Airacobra I for RAF, P-400

Last revised August 4, 2010




While the YP-39 and the P-39C were being test-flown, Bell Aircraft began work on an export version of the Airacobra known as the Bell Model 14. It was to be powered by a 1150 hp Allison V-1710-E4 engine which had twelve exhaust stacks on each side rather than the usual six. France was sufficiently interested that they ordered 200 Model 14s on October 8, 1939.

All of the media hype surrounding the spectacular performance of the XP-39 prototype had caught the attention of the British Direct Purchase Commission which had visited the USA in 1940 in search of combat aircraft. Seduced by promises of 400 mph top speed, a tricycle undercarriage, heavy cannon armament, and high climb rates, the British ordered 675 examples of the Airacobra. Unfortunately, Bell's glossy advertising brochures did not distinguish between the performance of a lightly-loaded, unarmed, highly-polished experimental prototype and a production fighter heavily-loaded with military equipment and armament, and the British were to rue the day that they ever looked at an Airacobra.

In 1940, the British were desperate for combat aircraft and were willing to consider just about anything that had wings, irrespective of how poor its performance might be. Consequently, when Bell submitted specifications to the British Direct Purchase Commission for a fighter with a top speed of 400 mph, a ceiling of 36,000 feet, and a range of 1000 miles, the Commission literally salivated on the spot and ordered 675 Bell Model 14s sight unseen on April 13, 1940.

The RAF model was at first named Caribou, but the American name of Airacobra was adopted in July 1941. The British Airacobra was virtually identical to the American P-39D, but the slower-firing 37-mm cannon was replaced with the faster-firing and more reliable Hispano 20-mm cannon with 60 rounds. Two 0.50-inch machine guns were mounted in the fuselage, and four 0.30-inch machine guns were mounted in the wings. The engine of the Model 14 was the 1150 hp Allison V-1710-E4 (-35). The British serials of the Airacobras were AH570/AH739 (170 planes), AP264/AP384 (121 planes), BW100/BW183 (84 planes), and BX135/BX434 (300 planes).

Bell began test flying the first Model 14 Airacobra I in April 1941. It carried the British serial number AH570. Tested on the second British Airacobra (AH571) was a revised rudder of more angular shape and less area. Although the aircraft was delivered to England in this form, this rudder was not adopted as standard. A very small dorsal fin just ahead of the rudder became a standard feature of the RAF Airacobras and was also a distinguishing feature of the American P-39D and subsequent versions.

President Roosevelt signed the Lend-Lease Act on March 11, 1941, permitting large quantities of war supplies to be transferred to the Allies. Among the early requisitions under Lend-Lease were three P-39Cs intended for "war tests" plus a batch of 150 Airacobra IAs--the A suffix being used to distinguish between Lend-Lease and Direct Purchase machines, which were otherwise identical. In the event, only the three P-39Cs were ever delivered as British machines, and were assigned the serials DS173/DS175 (USAAF werials 40-2981, -2983, -2984). The P-39Cs could be distinguished from the British Airacobras by the four machine guns in the nose and the lack of wing guns.

The first of these P-39Cs actually arrived at RAF Colerne on July 3, 1941, followed by the other two the next day. It made its first test flight in England on July 6. However, during trials at Duxford, the performance proved disappointing. Although the test pilots praised the general ease of handling of the aircraft, the maximum speed was a shocking 33 mph lower than that anticipated. The fighter proved to be definitely inferior to the Hurricane and Spitfire in climb rate and ceiling, and the 750-yard takeoff run of the Airacobra excluded its operation from some smaller fighter airfields. There was universal shock and dismay among the RAF personnel. What had gone wrong? Bell Aircraft executives later sheepishly admitted that their performance figures had been based on the unarmed and unequipped XP-39 prototype, which weighed a ton less than the armed and equipped P-39C.

The first British-purchased Airacobras began arriving at Colerne before the end of July, joining the three P-39Cs already there. Deliveries of the Airacobra to Britain had to be made by sea, since the Airacobra lacked the range to make the Atlantic crossing. By the end of September, eleven machines had been received. No. 601 "County of London" Squadron was selected to be the first Fighter Command squadron to equip with the Airacobra.

No. 601 Squadron pilots found numerous flaws and weaknesses during their initial work-up with the the Airacobra. Some of them were a question of improving operational efficiency and pilot comfort, but others were considered essential to make the aircraft operational. Numerous modifications were made in the field in an attempt to make the aircraft suitable for combat. A master valve was introduced to allow oxygen to be turned on from the cockpit. The gunsight was modified to improve forward visibility. Changes to the ammunition tanks for the wing guns were made. Modifications were made to the cockpit harness release in order to simplify the operation. The IFF (Identification, Friend or Foe) set was removed from behind the pilot, where it obstructed aft view. A throttle control quadrant friction damper was introduced.

The Air Fighting Development Unit received a British Airacobra I on July 30. They subjected it to tests and completed their report on September 22. They found the aircraft to be pleasant to fly and easy to takeoff and land. Controls were well balanced and although heavier than those of the Spitfire at normal speeds, did not increase appreciably in weight at high speeds as they did in the Spitfire. It was difficult to hold the aircraft in a dive at high speeds unless the aircraft was trimmed nose-heavy. During a turn, the Airacobra would give ample warning of a high-speed stall by severe vibration of the whole airframe. Handling in formation and formation attacks was good, although deceleration was poor because of the plane's aerodynamic cleanliness. Take-offs and landings in close formation were not considered safe, since there was considerable difficulty in bringing the aircraft back to its original path after a swing.

The Airacobra I was powered by an Allison V-1710-E4 twelve-cylinder V in-line engine rated at 1150 hp for takeoff. Weights were 5462 pounds empty and 7845 pounds normal gross. Maximum speeds were 326 mph at 6000 feet, 343 mph at 10,000 feet, 355 mph at 13, 000 feet, 341 mph at 20,000 feet. Initial climb rate was 2040 feet per minute. With an internal fuel capacity of 100 Imp gal the Airacobra had an endurance of 1 hour 20 minutes at maximum continuous cruising speed at 6000 feet, 1 hour 5 minutes at 12,000 feet, and 1 hour 35 minutes at 20,000 feet. The true airspeeds at these altitudes were 287 mph, 327 mph, and 308 mph, respectively. Under most economical cruise conditions, the endurance increased to 3 hours 20 minutes, the relevant speeds being 183 mph at 6000 feet, 217 mph at 12,000 feet, and 215 mph at 20,000 feet. Under maximum continuous climb conditions, it took 15 minutes to reach 20,000 feet. The operational ceiling was considered to be about 24,000 feet, although there was a marked decrease in performance above 20,000 feet. At the Airacobra's rated altitude of 13,000 feet, it was 18 mph faster than the Spitfire VB. However, the speed fell off rapidly above that height, and the two planes were almost exactly matched at 15,000 feet. At 20,000 feet, the Spitfire VB was 35 mph faster and at 24,000 feet it was 55 mph faster. The ground run of the Airacobra during takeoff was 2250 feet, as compared with 1470 feet for the Hurricane II and 1590 feet for the Spitfire V.

The AFDU also did some comparative dog-fighting tests with the Airacobra against a Spitfire VB and a captured Messerschmitt BF 109E. The Airacobra and the Bf 109E carried out mock dog-fighting at 6000 feet and 15,000 feet. The Bf 109E had a height advantage of 1000 feet in each case. The Bf 109, using the normal German fighter tactics of diving and zooming, could usually only get in a fleeting shot. The Bf 109 could not compete with the Airacobra in a turn, and if the Bf 109 were behind the Airacobra at the start, the latter could usually shake him off and get in a burst before two complete turns were completed. If the Bf 109 were to dive on the Airacobra from above and continue the dive down to ground level after a short burst of fire, it was found that the Airacobra could follow and catch up to the Bf 109 after a dive of over 4000 feet. When fighting the Bf 109E below 20,000 feet, the Airacobra was superior on the same level and in a dive.

A similar trial was carried out against a Spitfire V. Although the Airacobra was faster than the Spitfire up to 15,000 feet, it was outclimbed and out-turned by the Spitfire. Unless it had a height advantage, the Airacobra could not compete with the Spitfire. If on the same level or below, at heights up to about 15,000 feet, the Airacobra would have to rely on its superior level and diving speeds and its ability to take negative "G" without the engine cutting out. Above 15,000 feet, the Airacobra lost its advantage in level speed.

The Airacobra was considered to be very suitable for low altitude operations because of the excellent view and controllability, and it was fully maneuverable at speeds above 160 mph. It was not difficult to fly at night, but the exhaust flames could be seen by another aircraft flying three miles to the rear. The flash from the nose guns was blinding, and could cause the pilot to lose not only his target but also his night vision. Firing of the nose guns caused the buildup of carbon monoxide contamination in the cockpit, and this could reach a lethal level very quickly. The guns were fairly inaccessible, and maintenance was troublesome.

By the end of September, No. 601 Squadron had received permission to take its Airacobras into action. On October 9, two Airacobras took off from RAF Manston and flew across the Channel on a "rhubarb"--a code name for a small-scale raid by fighters against targets of opportunity. On this raid, they shot up an enemy trawler near Gravelines. The next day two Airacobras visited the same area, but found no targets. On October 11, two aircraft flew to Gravelines and Calais and hit some enemy barges and then three Airacobras flew to Ostend, but no targets were found.

After these four missions, the RAF Airacobras were taken off operations because of difficulties encountered with the compass. The compass was too close to the guns in the nose, and when the guns were fired, the compass got thrown out of alignment. Deviations of anything from 7 degrees to 165 degrees were recorded. Without a reliable compass, pilots tend to get themselves lost. In December of 1941, the Airacobra was officially withdrawn from operational service with the RAF.

In spite of the problems with the compass and the need for flame dampers for the exhaust and flash suppressors for the nose guns, the RAF concluded that the Airacobra would make an excellent day fighter at altitudes below 20,000 feet and was well suited for the ground-attack role. However, before these plans could be implemented, a decision was made to divert the bulk of the British Airacobra contract to Russia.

By the time this decision was made, production of British-contract Airacobras had reached four a day at Bell's Buffalo plant. The initial contract for 170 planes (RAF serials AH570 thru AH739) had been completed before the end of September, and all but six of these planes had actually been shipped to Britain. However, many of them remained in their crates and were shipped directly to the Soviet Union without being opened. Somewhere between 80 and 100 Airacobras were assembled and flown in Britain by the end of 1941. They were gathered at maintenance units for final modification before being re-crated and shipped to the Soviet Union during 1942. In all, the Soviet Union received 212 of the British Airacobras (some of them shipped direct from the USA), but 49 more were lost at sea en route.

No 601 Squadron relinquished its 13 Airacobras in March of 1942 in favor of Spitfires. One Airacobra was fitted with an arrester hook and was used for deck landing trials at the RAE at Farnborough.

After Pearl Harbor, the USA found itself in desperate need of aircraft to stem the Japanese onslaught in the Pacific. Consequently, nearly 200 of the British direct-purchase Airacobras still in the USA were promptly requisitioned by the USAAC. Although they were similar to the USAAC's P-39Ds, they were not identical and were known by the USAAC under the non-standard designation of P-400. The P-400 designation had, in fact, been associated with the British Airacobras for contractual purposes as early as August 1941. The USAAC P-400s retained their original British serial numbers and their three-color camouflage paint. Most of these planes were used for training stateside, but some of them were rushed to the Southwest Pacific in an attempt to stem the onrushing Japanese advance.

The P-400s also saw some use closer to Britain. 179 of the Airacobras sent to Britain were re-acquired by the USAAF and were sent to North Africa to join the Twelfth Air Force.

Disposition of RAF Airacobras

AH573 crashed Feb 11, 1942 from Boscombe Down.  Engine failure just after takeoff. Pilot killed.
AH576 in belly landing Aug 29, 1941
AH581 crashed after engine failure Nov 21, 1941.
AH582 crashed during aerobatics Oct 19, 1941.  Pilot killed.
AH596 in forced landing at Colchester Sep 29, 1941.
AH602 crashed during aerobatics Jan 12, 1942.
AH603 crashed on takeoff Dec 12, 1941
AH733 delivered to RAF, but transferred to USSR

Disposition of P-400s

AH728 (c/n 14-159) transferred to USSR.  Reports that it was lost at sea, but other reports have it
	actually having been delivered.  There are reports of this plane being diverted to Austraila 
	and condemed there Sept 3, 1944.
AH735/738
	AH737 not delivered to Britain, To USSR.  There are reports of this plane being diverted to
		Australia Mar 1942, and condemned there Apr 13, 1943.
AP266/268 to USAAF
AP274 to USAAF
AP278 to USAAF
AP280 to USAAF
AP287 to USAAF
AP290 to USAAF
AP291 to USAAF
AP295 to USAAF
AP297 to USAAF
AP300 to USAAF
AP304 to USAAF
AP305 to USAAF
AP319 to USAAF
AP322 to USAAF
AP326/346 to USAAF
AP335 to USAAF.  crashed landed Aug 2, 1943 at Lakekamu River, PNG
AP347 to USAAF.	force landed Aug 20, 1943 at emergency strip with 36th FS of 8th FG.  Retrieved by RAAF Chinook and
			now rests at the Jackson's Airport Pilots Club in a fenced enclosure.
AP348/357 to USAAF
AP359/360 to USAAF
AP361 to USAAF.  Pilot bailed out near 14-Mile Drome PNG Jun 18, 1942.
AP362/383 to USAAF
BW100/105 to USAAF
BW107/108 to USAAF
BW110/117 to USAAF. 
	BW114 was c/n 14-306 and came to Australia Apr 1942 for conversion for RAAF.   Damaged
		Feb 10, 1943, condemned Apr 1, 1944.
BW118 delivered to RAF and returned to USAAF
BW119/130 to USAAF
BW134/148 to USAAF
BW150/168 to USAAF
BW169 to USAAF.   pilot bailed north of Port Moresby PNG Jun 18, 1942.
BW170/183 to USAAF
BX135 to USAAF.  condemned Sep 3, 1944
BX136 to USAAF. condemned Nov 25, 1942
BX137 to USAAF. wrecked at Tontouta AB, New Caledonia Jun 7, 1942
BX138 to USAAF. wrecked at Tontouta AB, New Caledonia Jun 9, 1942
BX139 to USAAF.  condemned Oct 27, 1943
BX140 to USAAF. condemned Sep 3, 1944
BX141 to USAAF wrecked Jan 28, 1942 at Margualo Station.  Pilot bailed out OK.
BX142 to USAAF.  condemned Sep 3, 1944
BX143 to USAAF.  condemned Apr 27, 1943
BX144 to USAAF.  condemned Sep 3, 1944
BX145 to USAAF.   to CL-26 Mar 19, 1942
BX146 to USAAF.  condemned Sep 3, 1944
BX147 to USAAF.  condemned Sep 3, 1944
BX148 to USAAF.  condemned Sep 3, 1944
BX149 to USAAF.  condemned Mar 23, 1943
BX150 to USAAF.  wrecked Jun 8, 1942 at Tontouta AAB, New Caledonia.
BX151 to USAAF.  condemned Nov 25, 1942
BX152 to USAAF.  wrecked Jun 8, 1942 at New Caledonia.
BX153 to USAAF.  condemned Sep 3, 1944
BX154 to USAAF.  condemned Nov 25, 1942.
BX155 to USAAF.  condemned Sep 3, 1944
BX156 to USAAF.  condemned Nov 25, 1942
BX157 to USAAF.  condemned Nov 25, 1942
BX158 to USAAF.  condemned Mar 23, 1942
BX159 to USAAF.  condemned Nov 25, 1942
BX160 to USAAF.  condemned Nov 1, 1942
BX161 to USAAF.  condemned Nov 25, 1942
BX162 to USAAF.  condemned Mar 23, 1943
BX163 to USAAF.  condemned Dec 28, 1942
BX164 to USAAF.  surveyed Jan 24, 1944
BX165 to USAAF.  With 8th Fg, 36th FS, engine cut out and crashlanded short of runway, Durand, NG May 24, 1943.  Condemned May 27, 1943
BX166 to USAAF.  condemned Sep 3, 1944
BX167 (c/n 14-359) to USAAF.  surveyed Jul 14, 1944
BX168 to USAAF.  condemned Oct 27, 1943
BX169 to USAAF.  condemned Sep 3, 1944
BX170 to USAAF.  condemned Aug 30, 1942
BX171 to USAAF.  surveyed in USA Jul 15, 1945
BX172 to USAAF.  to RFC in Cincinatti Feb 10, 1945
BX173  to USAAF.  condemned Sep 3, 1944
BX174 (c/n 14-415) to USAAF.  condemned Nov 23, 1942
BX187 ended up with USAAF in UK in 1942
BX192 to USAAF.  to RFC at Rome, NY Aug 8, 1945
BX204 to USAAF.  off inventory Feb 29, 1944
BX206 to USAAF.  to RFC at Yuma AAF, AZ Mar 20, 1945
BX209 to USAAF.  salvaged Aug 17, 1944
BX210 to USAAF.  to RFC at Yuma AAF, AZ Feb 29, 1945
BX216 to USAAF.  to RFC at Yuma AAF, AZ Apr 4, 1945
BX227 to USAAF.  to RFC at Yuma AAF, Mar 16, 1945
BX245 to USAAF.  to RFC at Rome, NY May 8, 1945
BX247 to USAAF.  off inventory Aug 26, 1944
BX270 to USAAF.  to RFC at Yuma AAF, AZ Feb 29, 1945
BX279 to USAAF.  to RFC at Yuma AAF, AZ Mar 24, 1945
BX290 to USAAF.  condemned Jul 8, 1944
BX302 to USAAF.  Shipped overseas after Oct 1943. Returned to USA Jul 30, 1944.
	To RFC at Rome, NY May 8, 1945.  There is a photo of this aircraft in Soviet AF colors.
BX310 to USAAF.  to Italy Feb 11, 1946
BX320 to USAAF.  crashed May 27, 1944
BX323 to USAAF.  surveyed in USA Mar 2, 1944
BX326 to USAAF.  to RFC at Yuma AAF, AZ Mar 20, 195
BX327 to USAAF.  to RFC at Yuma AAF, AZ 
BX345 to USAAF.  salvaged Jun 12, 1944
BX348 to USAAF.  to RFC at Yuma AAF, AZ Mar 16, 1945
BX409 to USAAF.  to reclamation at Luke AAF, AZ Mar 13, 1946
BX424 to USAAF.  salvaged Nov 9, 1944

Sources:



  1. War Planes of the Second World War, Fighters, Volume Four, William Green, Doubleday, 1964.

  2. The American Fighter, Enzo Anguluci and Peter Bowers, Orion Books, 1987.

  3. United States Military Aircraft since 1909, Gordon Swanborough and Peter M. Bowers, Smithsonian Institution Press, 1989.

  4. P-39 Airacobra in Action, Ernie MCDowell, Squadron/Signal Publications, 1980

  5. The Calamitous 'Cobra, Air Enthusiast, August 1971.

  6. Airacobra Advantage: The Flying Cannon, Rick Mitchell, Pictorial Histories Publishing Company, Missoula, Montana

  7. Airacobra Advantage--The Flying Cannon, Rick Mitchell, Pictorial Histories Publishing Company, 1992

  8. Bell Cobra Variants, Robert F. Dorr, Wings of Fame, Vol 10, AirTime Publishing , Inc., 1998.

  9. E-mail from Gordon Birkett on disposition of AP347, BW169, AP361, plus serial numbers on USAAF P-400s.

  10. E-mail from Terence Geary on P-400 dispositions.

  11. Andrew Thomas, Bell Airacobra In RAF Service, International Air Power Review, Vol 6, 2002

  12. E-mail from Franek Grabowski on AH728, AH733, AH737, BW118, BX302.

  13. E-mail from Nick Jenkins on crash of AH573.

  14. E-mail from Andrew Linden on loss of BX165