Just as a thought experiment, I was wondering what the requirements for supplying the Allied Expeditionary Force in NW Europe during WWII entirely by air would look like, in terms of number of transports per division and overall.
A WWII division might require 600 tons of supply per day, just as a ballpark figure. A C-47 could carry about 3 tons per sortie. That's 200 sorties per day, or one every 7 minutes per division. The distance between London and Paris is about 214 miles, and a C-47 cruises at 160 MPH. I wouldn't think making that distance would take more than 2 hours per sortie, but definitely open to correction there. It would reach 10,000 feet in about 10 minutes.
With all this in mind, would assuming 4 sorties per day per aircraft be realistic? I don't know how long it would take to load the supplies onto the aircraft, get them off, and get it back in the air again for the return journey; those are obviously significant limitations. Assumption is that the divisions would have enough organic transport to get the supplies from the airfields to the regimental depots etc.
If 4 sorties/aircraft/day is realistic, you'd be looking at 50 C-47s per division; with ~65 divisions on the Western Front, that's 3,250 aircraft. How much supply would forces outside the divisions require relative to the divisions?