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.