Since we've done the RAF, LW and the Japanese to death, let's talk about 'Muricans.
Starting by the fall of France (armistice was signed on
22th May 1940*), as a newly appointed chief of the USAAC, you have the task of developing the best air force the world has seen. As with all the fiction vs. reality, it actually has to make a sense

The basic engines, produced or about to be produced are as given historically, feel free to mix and match engine numbers, layout and available supercharging of the era - non-historical engines are
not allowed. American-made guns & electronics of the era - no Chain guns or MK 108s etc. Cater for the need of bomber, fighter, attack and transport branches. Make the most from the designs already in pipeline, but new designs are also encouraged. The aircraft orders from other countries are respected. Try to channel the air war experiences from Spain, China, West Europe as much as possible towards training, strategy & equipment. You know that a global, war where USA is involved, is imminent.
* my mistake - armistice was signed on
22th June 1940