The USSR got 212 of the ex-RAF order of Aircobras, and the USAAC got 179 of that order. 100 of the USAAC P-400s were shipped to the Pacific.
So it was a major sub-varient. Used in the SW Pacific and Eastern Front.
...small compared to the 4000 P-39Qs made.
You could go with a P-39D as well, but you could also go with the P-400. I just think the P-400 is the more interesting.
There is also the P-39D-1 (20mm armed) that went to the USAAC and the VVS. Several hundred built, there are photos of them in the SW Pacific. Boyd Wagner flew a P-39D-1 from New Guinea.
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"Why should it be able to reach 392mph?
The more common figure seems to be 376 mph (TAS) at 15000 ft and 325 (IAS) at deck?"
...you are quoting the P-39D, not the P-39Q.