USA combat aircraft

Dave, can track it further back than that. Shark mouths on aircraft date at least as early as World War I, which is the first occurrence mentioned in my sources. While I think it is safe to say that the American Flying Tigers during World War II brought the style to the peak of prominence, the first recorded use was in fact German around 1916, found on a Roland C.II, flown by Ritter von Schliech, although it is a pretty lame rendering, compared to later versions, as it is really just a black line roughly comparable to a mouth. It seems to have been popular with the Roland C.II, and a number of the aircraft carried it, as well as a more robust, 'teethed' version on some as well.

At roughly the same time, at least one British aircraft used the Sharkmouth design, one of the butt-ugly Maurice Farmans, serving with the Royal Naval Air Service in the Med. This is the 'teethed' style. It doesn't seem clear who the pilot was, but apparently he was the only one who did it to his aircraft, and it wasn't found on other machines from the Wing. A few examples can also be found here and there of French and American uses, but again, it wasn't that widespread.

Sharkmouths from WWI were an individual application, it wasn't a group scheme until JGr126 (ZG26) applied them as a unit.

The sharkmouth did pop up on a few Roland C.II (Wahlfisch) types, but again, it wasn't a standard unit scheme.

That strangest P-40 I ever did see.
That undercarriage just far too narrow. Why would they change from the P-36? Shows that Americans made a mistake. And why are the techs in German uniforms? Fancy dress? And when did the P40 have 2 bladed prop?
The exhaust stubs are far too low. When did the Allison go inverted?