Pay very close attention to what you watch on the History Channel and you will find that, often, their accuracy is.........suspect. 
Quick example...show on the AVG...said their P40b's were armed with 20mm.
However, they weren't flying P-40Bs..... Tomahawks, unique to the AVG... They got their own model, literally.
These fighters were not delivered with "government supplied equipment". IE: Guns, gun sights and radios. They were mostly equipped with commercial radios. Guns varied. All had two .50 cal Brownings, but there was a shortage of common caliber wing guns. So, some flew with US .30 cal (M1906 ammo) Brownings, some were fitted with British .303 Brownings and about 50% were armed with 7.92mm Brownings (standard Chinese caliber as adopted from Germany in 1899).
Curtiss built several variations of the P-40/Tomahawk.
H81: P-40/P-40A
H81B: P-40B and P-40C
H81A-1: Tomahawk I, Tomahawk IA, Tomahawk IB
H81A-2: Tomahawk IIA and Tomahawk IIB
H81A-3: AVG Tomahawks
Many historians have assumed that since the AVG planes came from a British order, they were Tomahawk IIB types as the serial numbers indicate. Wrong assumption. Serial numbers were assigned upon acceptance of the British contract, well before any procurement or manufacturing occurred. Since the Chinese didn't specify some of the items called for in the Brit contract, Curtiss didn't build them to the British specification. They had on hand, a large stockpile of externally seal fuel tanks remaining. These were written off when the USAAF contract specification was amended to require internal sealing of fuel tanks and the addition of plumbing and mounting for an external drop tank.
Curtiss nearly scrapped these, but the Chinese specification provided a use. In addition, engines were not available as Allison's entire production was already allocated. At considerable expense to the Chinese, Allison agreed to set up a special assembly line for manufacture of 170 engines (100 to be fitted and 70 spares). Additional engines would be backlogged into the regular production, but would not be available prior to 1942. This production line would build engines without much of the special tooling found on the main line. To facilitate faster delivery, Allison used parts rejected for the main line for tolerance discrepancies. To use these parts, the engines would have to carefully hand built, matching parts.
When the first engines were ready for run-in testing on the dynometer, Allison was stunned to discover that every engine produced between 1,225 and 1,270 hp. In some cases, more than 200 hp greater than the standard V1710-33 coming off of the main production line. A good thing, right? Well, yes and no. Yes, because the extra power enabled AVG Tomahawks to reach almost 370 mph as opposed to the 350 mph of the P-40B, or 340 mph for the heavier, higher drag P-40C/Tomahawk IIB. A bit better climb and acceleration were also added benefits. There was a downside. Allison knew that the spur geared reduction gear assembly of the V1710-33 was not designed for more than 1,100 hp (which is why the P-40D/E employed the V1710-39 with much stronger helical cut reduction gearing). They never said anything to the Chinese about this potential problem.
In service with the AVG, as hours piled up on engines, reduction gears began failing; shearing teeth. At least 17 AVG engines suffered these failures and 5 Tomahawks were written off or damaged in crash landings as a result. That was more than 20 times the frequency of failure seen for American and Brit models, where engines were worn out before the reduction gears required repair.
Trust me, you'll never get that type of history on any television show....
My regards,
Widewing
