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General characteristics
Crew: One
Length: 30 ft 2 in (9.2 m)
Wingspan: 34 ft 0 in (10.4 m)
Height: 12 ft 5 in (3.8 m)
Wing area: 213 sq ft (19.8 m²)
Empty weight: 6,516 lb (2,955 kg)
Loaded weight: 7,570 lb (3,433 kg)
Max. takeoff weight: 8,400 lb (3,800 kg)
Powerplant: 1 × Allison V-1710-85 liquid-cooled V-12, 1,200 hp (894 kW) at 9,000 ft (using emergency power)

Performance
Never exceed speed: 525 mph (845 km/h)
Maximum speed: 389 mph (626 km/h) at 10,000 ft (using emergency power)
Stall speed: 95 mph (152 km/h) Power off Flaps & undercarriage down
Range: 525 miles on internal fuel (840 km)
Service ceiling: 35,000 ft (10,700 m)
Rate of climb: 3805 ft/min (19,3 m/s) at 7,400 ft (using emergency power)
Wing loading: 34.6 lb/sq ft (169 kg/m²)
Power/mass: 0.16 hp/lb (0.27 kW/kg)
Time to climb: 15,000 in 4.5 min at 160 mph (260 km/h).

Armament
Guns:
1 × 37 mm M4 cannon in nose (firing through the propeller hub) with 30 rounds of HE-T ammunition.
2 × .50 cal (12.7 mm) synchronized Browning M2 machine guns, nose-mounted; 200 rounds per gun
2 × .50 cal (12.7 mm) Browning M2 machine guns (one each wing), 300 rounds per gun
Bombs: Up to 500 lb (230 kg) of bombs under wings and belly

Fortunately for Bell, the US Army was still interested in the aircraft. The Army ordered the P-39C as the first operational variant of the Airacobra, with the first aircraft entering service in January of 1941. Despite the troubled development, the P-39 still had a number of things going for it. The aircraft was still very maneuverable and had simply unrivaled firepower. The P-39C, and the YP-39 before it, were both built to carry the monstrous 37mm Automatic Cannon, M4. The M4 was the largest cannon ever fitted to a fighter by the US Army Air Forces in WW2. The 37mm was also complimented by a pair of synchronized .50 caliber and .30 caliber machine guns in the nose. The P-39 had a series of unique controls for the aircraft weapons. There were weapon selection switching allowing the pilot to select either the cannon, synchronized guns, wing mounted guns, or any combination thereof.

There is a legend that persists that the 37mm armed P-39s excelled as tank busters, particularly in Soviet Service, and this seems rather unlikely. Despite sharing a similar caliber to the gun found on the Stuart series of Light Tanks, the Oldsmobile M4 had noticeably inferior performance to the 37mm M3 mounted on tanks. There was a muzzle velocity difference of about 200 meters per second. The higher velocity M3 was already hard pressed to penetrate the armor on later models of German tanks. It doesn’t seem likely that the lower velocity gun on the P-39 would be particularly effective against tanks unless a hit was scored against the top of the engine deck or perhaps through the top of the turret.

Flying the P-39 for the first time had to be an interesting experience for most of its pilots. Unique for any fighter of WW2, the pilot entered the aircraft through either one of two doors located on either side of the cockpit. At first glance, this would appear to make bailing out of the aircraft difficult since the unfortunate pilot would be forced to open the door into a 300 mph headwind. Bell was quite aware of this, and there was a lever next to each door that would release the pins holding either door in place. They would either fall away themselves or with some assistance from the pilot. The pilot could then roll out of the cockpit and away from the aircraft.

The cockpit its self was well laid out. Despite its unconventional entry procedure, the aircraft did essentially have a bubble canopy. Compared to almost every other US Army fighter in service by 1940 (and indeed that of most other nations), the P-39 had simply unrivaled rearward visibility. The pilot’s view rearward was only partially obscured by radio equipment and the air intake for the engine, otherwise the pilot could almost see directly behind themselves. Only the P-38, and bubble canopied P-51s and P-47s would have the same level of rearward visibility in USAAF service. Also, on a very unique note, the pilot of the P-39 also had access to a funnel shaped relief tube if he felt the need to empty his bladder while flying.

In terms of flight characteristics, the P-39 was by most accounts actually a very pleasant aircraft to fly. P-39 variants were used extensively as trainers in the USAAF. However, it was certainly hampered by a relatively low airspeed. Most variants of P-39 could only achieve a maximum of 368 miles per hour in level flight. Despite its weight, the P-39 was also considered to be reasonably maneuverable and light on the controls. The aircraft also had decent stall characteristics. Stall speed was around 109 miles per hour and the aircraft could be quickly recovered at 145 miles per hour. Ground handling, particularly taxiing was superb. The pilots of nearly every other fighter (save for the P-38) were forced to zig-zag their aircraft left and right down the taxiway in order to see over the nose. With a tricycle landing gear, the pilot in a P-39 could clearly see over the nose.

The P-39 did have a bad reputation for having some nasty spin characteristics. There was a persistent rumor that, when entering a stall or a spin, the aircraft would enter an uncontrollable tumble from which the pilot could not recover. This reputation still exists in some capacity today. At the time, word of it was widespread enough in the USAAF that it warranted some testing. From August 1-3, 1943 a P-39 was put through an extensive series of tests attempting to recreate this legendary tumble. After about a thousand spins, USAAF test pilots were unable to recreate this mythical tumble. The Army concluded that the P-39 had normal spin characteristics for a pursuit aircraft and recovery from a spin could be achieved in two and a half rotations provided the proper recovery characteristics. Additionally, the ‘tumble’ likely a misinterpretation of the inverted spinning and snap rolls of an improper spin recovery.

The first P-39 Airacobras to actually enter the war saw action with the Royal Air Force as the Airacobra I. These aircraft, designed specifically for export featured an underpowered Allison V-1710-35 churning out a 1,150 horsepower. Also the aircraft used a Hispano Suiza 20mm instead of the 37mm M4. Armament was upped from the P-39C. The nose .30 calibers were exchanged for a quartet of .303 machine guns in the wings. The .50 caliber machine guns in the nose still remained. Airacobra Is entered service with No. 601 Squadron in August of 1941 and were almost immediately withdrawn from service. 601 Squadron’s Airacobra saw action in all of four sorties over France. The RAF derided the aircraft’s anemic performance over 12,000 feet, low airspeed of 355 miles per hour and short range. The Airacobra I was withdrawn in March of 1942. The remaining airframes were either given to the Soviet Union or back to the USAAF where they were designated as the P-400. The secondary armament was switched out once again for the .30 calibers that were standard in USAAF service.