The Q series became the most numerous and advanced of all the Airacobra family. It was a direct successor of the N series. The whole propeller-engine group remained unchanged: the Allison V-1710-85 engine, the reduction gear, the elongated shaft and the Aeroprop type propeller. Because of this, the flight characteristics remained virtually unchanged. However, a more efficient four-bladed propeller was fitted to the series from Q-21 to Q-25. As for the alterations, they mainly concerned the armament. The inefficient wing machine guns of rifle caliber were removed and usually replaced by two 12.7 mm Brownings in pods under the wings. But these were not always fitted. Most of the aircraft sent for export to the USSR had no wing machine guns. The suspension tank of 87 gallons was replaced by the standard 120 gallon tank. A tank of 110 gallons (416 l) capacity was used in the Q-5 series.
The differences between the various Q series consisted mainly of the search for the optimum combination of armor protection and internal fuel tank capacity. Takeoff weight, range and load varied from version to version. Altogether, beginning with Q-1 and ending with Q-30, eight series of the fighter were built, to a total number of 4699 aircraft. Of these, 3291 were exported to the USSR. Furthermore, a few reconnaissance versions of this aircraft, fitted with photo-cameras, were built on the basis of the Q series.
This aircraft was not used at all in Great Britain, because the high-altitude speed characteristics of the Cobra were considered unsatisfactory. The US Army Air Corps used the aircraft mainly in the Pacific, in places in which it was impossible to use any aircraft other than the Cobra because of the condition of the airstrips, where the P-39, because of its tricycle landing gear, had no difficulties. Nevertheless, the American pilots feared and disliked the aircraft, calling it “Dogchain” because of its rear-mounted engine and rear centering. Cases were known of the aircraft being deliberately crashed to speed up re-equipment with the more popular P-38.