Warbird Information Exchange

So kind of an odd question, the P-47D-23-RA sitting in our hanger is a war veteran that crashed in Papua New Guinea during the war. It's been sitting in front of a guy's house in PNG since then and hasn't flown since. We're finally cracking it open and we just found an extra fuel or chemical tank in the dorsal area right behind the cockpit. There is an opening for the tank fill on the center-line behind the cockpit canopy. The canopy would need to be closed to fill whatever was in the tank. I'd estimate that it holds 40 or 50 gallons, it's not huge.

Normally the P-47 only has two fuel tanks and they are both below the cockpit. We can't find a reference to an extra tank of any sort behind the cockpit. As far as we know the airframe is bone stock and hasn't been modified.

Opening:
http://i.imgur.com/k2ecaFh.jpg

Filler cap:
http://i.imgur.com/nHApKze.jpg

Here you can see the outside of the tank under the skin:
http://i.imgur.com/7z3J8U8.jpg

Water-alcohol tank??

The main water injection tank is on the firewall, and we have confirmed our airframe had that.

Field installed Beer Keg? (sorry, had to)

For C and D, is this not the compartment for the oxygen cylinders?.(EMM 43)
At the top, this is not a filler cap but access door to connect or disconnect the tubes to the cylinders.

Oxygen tanks are just behind this tank.

Well after see the spits with beer kegs on the wings that would have been my first comment. But I'm wondering if it might be some kind of high pressure dry air emery bottle but that would have listed in the maint books I'msure .

I was able to get some info from someone at hyperscale. Gen George Kenney of the 5th Air Force didn't like how short the combat radius of the P-47 so he had his engineering staff devise a couple different method's to extend the range. One was a 200 gallon drop tank designed and built by Ford of Australia. Another was this tank which was test fitted to several P-47's. It ended up giving the plane balance problems because it was too high up in the fuselage and it wasn't self sealing so it became a fire hazard. It was quickly dismissed and never used on a large scale. Turns out ours was one of the test models.