I found this page while researching this post:
http://airspacemag.com/issues/1990/d...h_1.php?page=9
From the page:
"Other U.S. and British pilots have claimed to have done it as well, recalling flights in Spitfires, P-38s, P-47s, and P-51s. But there is one basic, irrefutable reason why their claims are, as Fisher might have put it, malarkey. A propeller—even one designed to current state-of-the-art standard for maximum efficiency—continues to create thrust up to a point somewhere short of supersonic. At that instant, it suddenly loses efficiency and begins to create not thrust but enormous drag. “It becomes a flat plant,” Fisher said; “a big brake.” One Spitfire pilot, who attained the highest verified speed, Mach .9, achieved by a World War II propeller-driven aircraft, discovered this in a big way when the sudden braking forces became so powerful during a dive that the entire propeller and most of the engine cowling broke off."
The fact that the WWII planes had to DIVE to reach very high speeds may explain the claim of supersonic speeds:
"So were the P-47 pilots fibbing? Not at all, Fisher (and Johnson) explained. They were tricked by a simple phenomenon: airspeed indicators don’t function reliably in high-speed dives. The airplanes are falling so fast they can’t measure static air pressure quickly enough: while the instruments were down here, they were still measuring air from up there. Had neophyte Hurtienne’s indicator been accurate at an indicated 675 mph at 20,000 feet, for example, his true airspeed would indeed have been at least Mach 1.05 at typical temperatures. But it wasn’t. Because the airspeed calculation would have been based on an artificially high altitude reading, the airspeed indicator would show the airplane to be traveling faster than it really was."
So, while the Jug is my favorite WWII aircraft, it probably is not feasible for it to reach or exceed the sound barrier, no matter what the circumstance.
tbm