As I read it they did trial it and did form a squadron of them with the smaller 20mm canon, which was required to standardise the canon in use. The squadron never settled with it – there were serviceability problems and with new Spitfires becoming more available I presume the big disadvantage of its high altitude performance was not matched by its ground attack potential.

Didn’t the later model P40s serve in the role you suggested for the P39 in the desert?