They depict aircraft of the 22nd Bombardment Squadron based at Hamilton Field, California, in early 1941; the 42nd Bombardment Squadron based at Hickham Field, Hawaii, in early 1941, the Air Corps Materiel Division at Wright Field in 1940 or 1941, and a B-17C dressed up (not very authentically) as an RAF Fortress Mk. I for a publicity tour of the US to drum up public support for American aid to the British.
Skins by Mick, who just added some markings to Shessi's textures.