metal parts to fill civil orders, with 4 being assembled when the war began. The cancellation of Moth Minor production in Britain offered the chance to acquire lots of now surplus parts and an order was placed in October 1939 via DH Australia for 50 under Overseas Indent 757, it was soon curtailed as it became clear the Tiger Moth was better. DH in Britain cabled in October 1939 that 22 finished machines and 20 incomplete sets were being shipped, in November 20 complete aircraft ready to sail, 3 more due to sail and 3 packed ready for shipment, there were 22 with dual control and "a few" with rudimentary blind flying instruments. The incomplete September 1939 to March 1940 British export reports have 30 Moth Minor sent to Australia. In the end 46 were around with 42 serials issued, including for impressed civil aircraft.
The RAAF ordered a total of 66 Avro Cadet as its trainer between 1935 to 1938 of which 32 were cancelled, then in 1939 it ordered 20 Tiger Moth fuselages and engines from Britain to be fitted with locally made wings, when war was declared more Tiger Moths were ordered from Britain and also DH Australia.
DH were building Tiger Moths for the RAF, 88 in 1938, 674 in 1939 and 663 in 1940 (production ending in August except 1 in December), plus overseas and civil orders. Add 59 Queen Bee in 1938 and 139 in 1939, 50 Don in 1938/39, 178 Oxford in 1939, all for the RAF.
