Please, do some research before making these claims. The P-39 was most certainly not designed as a ground attack aircraft.
I appreciate your comment but:
Bell P-39Q Operational history
The Airacobra saw combat throughout the world, particularly in the Southwest Pacific, Mediterranean and Russian theaters. Because its engine was only equipped with a single-stage, single-speed supercharger, the P-39 performed best below 17,000 feet (5,200 m) altitude. In both western Europe and the Pacific, the Airacobra found itself outclassed as an interceptor, its earliest proposed role, and the type was gradually relegated to other duties. It often was used at lower altitudes for such missions as ground strafing.
Larry Bell did intend for the 39 to be an intercepter, but having insisted on a single stage blower, instead of the two stage, to save weight, the 39 was more or less restricted to altitudes of less than 10,000 feet.
It was used almost entirely thoughout the war as a ground attack aircraft,(check the Russian stats on the 39), and proved to be a very effective ground attack aircraft!
In 1940, the British Direct Purchase Commission in the U.S. was looking for combat aircraft; they ordered 675 of the export version Bell Model 14 as the "Caribou" on the strength of the company's representations on 13 April 1940. The British armament was two nose mounted 0.50 in (12.7 mm) machine guns, and four 0.303 in (7.7 mm) Browning machine guns in the wings; the 37 mm gun was replaced by a 20 mm (.79 in) Hispano-Suiza.
British expectations had been set by performance figures established by the unarmed and unarmored XP-39 prototype. The British production contract stated that a maximum speed of 394 mph (+/- 4%) was required at rated altitude. In acceptance testing, actual production aircraft were found to be capable of only 371 mph at 14,090 ft. To enable the aircraft to make the guarantee speed, a variety of drag reduction modifications were developed by Bell. The areas of the elevator and rudder were reduced by 14.2% and 25.2%, respectively. Modified fillets were installed in the tail area. The canopy glass was faired to its frame with putty. The gun access doors on the wing had been seen to bulge in flight, so they were replaced with thicker aluminum sheet. Similarly, the landing gear doors deflected open by as much as two inches at maximum speed, so a stronger linkage was installed to hold them flush. The cooling air exit from the oil and coolant radiators was reduced in area to match the exit velocity to the local flow. New engine exhaust stacks, deflected to match the local flow and with nozzles to increase thrust augmentation, were installed. The machine gun ports were faired over, the antenna mast was removed, a single piece engine cowling was installed and an exhaust stack fairing was added.
ell-P-39 from the United States requisitioned 200 aircraft of the order destined for the UK, adopting them as P-400s (named for advertised top speed of 400 mph (644 km/h)). After Pearl Harbor, the P-400 was deployed to training units, but some saw combat in the Southwest Pacific including with the Cactus Air Force in the Battle of Guadalcanal. Though outclassed by Japanese fighter aircraft, it performed well in strafing and bombing runs, often proving deadly in ground attacks on Japanese forces trying to retake Henderson Field. Guns salvaged from P-39s were sometimes fitted to Navy PT boats to increase firepower. Pacific pilots often complained about problems of performance and unreliable armament, but by the end of 1942, the P-39 units of the Fifth Air Force had claimed about 80 Japanese aircraft, with a similar number of P-39s lost. By any standard the Airacobra and its pilots held their ground against the Japanese. Fifth and Thirteenth Air Force P-39s did not score more aerial victories in the Solomons due to the aircraft's limited range and poor high altitude performance.
While I may have mis-spoke about it being "designed" as a ground attack aircraft, that is what it wound up being and was very, very effective.
