Dinger's Aviation Pages

Some thoughts on the rejection of the P39 / P400 Airacobra by the RAF.

The P39 Airacobra is one of those aircraft that is a constant source of discussion, sometimes heated argument, between aviation enthusiasts. How could an aircraft that was particularly liked by the Soviets, be regarded as a failure by the Americans, and be rejected completely by the British RAF after only a few combat sorties? I don't pretend to know the complete answer, I would just highlight some points that are rarely bought up in modern discussions of the type, being largely forgotten.

Lined up for inspection by the press, Airacobras of 601 Squadron at Duxford in August 1941.

On 1st March 1940, an article appeared in the British weekly Aeroplane magazine. It was highly critical of the new Bell P-39 Airacobra and the performance claims made for it. One point the author stressed was that a mid-engined aircraft requires a long extension shaft to the prop. That adds extra weight to the aircraft, weight that is avoided in a traditional front-engined design. So, all things being equal, a properly designed front-engined fighter would always be superior to a mid-engined one because it would not carry the additional weight of the extension shaft. The added weight and complication of the big steerable nose-wheel would only compound the matter. The author also had a particular issue with the location of the carb air intake behind the cockpit, which he asserted would be highly inefficient. The position of the engine behind the pilot was also criticised as in a crash it could "run over” the pilot (this was a particularly British concern reflecting the experience with pusher aircraft such as the FE2B and Vickers Gunbus in the First World War). The tone of the whole article was downright nasty and it ended on a particularly sour note.

“As a serious fighter the Bell is all wrong. We trust the British Purchasing Commission in the USA will not be hoodwinked into placing an order”

The article was anonymous, but no one had any doubts who had written it – the dreaded Charles G Grey, editor of
Jane's All the Worlds Aircraft and founder of the Aeroplane magazine.

It is hard now to realise just what influence the old fool had in Britain at the time. He was the man that had led the campaign to close down the Royal Aircraft Factory during World War One, just as it was about to deliver some very advanced designs and an outstanding engine.¹ The Air Ministry ran scared of him on a number of issues. His pro-German attitude eventually proved too much for the publishers of "The Aeroplane" and he was sacked when war broke out in September 1939. However, he was snapped up as an air correspondent by various newspapers and continued to produce articles and books, including this one about the Airacobra. Grey had some peculiar prejudices and theories about aircraft design, many of which were proved wrong. However, in denigrating the P-39 he did have a valid point, however nastily and disparagingly he made it. The performance figures published by Bell were misleading, having been obtained with a highly polished prototype with all armament, armour and radios removed.

So you can imagine the trepidation of the Air Ministry and RAF when the British Purchasing Committee selected the P-39 for production for the RAF in its modified P-400 "Caribou"² form with a 20 mm cannon instead of a 37 mm cannon. It would only need a letter from some pilot to his MP or to a newspaper complaining of even the slightest problem with the new aircraft to have CG Grey down on them complaining of incompetence in the Air Ministry. When the new aircraft were tested after arrival in the UK and found to have a performance well below that expected, just as CG Grey had prophesied 18 months earlier, you can imagine alarm bells started ringing in the Air Ministry!

The first RAF Airacobra combat mission was on the 9th October 1941, when two took off from Manston and flew to the French coast. They strafed a trawler and German troops on a pier.

The other problem with the P-400 was the timing of its arrival in the UK. In early 1941 there was every expectation that the Luftwaffe would renew their daylight attacks on Britain. When the Battle of Britain had petered out in 1940 combats had been happening at increasing heights. The RAF expected that when the battle was re-joined it would start where it had left off, with combat at increasing altitude and maybe with the Germans using new high-altitude pressurised bombers. This had led to the emergency development of the mark VII and VIII high-altitude versions of the Spitfire and the fitting of the Merlin XX in the Hurricane mark II to give a better high-altitude performance. Again, you can imagine the dismay when the new P-400 arrives on the scene and proves to have a particularly disappointing performance at altitude. Even when the Germans invaded Russia everyone assumed that the Soviets would be defeated in a matter of weeks and that the Germans would resume their attack on the UK in the autumn of 1941 or spring of 1942.

Another issue that came to light during testing was the time it took to turn around the aircraft. During the Battle of Britain, when a Hurricane or Spitfire squadron returned to base after combat they would usually come back in dribs and drabs, a few aircraft at a time. The armourers would work on the machine guns in the wings, and even though they had 8 machine guns the way they were installed made them easy to reload without getting in anyone’s way. While this was going on the fuel could be refilled and oil and coolant topped up. So the turn-around time was remarkably quick and the aircraft was ready for the next scramble in a very short time. Largely because of its mid-engine layout, the P-39/ P-400 took much longer to turn around. With the armament in the nose and awkward to get at, the armourers were in the way of the fuel replenishers. Time to turn-around is a powerful force-multiplier and remained a central feature of RAF thinking into the cold-war (the cannon packs on the Hunter jets being a case in point).

In all, 601 Squadron flew just eight combat sorties in the Airacobra. Early in 1942, they were re-equipped with Spitfires.

The RAF defence structure, based on sector stations each controlling a limited number of squadrons, had been a great success in 1940 but it was also inflexible. All day-fighter squadrons had to be capable of being sent against any incoming force and at whatever height, be they bombers or an enemy fighter sweep (one of the reasons for the withdrawal of the Defiant from the Day-fighter role in 1940). It simply would not have been possible to have some P-39 /P-400 squadrons limited to only low-altitude interceptions, and also taking twice the time to turn around.

So you see, the P-39 was just not suitable for the battle RAF Fighter Command thought it was going to have to fight in 1941 or 1942 once the Germans were through with defeating the Russians. Of course, neither the altitude nor turn-around time matters when you go into offensive operations or if you provide air defence over your front line by flying standing patrols. Then, as the Russians did, you can dictate what altitude you want to fight at and take your time re-arming and refuelling your aircraft ready for the next mission.

So when you add this evaluation to the possibilities of the “CG Grey” issue you can perhaps appreciate why the Air Marshals jumped at the chance to unload the P-400s onto the Soviets!


¹ The RAF8 engine, later developed as the Armstrong Siddeley Jaguar.

² When the P-39/P-400 was first ordered for the RAF it was given the name "Caribou" and the first press releases and aircraft recognition diagrams issued for the type referred to it as such (although an alternative spelling of "Cariboo" was also sometimes used which refers to an area of Canada rather than the animal). By the time it was actually used by the RAF it had reverted to its American name of Airacobra.

PDF copy of the Aeroplane Magazine article of 1st March 1940.

Sources and suggested further reading on the Airacobra.

Airacobra I for the RAF, P-400: An excellent page on Joe Baugher's website <Link here>

Airacobra: Hero of the Soviet Union: An article by Dan Zamansky in issue 30 (January 2020) of The Aviation Historian magazine.

Flying Cannon - Bell's Cobra Family, Part 1: An article by Ken Wixey in Air Enthusiast Magazine, Issue 81, May/June 1999.

Anything To Anywhere: An article In the March 1995 edition of Aeroplane Monthly magazine by Ann Welch, wartime ATA pilot. It covers just one month in her logbook (June 1942), during which, amongst a multitude of other types, she ferried eleven Airacobras. It certainly conveys the suspicion and trepidation felt by British pilots flying the aircraft for the first time.

Zero to Hero: An article in the digital Issue 3 of Wingleader Magazine.

P-39 Airacobra in Action: by Ernie McDowell with illustrations by Don Greer, Number 43 in the Squadron/Signal Aircraft Series. Published in 1980.