Cloth covered biplanes are still in front line service at the start of WWII, and unlike most people I count the winter war as the starting of it, but here or there biplanes served pretty deep as front line combat aircraft. If in may of '41 you send biplanes off to put a world of hurt on "the most advanced battleship in the world" that is a front line unit. Before that they put a world of hurt at taranto, this was the world third largest and a very modern navy at the time IIRC.
The american planes did well in the USSR, and they (the commies) went to great pains to down play the aid. There the air war did not reach as high as it did in the west. For the most part it was all ground support on the east.
