This is a historical question rather than an Aces High discussion. It seems that the American aircraft industry during the Aces High period was very much in favour of combat flaps, manoeuvring flaps, what-have-you. All of the American planes have extremely useful flaps that can be deployed at high speed. It bolsters my psychological impression that the American planes are more solidly-built than the others.
In contrast, the other nations did not seem too hot on the idea of high-speed combat flaps. The British aircraft seem to have flaps that were designed purely for landing and take-off. (I have just been reading "First Light", a book by WW2 Spitfire pilot Geoffrey Wellum. He describes his part in Operation Pedestal, in which a flight of standard land-based Spitfire Vs were flown from HMS Furious in order to reinforce the defence of Malta. In order to take off from the carrier, the flaps were held in an intermediate position with wooden chocks; once airborne, the pilots opened the flaps fully so that the chocks could fall out. (Just as Wellum takes off, one of the other carriers, HMS Eagle, is hit and sunk by a U-Boat.))
The Messerschmitt and Lavochkin designs have leading-edge slats but again the flaps seem to have been designed more for landing or very slow-speed manoeuvres under adverse flying conditions. I haven't read very many historical accounts by109 pilots but I get the general impression that they did not expect to use the flaps whilst fighting. This is particularly galling in the case of the late-model 109s, which would benefit from high-speed flaps. And the same is true of the 190s, especially given their poor turn radius.
I suppose the Japanese designers felt that their aircraft turned well enough without having to use flaps. Perhaps the people at Hawker and Supermarine felt the same way. But it seems odd that the trend of useful high-speed flaps is so dominant amongst American planes; what was the general philosophy amongst American aircraft designers in the run-up to WW2?
