After being brought up by Shay on the WIX forum, some very interesting details spotted by the expertise and eye of several posters. It may be a cliche, but it's also true that different people see - and pull out - different things from the same image. (The full size photograph, part of the Life archive on Google, and useful for the points made, is to be found here.)
"I like the Cletrac M2 High Speed Tractor too! We are slowly restoring one here. In fact the engine just came back from the overhaul shop today.Meanwhile, Ryan Harris said; "Notice the over sized stars and bars under BOTH wings." and Brandon Kunicki responded to a question on the gun barrel alignment (a unique configuration on the P-47 anyway); "Looks like they are servicing the guns so they may have the barrels out or are in the process of removing/reinstalling the entire gun."
The Cletrac has a high pressure (adjustable up to 2000 psi) engine driven air compressor on the back for tires, air tools and servicing the struts, which looks exactly like what he is doing. The line he is holding leads to the receiver cylinder and controls that are mounted on the left front fender.
The large bottle on the right front fender is a modification. I have seen other Cletracs with oxygen bottles mounted on the right side for servicing the O2 systems so I would wager that's probably an oxygen cylinder.
The Cletrac also had an engine driven generator on the right front fender which put out 115 volts DC for running lights and certain power tools. This tractor was quite the service vehicle for the AAF and went on into Korea.
Sorry if I hijacked a thread about the P-47. I think the Cletrac and the jug were probably designed by the same folks since they were both built like a tank!
I really like the nose art on the 500 pound GP's on the wing racks. I wonder if they did this for the Life photographer or was it just the normal routine?"