The first VVS combat regiment to operate the Airacobra was the 153rd IAP that had been in action at Leningrad and was reformed by the 22nd ZAP, beginning on 25Mar42. The regiment completed type training by 10Jun42 and departed for the Voronezh front. Contrary to popular belief, the Airacobra was not used solely for ground attack, either then or later, by its new Soviet operators.
Nobody doubts that the P-39 was used as a fighter or ground attack escort, but there seems to be plenty of literature around corroborating a ground attack role though it seems strange to me that such a role was ever doubted in the first place.