Some interesting points:
- I just don't see the RAF ordering bombers from the US in time for France 1940. Earlier they were impressed by the B-10 and used it's capabilities to get the British Aircraft industry to modernise. Yet, there was (AFAIK) no interest in the A-17 or A-18 i.e. 'attack' aircraft with forward firing weapons. When the BPC went to the US they were impressed with the speed efficiency of Lockheed and ordered what became - the Hudson, though when it was announced there was a lot of opposition.
- You might think there was more benefit in co-operation with production with France, but we are looking with 'modern eyes' to with the view of the time - how can you sell Blenheims to Finland and Yugoslavia when you're buying it's competitor the Potez 630 series.
The French bombers of the period tend to be much maligned, but that was the IMO the older ones i.e. Farman, Bloch 210, whereas the Bloch 174, Amiot 350 series, Leo 451, and stubby Bregeot 690 series - in numbers, in the right (trained) hands, and fully sortied could have done well.
As mention RAF attitude and tactics didn't help! But then, they didn't want to send an Air Component to France if they could help it. Perhaps too a side effect of the dividing the air force into Bomber Fighter Commands etc., meant that Bomber Command had no Fighters, and Fighter Command had no Bombers!
It has been suggested about the 'Stuka' - the nearest the RAF came to having one was the Henley (surprised no one's mentioned it) - yes granted it would have needed a different attitude to DB, but it could have been there in stead of some of the Battles. A mixed formation of Henleys Hurricanes would be confusing to the Germans!!
Also, re: flak - to me it seems physically easier to track a low-flying or shallow diving aircraft i.e. from right-to-left, than it would be to track from up - to - down a diving aircraft!
It's pushing plausibility to get the Mosquito or Beaufighter early enough - but maybe the Supermarine 313 - able to carry bombs internally, or the Gloster twin to the earlier Turret spec - "could it carry bombs".
And, maybe Blenheim with better engines, or (as said earlier) Bristol P.13/36 - Bicester or Buckfast ?
Any other 'projects that could help!