Warbird Information Exchange

The designation P-40G was given to 44 existing Army P-40s that were fitted with H81-A2 Tomahawk IIA wings that carried four 0.30-inch machine guns. The first such conversion was P-49 39-221, which was assigned the unofficial designation XP-40G. The remaining 43 retrofits took place between August and September 1941. Company records refer to these conversions under the designation Model 81-AG. Serials of P-40s retrofitted were as follows:

39-162,176,181,187,190,191,196,197,204,206,209,217,220,221,226,235,238,
248,257,263,267,275,276,279,288 and
40-292,297,299/301,303,309,315,318,320,323,331/333,335/338.

Some sources have at least some of these P-40Gs being assigned new Army serial numbers after these modifications were completed. These new serial numbers included:

42-14261/14274 Curtiss P-40G Warhawk
42-14277/14278 Curtiss P-40G Warhawk
42-14281 Curtiss P-40G Warhawk

However, these numbers conflict with those assigned to an order for P-40L-30-CUs which was cancelled.

Sixteen of these P-40Gs were shipped to the USSR starting in October 1941. All those examples remaining in the USA were redesignated RP-40G in October 1942, where the R meant "restricted from combat use".

39-221 was shipped to the USSR in 1943.

For some reason, the designation P-40H was never assigned. The designation P-40I was never assigned in any case, lest the letter "I" be confused with the number one.
Source: http://www.p40warhawk.com/Variants/P-40G.htm


Curtiss P-40G 42-14264 remanuf. from P-40 wo 31 Mar 1943 at Luke AAF, AZ.


Also this nice photo of 9184, but I'm not sure what the 9184. it doesn't seem to be 39-184 according to Baugher that's a Curtiss P-36C.

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“PMURT KCUF”

39-184 wasn't a P-36C; its record card shows it with V-1710-29 engine and it should be a P-40A on Contract W-535 ac-12414 of 24Jun39.

Its record card is as follows:

Received at Contractor 26Jun40
Assigned to Langley AAF 01Jul40
Assigned to Mitchel Field 23Nov40 (35th PS)
Wrecked at Mitchel Field 11Apr41 – landing accident (1/Lt Lenord C Lydon)
To Fairfield Air Depot for repair
Assigned back to Mitchel Field 24Oct41
Assigned to Langley AAF 06Feb42
Assigned to Baton Rouge 06Feb42 (56th PS)
Republic (?) Feb42
Wrecked at Harding Field 21Mar42 – ground loop (2/Lt Ferdinand Beldon Paris)
Wrecked at Harding Field 24Apr42 – nosed-up on landing (2/Lt Don Buie Michael Wood)
Assigned to Charlotte AAF 30May42
Assigned to Luke Field 23Jun42 (544th Advance Flying Training Sqn (SE))
Wrecked at Luke Field 25Aug42 – ground loop (Russell B Kraus)
Redesignated RP-40 (date not known)
Wrecked at Luke Field 22May43 – a/c forced landing-ship caught fire in air-major damage (Dominick J Lieto)
To Class 26 at Luke 21Jun43 with 501 hrs
Luke to survey 30Jun43; assumed scrapped

Incidentally, those "42-142**" aircraft are recorded as P-40Gs "picked up per Budget Report 12/26/41" so it seems that the AAF just re-used vacant serial numbers for them.