Was the RAAF the 4th largest air force in the world at the close of WW 2?

Actually, the RCAF was larger than the RAAF at that time. The rankings would be 1) USA, 2) RAF, 3) USSR, 4) RCAF, and, probably, 5) RAAF. Of course, that dismisses the air forces of the Axis powers, as both Germany and Japan had more aircraft than the RAAF. BTW, it is possible that the USSR was number 2, but that information is not readily available.