The Bell P-39 Airacobra was a World War II-era fighter aircraft developed by Bell Aircraft for the United States Army Air Forces.
It stood among the primary American fighters at the onset of U.S. involvement in the war.
Notably, the P-39 saw extensive service with the Soviet Air Force, which achieved the highest number of aerial victories attributed to any U.S.-built fighter in any conflict.
Other prominent operators included the Free French Forces, the Royal Air Force, and the Italian Co-Belligerent Air Force.
One of the P-39’s most distinctive features was its unconventional design: the engine was mounted mid-fuselage, behind the pilot, and connected via a drive-shaft to a nose-mounted propeller.
It was also the first fighter aircraft to be equipped with a tricycle landing gear configuration.
Despite the innovation, the design lacked a capable turbo-supercharger, restricting its performance at high altitudes.
Consequently, the Royal Air Force declined its use in Western Europe.
However, it proved well-suited to the Soviet Union’s air combat environment, which favoured engagements at medium and lower altitudes.
The P-39, along with its successor, the P-63 Kingcobra, remains among the most successful fixed-wing aircraft ever produced by Bell.
Operational History and Combat Performance
The Bell P-39 Airacobra saw widespread action across multiple theatres during World War II, including the South-west Pacific, Mediterranean, and Eastern Fronts.
However, its performance at high altitudes was compromised by the use of a single-stage, single-speed supercharger, limiting its effectiveness above 17,000 feet (5,200 meters).
In Western Europe and the Pacific, the aircraft was often outclassed by enemy interceptors and gradually transitioned away from air superiority roles.
Instead, the P-39 found its niche at lower altitudes, where it was frequently employed in ground-attack and strafing missions.
Variants
XP-39
Bell Model 11, one prototype 38–326 first flown 6 April 1938.
Powered by a 1,150 hp (860 kW) Allison V-1710-17 engine and was fitted with a General Electric B-5 turbo-supercharger, creating a two stage supercharging system similar to the P-38
(engine-mounted mechanical supercharger, remote exhaust-driven turbo-supercharger as a second stage for high-altitude)
Aircraft remained unarmed.
Later converted to XP-39B.
XP-39B
One conversion first flown 25 November 1939.
Streamlined XP-39 based on NACA wind tunnel testing resulting in revised canopy and wheel door shape, oil cooler/ engine coolant radiator intakes moved from right fuselage to wing roots, fuselage increased length by 13 in (330 mm) and decreased wingspan (by 22 in (560 mm).
The turbo-supercharger was removed, and the single-stage, single speed, supercharged 1,090 hp (810 kW) Allison V-1710-37 engine remained.
The carburettor air intake was moved behind the canopy.
YP-39
Bell Model 12, service test version, 1,090 hp (810 kW) V-1710-37 engine.
Armed with an M4 37 mm cannon with 15 rounds, 2 × .50 calibre machine guns with 200 rpg, and 2 × .30 calibre machine guns with 500 rpg in the nose.
Wider vertical tail than XP-39B.
13 completed with the first flying on 13 September 1940.
YP-39A
One intended to have a V-1710-31 engine, but was delivered as a regular YP-39.
P-39C
Bell Model 13, initial US Army designation P-45 Airacobra.
First flown in January 1941, it was the first production version, identical to YP-39 except for 1,150 hp (860 kW) V-1710-35 engine.
Armed with 1 × 37 mm cannon, 2 × .50 calibre and 2 × .30 calibre machine guns in the nose.
Aircraft lacked armour and self-sealing fuel tanks.
Twenty were produced out of an order of 80, with the remainder completed as P-39Ds.
P-39D
Bell Model 15, production variant based on the P-39C with additional armour and self-sealing fuel tanks.
Armament increased to 1 × 37 mm cannon with 30 rounds, 2 × .50 calibre and 4 × wing mounted .30 calibre machine guns; 429 produced.
P-39D-1
Bell Model 14A, production variant fitted with a 20 mm M1 cannon instead of 37 mm cannon.
Specifically ordered for delivery under Lend-Lease.
336 produced.
P-39D-2
Bell Model 14A-1, production variant again intended for lend lease and fitted with 20 mm cannon, but with 1,325 hp (988 kW) V-1710-63 engine.
158 produced.
P-39D-3
26 conversions from P-39D-1 to photo reconnaissance configuration; K-24 and K-25 camera in rear fuselage, extra armour for oil coolers.
P-39D-4
11 conversions from P-39D-2 to photo reconnaissance configuration.
Same modifications as D-3 aircraft.
XP-39E
Bell Model 23.
three P-39Ds modified for ground and flight testing first flown 21 February 1942.
Intended for 2,100 hp (1,600 kW) Continental I-1430-1 engine but only flown with 1325 hp Allison V-1710-47 engine.
Used to test various wing and vertical tails.
Fuselage lengthened by 21 in (530 mm) and used in the development of the P-63.
The production variant, with the Continental engines was to be designated P-76; there was no Bell XP-76 as such.
P-39F
Bell Model 15B, production variant with three-bladed Aeroproducts constant speed propeller.
229 built.
P-39F-2
27 conversions from P-39F for ground attack and tactical reconnaissance.
P-39G
Bell Model 26, 1800 ordered, intended to be a P-39D-2 with a different propeller.
Later cancelled, with aircraft delivered as P-39K, L, M and N.
P-39J
Bell Model 15B, P-39F with 1,100 hp (820 kW) V-1710-59 engine with automatic boost control; 25 built.
P-39K P-39K-1
Bell Model 26A.
Fitted with an Aeroproducts propeller and powered by a 1,325 hp (988 kW) V-1710-63 engine.
210 built.
P-39K-2
Six conversion from P-39K-1 for ground attack and reconnaissance.
P-39K-5
One conversion with a V-1710-85 engine to serve as a P-39N prototype.
P-39L
P-39L-1
Bell Model 26B, similar to P-39K with Curtiss Electric propeller and higher gross weight.
250 built.
P-39L-2
Eleven conversions from P-39L-1 for ground attack and reconnaissance.
P-39M
P-39M-1
Bell Model 26D, variant with an 11 ft 1 in (3.38 m) Aeroproducts propeller, 1,200 hp (890 kW) V-1710-83 engine with improved high-altitude performance, 10 mph (16 km/h) faster than P-39L at 15,000 ft (4,600 m).
240 built.
P-39M-2
Modification of P-39M-1 for ground attack
P-39N
Bell Model 26N, originally part of the P-39G order.
1325 hp V-1710-85 engine.
10 ft 4 in (3.15 m) Aeroproducts propeller and different reduction gear ratio.
Starting with the 167th aircraft, the propeller diameter was increased to 11 ft 7 in (3.53 m) and internal fuel reduced from 120 to 87 US gal (450 to 330 L; 100 to 72 imp gal); 500 built.
P-39N-1
Variant with internal changes to adjust centre of gravity when nose guns were fired; 900 built.
P-39N-2
128 P-39N-1 converted with additional belly armour and cameras in rear fuselage.
P-39N-3B
35 P-39N converted with additional belly armour and cameras in rear fuselage.
P-39N-5
Variant with armour reduced from 231 to 193 lb (105 to 88 kg)
Armour plate replaced the bullet-proof glass behind the pilot
SCR-695 radio was fitted, and a new oxygen system was installed; 695 built.
P-39N-6
84 P-39N-5 converted with additional belly armour and cameras in rear fuselage.
P-39Q
The final production variant last one built in August 1944.
P-39Q-1
Bell Model 26E, variant with wing-mounted .30 calibre machine guns replaced with a .50 calibre with 300 rounds of ammunition in a pod under each wing.
Armour was increased to 231 lb (105 kg); 150 built.
P-39Q-2
Five P-39Q-1s modified to carry cameras for photographic reconnaissance by adding K-24 and K-25 cameras in the aft fuselage.
P-39Q-5
Production variant with reduced armour (193 lb (88 kg)), fuel capacity increased (110 US gal (420 L; 92 imp gal)).
Type A-1 bomb-sight adapters added; 950 built.
TP-39Q-5
One conversion to a two-seat training variant with additional cockpit added in nose – no armament.
Enlarged tail fillet and a shallow ventral fin added.
P-39Q-6
148 P-39Q-5s modified to carry cameras for photographic reconnaissance by adding K-24 and K-25 cameras in the aft fuselage.
P-39Q-10
Variant with increased armour (228 lb (103 kg)), fuel capacity increased (120 US gal (450 L; 100 imp gal)).
Automatic Boost controls added and throttle and RPM controls coordinated.
Winterisation of oil systems and rubber mounts added to the engines; 705 built.
P-39Q-11
Eight P-39Q-10s modified to carry cameras for photographic reconnaissance by adding K-24 and K-25 cameras in the aft fuselage.
P-39Q-15
Production variant with reinforced inclined deck to prevent .50 calibre machine gun mounting cracking, bulkhead reinforcements to prevent rudder pedal wall cracking, a reinforced reduction gearbox bulkhead to prevent cowling former cracking, and repositioning of the battery solenoid.
Oxygen system reduced from four bottle to two; 1,000 built.
P-39Q-20
Production variant with minor equipment changes.
The under-wing .50 calibre machine gun pods sometimes omitted; 1,000 built.
P-39Q-21
109 P-39Q-20 fitted with a four-bladed Aeroproducts propeller.
RP-39Q-22
12 P-39Q-20s converted to two-seat trainers.
P-39Q-25
Production variant similar to the P-39Q-21 but with a reinforced aft-fuselage and horizontal stabiliser structure; 700 built.
P-39Q-30
Production variant that reverted to the three-bladed propeller; 400 built.
ZF-39
Remaining examples in service, re-designated in June 1948.
P-45
The P-45 was the initial designation of the P-39C or Model 13.
XFL-1 Airabonita
One prototype tail-wheel undercarriage carrier fighter for the USN.
XTDL-1
United States Navy (USN) designation for two P-39Qs used as target drones.
Assigned to NAS Cape May for test work.
Later redesignated F2L-1K.
F2L-1K
XTDL-1 drones re-designated.
P-400
An export model of the P-39 with a less powerful cannon, using a 20 mm Hispano cannon rather than the standard 37 mm cannon.
It also had 2 .50 calibre machine guns in the nose, and 2 x .30 calibre machine guns in each wing.
Airacobra I
Bell Model 13, Royal Air Force (RAF) designation for three P-39Cs delivered to the A&AEE Boscombe Down for testing.
Airacobra IA
Bell Model 14.
Briefly named Caribou.
1,150 hp V-1710-E4 engine, 1 × 20 mm cannon with 60 rounds and 2 × .50 calibre machine guns mounted in the nose and four .303 calibre machine guns were mounted in the wings.
IFF set removed from behind pilot.
*Notice*
The designation IA indicates direct purchase aircraft (as opposed to Lend-Lease); 675 built.
The USAAF operated 128 former RAF aircraft with the designation P-400.
