Talk:M4 autocannon

Merge
Being that the T9 and M4 are different versions of the same gun, I think a merge is in order.

I added some amplifying information about usage of the 37mm cannon on board PT Boats and JFK using an M3 AT gun on his boat. I obtained this info from interviewing 12 different PT boat veterans from WW2 and restoring PT658 in Portland, OR Jerry (jngilmar) —Preceding unsigned comment added by 134.134.139.71 (talk) 17:42, 16 November 2008 (UTC)

M3 and M4
There is a paragraph here that does not belong: "John F. Kennedy's PT-109 had a US Army M3 37mm Anti-tank Gun installed on the foredeck by removing its wheels and bolting it to a heavy timber (4 in x 4 in) which was attached to the deck. This cannon was installed only days before the mission where PT-109 was lost. In fact, the 4x4 timber was used as a float by Kennedy and crew to keep them together during their swim ashore from the stricken hull, since they had displaced their life raft to make room for the 37mm cannon." It'd be nice to put it here, but the M3 was not the same gun. I'm removing it and moving it to the M3 article.--Nukes4Tots (talk) 00:43, 24 February 2009 (UTC)

M1 and M1A2
Okay, not entirely sure why, but the history of this autocannon is missing. The Browning prototype was built and demonstarted in 1921 and developed into an acceptable weapon by 1928. In 1938, it was standardized for anti-aircraft use as the M1. The M1A2 followed and the Navy and Army Air Force adopted it for shipboard use and aircraft use respectively as the M4 cannon. All of this is missing. Am I missing something or is there any reason not to add this? --Nukes4Tots (talk) 00:43, 24 February 2009 (UTC)

Was it used as an anti-tank weapon?
I was wondering if the M4 was ever used by P-39 and P-63 pilots to try and destroy tanks, especially the Russians on the Eastern Front? There were aircraft that used 37mm anti-tank guns in WWII; such as the Junkers Ju-87 Stuka G1 and G-2 and the Yak-9T. While 37mm is not that powerful when compared to the 76mm, 88mm, and other big guns carried by WWII tanks; a 37mm could knock out a tank if it hit them in a vunerable area, i.e. fuel, turret, or the less-armored back area.204.80.61.110 (talk) 18:46, 27 February 2009 (UTC)Bennett Turk


 * Yes, in fact that was the intent. The standard practice was to dive at the tank.  The weak top armor was no match for a round or two of 37mm.  The Russians bought the bulk of the the P-39's for exactly this reason.  It didn't even need to hit a fuel tank, just pretty much anywhere on top.  --Nukes4Tots (talk) 19:03, 27 February 2009 (UTC)


 * Thank you for this information. I think it should be added to the article. Not everyone reads the discussion page.204.80.61.110 (talk) 21:36, 27 February 2009 (UTC)Bennett Turk

No it wasn't. In "Attack of the Airacobras" by dimitri Loza The myth of the m4 auto cannon in the P-39 as a tank buster is dispelled on the first page. The Russians were not sold or issued armor piercing ammunition for the 37mm cannon, only HE [high explosive]. Loza explains that there has been a mis-interpretation of the term "ground support" from the Russian definition [which means stopping enemy aircraft from attacking Russian Ground troups] to the allied definition of "ground Attack" [Where Russian aircraft would attack troops on the ground]. P-39 and the later P-63 were used exclusively in the air superiority role as air-to-air fighters. The Russian pilots loved the M4 because it provided the fire power to kill an aircraft on one firing pass. Common practice for the Russians was to re-wire P-39 to fire the cannon and machineguns simultaniously, from a single trigger, and to hold fire until "the entire plane filled the windscreen". From such close distances, rate of fire, and trajectory were not a problem. The cannon is misunderstood and often misrepresented. The fact that it wasn't very practical for hitting a small maneuverable aircraft at 800yds, doesn't mean it was ineffective as an air-to-air weapon. there is however no evidence it was ever used as an effective tank buster. —Preceding unsigned comment added by 136.2.1.104 (talk) 19:25, 13 October 2010 (UTC)

--Vsolferi (talk) 19:27, 13 October 2010 (UTC)

M4 cannon page...
(note: Moved from my talk page. --Nukes4Tots (talk) 16:35, 1 June 2009 (UTC) )

You can't reasonably compare machine guns with autocannons in a side-by-side review... the two will NOT compare favorably, regardless of what standard of comparison you are using. You can only compare them to other autocannons, within certain limits, and your needless change eliminates what helps distinguish this autocannon from, say, its German counterpart, the BK 37... The point is, saying that it's a feature only if does not detract from the fact that it is a feature of the cannon's deployment and service record. It was too slow to fire, its muzzle velocity was too low for its effective use at long range, and it tended to jam after preforming tight turns... these are facts, not opinions, and you cannot remove them simply because they don't agree with your interpritation of the wording and/or context of use. Magus732 (talk) 03:32, 1 June 2009 (UTC)


 * I'm confused, you're arguing my point. You can't reasonably compare an autocannon to a machinegun.  When it says, "Too slow" you have to have a comparison.  So, too slow compared to what?  To machineguns?  To other Autocannon?  Demonstrate this.  It was not too slow to be effective against tanks and bombers, the targets it was good at destroying.  --Nukes4Tots (talk) 06:16, 1 June 2009 (UTC)


 * No, I mean it was too slow for aerial combat and from everything I've read, it still jammed a lot, making it useless against anything... Magus732 (talk) 06:22, 1 June 2009 (UTC)


 * From what you've read? What have you read?  Saying the gun is useless against anything is quite the POV statement considering they were the primary armament for the P39 and P63.  You'll have to demonstrate that with equally strong sources. --Nukes4Tots (talk) 06:25, 1 June 2009 (UTC)


 * I don't think you're listening to me... first of all, I said it was only useless in the sense that it tends to jam frequently... unfortunately, the only source I can offer you is an earlier version of this page, so I'm afraid I've already lost that argument... as to the other points I was trying to make, it had a rate of fire of only 150 rounds/min, which is below even the 40 mm Bofors anti-aircraft gun, so, yes, it is too slow for most air-to-air uses... and since the planes carrying it were meant as interceptors and not fighters, I'd say that makes it even more useless, since they fire too slowly to hit most fast-moving targets... Magus732 (talk) 06:30, 1 June 2009 (UTC)


 * First, it didn't jam frequently. Second, the rate of fire and muzzle velocity were comperable to other aircraft-mounted autocannon of the time.  Third, it was designed for use against bombers and tanks.  You can't say that it has less rate of fire than machineguns and that made it ineffective, it was a CANNON.  You can't say it was ineffective against fast-moving targets when it wasn't designed to be.  Find a reference to support your side. --Nukes4Tots (talk) 06:38, 1 June 2009 (UTC)


 * That's all true, yes... but considering the fact that the P-39 didn't just serve on the Eastern Front, and, in fact, suffered quite a bit at the hands of the Zero, I'd say something wasn't working right... if Wildcats with .50 cal machine guns could chop Zeros out of the sky under the right circumstances, and the P-39 was a better overall plane, - in terms of speed, rate of climb (up to about 17,000 ft, of course), and turning radius - then it should have been a one-hit wonder, shouldn't it? Magus732 (talk) 06:45, 1 June 2009 (UTC)

(unindent) You're ignoring my core point, that the previous text was comparing the 37mm Autocannon with heavy machineguns employed agaisnt fighters. You extrapolate that since the P-39 proved ineffective against the Zero, it must be the autocannon's fault. Incorrect. In fact, the Zero was superior to EVERY prewar American fighter and most early war fighters. You can't blame that on the armament, it was maneuverability, handling, and speed. You are incorrect in stating that Wildcats could "cut Zeros out of the sky". P-40's could do that as well. I propose that you've spent too much time reading the statistics and too little time reading actual history. I don't feel that this discussion will go anywhere as it's gone full-circle. I'm going to move it to the M4 page and suggest you find some strong references to back up your strong assertions on the effectiveness of the M4. --Nukes4Tots (talk) 16:33, 1 June 2009 (UTC)


 * I hate to say this, but, you're right... I have spent too little time gathering history on this matter... unfortunately, I can't find anything substantial on the subject except websites with dubious reference value... however, I do know for a fact that the Zero's thin armor plating and lack of self-sealing fuel tanks made it fairly vunerable to the Wildcat's machine guns, and it was easy to shoot down if one could keep the Zero in one's gunsights, which was generally very difficult to do (although this can be said of practically every Allied fighter of the period)... and as to the Zero's dominance: yes, it did dominate virtually everything on the battlefield until the Hellcat and Corsair... however, it was not invincible... Wildcats and P-40s, when handled well enough, did beat the Zero early in the war... in theory, it means that the P-39 - with its cannon - could do the same... that was the point I was trying to make... of course, I realize that opinions and theories don't mean jack on Wikipedia, so I submit to your knowledge of this subject... I'll leave the page as it is... Magus732 (talk) 18:08, 1 June 2009 (UTC)


 * Well, at least we agree that the 37mm M4 cannon has a low rate of fire and low muzzle velocity when compared to machineguns. You'd KINDA have to know my background, but in a previous life I boresighted and calibrated Autocannons for Aircraft (A-10) and am somewhat of an Aircraft Armament expert of sorts. We still use the BOFORS 40mm with a lower rate of fire but higher muzzle velocity. It really brings it into prespective when you have the shells side-by-side as I used to (back in the day) as to how similar they were back then.  We don't disagree on the salient features of the cannon, I just don't believe there is any reason for the unsupported POV and unfair comparrison in the lede. --Nukes4Tots (talk) 03:54, 2 June 2009 (UTC)


 * So, Nukes, your version of the lede reads "It was a compact design with a relatively low muzzle velocity and rate of fire." You have been harping on the subject of "relative to what" but here you are saying "relatively low" regarding muzzle speed and rpm. You also continue to say that the gun could shoot down a bomber with as little as one hit, though you've taken out the word "guaranteed". What good is that change when the "one hit" bit is left in? You removed the words "It was designed to provide interceptors with" and replaced them with "It provided interceptors with"... What was the thought behind this edit? That the gun was designed with an optimistic view to its effectiveness cant be in doubt. You removed that part. The gun did not actually provide interceptors with all the things that were anticipated, because it was too s-l-o-w for air combat and it was prone to jamming after any kind of violent air maneuver of the sort normally expected in air combat. It was a dog of a weapon—it didn't work in the air. What's needed here aren't inconsequential edits bounced back and forth between different versions of unsourced text; we need sources! I thought I had a book or two with some statement made by USAAC/USAAF/USAF officer Benjamin S. Kelsey regarding this weapon but I can't find it at the moment. Let's all cool off and start hunting for references. Binksternet (talk) 04:31, 2 June 2009 (UTC)


 * I'm posting here in response to a message on my Talk page. I don't think there's much that needs to be said here, beyond the obvious: The lead paragraph should be a concise summary of the article text, so any description on the cannon ought to be based on what's in the body of the article - and that ought to be sourced. In the absence of sourcing, it is probably better to say less, rather than more, particularly when it comes to offering comparisons or evaluations of the subject.  S HEFFIELD S TEEL TALK 13:09, 2 June 2009 (UTC)


 * I'm sorry, both Bink and Shef, you are here because you were "summoned" by an editor who, if you've read the discussion, made arguments he could not support. I'm not here for the content, per se, I'm here to ensure that the content is supportable.  I made a quick, POV-killing edit here: .  Now you two come here because Magus is trying to support unsupportable words? "Guaranteed to destroy any bomber with as little as one hit" is an unsupportable statement.  "Guaranteed" and "Little as" cannot exist in the same sentence. "Very low" was an unsupported and untrue description of the rate of fire... a rate of fire comperable to other autocannons of the time. "Rapidly drooping arc" is not a common term nor one that is applicable to anythig but spitwads.  If supported, one might say, "curved trajectory" but WTF is a "droopin arc?" I am opposed to "crying to mommy when daddy says no" in general and think this discussion has ended.  I'll carry Magus' commetns from your talk pages here so their content can remain visible to all. Note that Magus is acusing me of bypassing rules and regulations, attacking his credibility, and behaving unprofessionally.  And I'm attackin his credibility?:


 * "User Nukes4Tots is attempting to bypass rules and regulations by attacking my credibility... he has changed a page in the military history section of the site, and he and I have argued back and forth as to the merit of his edit, and instead of behaving profesionally, he has clamied that I'm edit warring with him because I pointed out that his edit needed referencing... I really need help with this guy... this -> <- is what I mean... "


 * "Normally, I would only involve an administrator as a last resort, but I'm afraid I've reached it... in a series of revisions and counter-revisions of the M4 cannon page, Nukes4Tots and I have reached a point of impasse with regard to the page itself... I'm afraid that his actions (and to some extent, my own) are harming the page, and that is why I'm asking for your help as an administrator to sort out my dilemma... this user has continually refused to leave the page alone, despite the facts that his edits are unsourced... I hope that a resolution is available that can prevent any further harmto the page's contents, and I thank you for any advice on this matter that you can provide... you can find what I'm talking about here -> "


 * Really, if you agree with this guy, FIND A REFERENCE to back up terms like "droopin arc". I'd like to see anybody Guarantee me that a bomber can be destroyed with one hit.  That's what we're talking about here.--Nukes4Tots (talk) 15:08, 2 June 2009 (UTC)
 * Magus made this discussion known to me, but I'm no meat puppet. I believe this article is in dire need of references, a point that it seems we all agree on. Absent references, an edit war doesn't appear supportable. Why battle over text that has no reliable source on either side of the debate? Binksternet (talk) 15:44, 2 June 2009 (UTC)

Disregarding the off-topic discussions comparing various other aircraft or (especially the actual operational use, rather than objective technical merit), the T9/M4 cannon had the for primary limitations in performance as an aircraft weapon: it was heavy, slow firing, relatively low velocity, and had a limited ammunition capacity. It was this combination of factors that made it mediocre, as avoiding any one of those problems (let alone multiple ones) would have given it a good deal more overall merit. The low velocity compared to the 20 mm hispano and both .50 and .30-06 Browning machine guns (not to mention the better ballistic shape of the latter two) was notable but also the least critical issue in terms of objective performance for a cannon firing HE projectiles. The trajectory was a mismatch for the high velocity weapons it was mated with on the P-39, but this is also true of the MG FF and MK 108 combined with cannons and/or machine guns of higher velocity as was common in German service, as well as various combinations of cannons used by the Japanese.

140-160 RPM was very low for an aircraft autocannon to be practically used in any caliber and really made the weapon more realistically used as semi-automatic (which also better matched to its limited ammunition supply) but this was neither ideal nor standard procedure. But the bottom line really is that the US should have been capable of engineering a weapon using similar projectiles with better all around performance relative to weight/bulk (higher velocity and/or rate of fire for the same weight), or simply using smaller caliber projectiles as was really more desirable and indeed was the US Army's aim with their .90 caliber (23 mm) cannon projects. (Japanese developments showed the potential of the basic M1917 Browning Short Recoil mechanism to 20, 30, and 37 mm rather than stopping at .50 caliber as the US did, but the US Army apparently rejected all proposals for further scaled up implementations of that mechanism, including one proposal in their .90 cal cannon program)

However, it should at least be noted that the M4 cannon was more reliable than the American M1 and M2 Hispano cannons. These had issues with the chamber size and firing pin length being mismatched with the ammunition on top of apparently lax manufacturing tolerances (and refusal to copy British modifications of the weapon). Regardless of the reason, it could not be used reliably in US service without a re-cocking mechanism accessible to the pilot (as the P-38 used) or excessive amounts of grease and wax applied to the ammunition (apparently causing a snug enough fit for a reliable primer strike) as the US Navy used. The P-39 (or P-400) only used the Hispano briefly and I believe only in its drum-fed M1 form with a 60 round magazine capacity. For whatever reason later P-39 (and P-63) variants didn't employ the M2 Hipano and don't even appear to have tested it experimentally.

For comparison of other larger than 20 mm caliber autocannons, the 23 mm Madsen cannon the US showed some pre-war interest in was belt-fed and capable of a 360 RPM cyclic rate with a typical muzzle velocity of 720 m/s while weighing 53 kg. (less than most war-time variants of the Hispano and slightly more than half that of the M4) See: http://s120.photobucket.com/user/aoe276/media/23Madsen.jpg.html http://www.dws-xip.pl/encyklopedia/lotdz23-dk/ — Preceding unsigned comment added by Kool kitty89 (talk • contribs) 23:29, 7 June 2016 (UTC)

As to the Jamming issue. The P39 article cites McDowell 1980, p. 10. 75.143.19.122 (talk) 18:23, 13 November 2021 (UTC)

YFM-1 Airacuda first
Why is there no mention of the weapon's use in the YFM-1 Airacuda? Binksternet (talk) 16:20, 2 June 2009 (UTC)

M4 as an air to air weapon
According to Birch Matthews book on the development of the P-39 and P-63 [Cobra! The bell aircraft Corperation 1934-1946], the original concept of the development of an "interceptor" by the US army air corps in the 1930s was to combat the threat of large long range bombers. The U.S. was developing heavy long range bombers like the B-17. They were integral to the strategic thinking of the time, and so the Air Corps worked under the assumption that similar weapons were being developed by other nations, and conceived the need for a new "interceptor" to climb fast and high to intercept incoming bombers. It was thought that a cannon was needed to have the fire power to down a large heavy bomber. The P-39 was designed with the M4 for that purpose. It was also equipped with four .30 caliber, and two .50 caliber machine guns, which were no doubt for use against smaller, faster, maneuvering aircraft.

These two roles are important to the discussion of the effectiveness of the M4 in air to air combat. In Dog fighting scenarios where a P-39 would be employing aggressive air combat maneuvers against a A6M Zero or Bf-109 it was certainly true that the fire rate and trajectory of the 37mm M4 would have made it an ineffective weapon. But again formations of 'Bettys' or Ju-88s, or Me-110s, on straight bombing runs the M4 would have been performing the role it was designed for.

In "Attack of the Airacobras" [Dmitriy Loza], a cronicles of the use of the Bell P-39 and P-63 by the soviet air force against the Germans, are numerous statements of love for the 37mm cannon and it's ability to "wreck a plane with a single shot". It is worth noting that description of Russian encounters with German aircraft follow the paradigm of the use for the M4 as a weapon for use against non-maneuvering targets. Most encounters were typically of the ambush type, where firing the weapons was held until very close range. The Russians pilots would dive to very high speed on German formations, and make a single pass and egress [boom and Zoom]. The Russian pilots appreciated the Cobra's 'devastating' firepower which enabled them to destroy the target bandit in a single pass. It is also clear that fighters and Bombers were attacked in this manner.

Russian air to air tactics were very poor at the outset of the war. The use of the American Airacobras changed almost everything about the way the Russians fought the air war against the Germans. Prior to the Airacobra, many Russians planes were not even equipped with radios ["Attack of the Airacobras" (Dmitriy Loza) page reference needed]. The radios in Airacobras allowed coordination of the aircraft by both ground stations, and flight leaders in the air. As a results new tactics evolved quickly in cobra equipped air wings. It is clear that the tactics developed by Russian pilots suited the effectiveness of the M4 as an air to air weapon.

Whether the M4 was an effective weapon, from an historical perspective, may have more to do with the mix of enemy aircraft the cannon came up against than anything else. The threat of large numbers of heavy bomber formations, that the cannon was employed on Airacobras to combat, was something that the allies never really had to face in the war. Conversely, the allies deployed such bombers by the tens of thousands against the Germans, and the response by the Germans was to fit large caliber cannons [30mm mk108] similar to the M4 to the later variants of the bF-109, and FW-190, while making four of them the exclusive weapons on the me-262.

I think one can conclude that large caliber auto-cannons like the M4 were effective against large, non-maneuvering planes like bombers, but were not well suited for air to air combat involving agressively maneuvering targets such as other fighter aircraft.

Vsolferi (talk) 18:58, 10 August 2010 (UTC)


 * Your first two paragraphs are founded on a mistaken belief. At the Benjamin S. Kelsey article you can read that Kelsey, who was the only person in the U.S. who decided on what fighter aircraft the Army would buy, and what characteristics they would have, was working under a prohibition against having heavy weaponry in a fighter, because the heavy bombers were supposed to be self-defending. Standard thought in the U.S. Army Air Corps at that time was that no aircraft design should interfere with the concept of having huge self-defending bomber fleets. Drop tanks and heavy weapons were not allowed on fighters. Kelsey and Gordon P. Saville thought that this was ridiculous, and they worked to increase the punch of the fighters so that they could fight better against whatever enemy was in front of them, including other fighters, enemy bombers, etc. The improvements they imagined would yield a better fighter overall, not a specific design to fly only against bombers. Kelsey and Saville invented (for the USAAC) the term "interceptor" so that the higher-ups would approve the much heavier armament.


 * Kelsey and Saville laid out two aircraft specifications which resulted in the P-38 and the P-39. Both specs required cannon and allowed for machine guns. In battle, the use of each type of gun was of course a tactical decision made by the pilot: if an enemy fighter could be expected to fly through a point in the sky, a gun could be fired into that point ahead of the fighter's path. The slow-firing cannon might be used for a more predictable situation, if the pilot chose, but machine gun rounds could also be used. On the other hand, the indiscriminate spraying of machine gun rounds was not always the answer if the enemy was performing violent evasive maneuvers—if the pilot thought determined that his enemy was heading somewhere, the cannon could be fired into that spot. Basically, both cannon and machine guns must be led correctly to put the rounds on target; they are simply different in their lead. Binksternet (talk) 20:14, 13 October 2010 (UTC)

It is not at all clear what mistaken beliefs you think the first two paragraphs are based on. The logic you present, that heavy weapons were not allowed on fighters because Bombers were self defending, makes no sense because the heavy weapons were not deployed to protect bombers, they were employed to shoot them down. In the American Lexicon, Fighters and persuit planes were designed to destroy enemy fighters. In this role a plane is best armed with multiple weapons of high fire rate to give the pilot a greater statistical chance of scoring hits on a small, fast, maneuvering aircraft. The term "interceptor" was used to describe the roll of climbing to intercept a bomber and knock it out of the sky before it could drop it's bombs. The fledgeling Bell aircraft company was trying to hedge it's bets and cover the fighter/persuit/interceptor roles with a single aircraft. You are correct that at the time there seemed to be much debate about the requirements for a fighter/persuit/intercepter aircraft, and Bell was trying to cover all bases. --136.2.1.104 (talk) 16:14, 20 December 2010 (UTC). --136.2.1.104 (talk) 15:38, 18 October 2010 (UTC)


 * Bell was not hedging its bets. Bell was satisfying an Air Corps specification to the letter. They put a big cannon in the plane as required and filled out the rest of the armament weight requirement with fast-firing machine guns. If the aircraft performed well in the air, it was going to win the Army contract. Binksternet (talk) 22:30, 20 December 2010 (UTC)

"Satisfying the specification to the letter" is a bit of a missrepresentation of the process. The army didn't issue a pre-specification for someone to design a fighter with a 37mm cannon in it. Bell chose to design it into his airplane because he felt it was an impressive weapon and would make his plane more desireable to the Army because it had big firepower for downing large bombers [interceptor role] and for ground attack. It was Bell who chose the 37mm cannon to arm his planes with. After evaluation of the aircraft prototype, The Army liked the idea of the Cannon and so the specifications of the contract included the 37mm Cannon. So of course there is eventually a specification that requires the cannon to be n the plane, but it's because Bell sold the army on the 37mm cannon in an interceptor, not because the army originally wrote a specification for an interceptor with a 37mm cannon in it. --Vsolferi (talk) 15:39, 22 July 2011 (UTC)-vsolferi — Preceding unsigned comment added by 136.1.1.105 (talk) 15:36, 22 July 2011 (UTC)


 * Sorry but no, your chronology is wrong. The specification that Kelsey and Saville sent out in February 1937 was for a fighter that had 1,000 lb (454 kg) of armament, a maximum airspeed of at least 360 mph (580 km/h) at altitude, and a climb to 20,000 ft (6,100 m) within six minutes. The specs, called Circular Proposal X-608 and X-609, gave extra points for a design with tricycle landing gear. Proposal X-608 was for a twin-engine fighter, and X-609 was for a single engine fighter—both proposals required the use of Allison V-1710 engines with turbo-supercharging. Kelsey sent these specs out to a bunch of aircraft designers including Bell, Lockheed, Vultee, Curtiss and others. Kelsey and Saville specified a 25mm Hotchkiss autocannon but it was not ready. When Bell read the proposal they knew the 25mm gun did not exist, and they knew that there were not many choices for a good autocannon. It was then that Bell determined that a 37mm cannon would be their first option. In the late 1930s, the USA did not have a useful autocannon for aircraft, and it was only after much experimentation and testing that the 20mm Hispano emerged as the most reliable. The Lockheed XP-38 gondola mock-up was given an initial 23mm (90 caliber) autocannon, then a 37mm Browning/Colt, demonstrating the unsettled nature of the question, 'Which cannon was best'.
 * You are correct that Bell selected the 37mm cannon. You are wrong in thinking that the 37mm was intended for use against ground targets. The only consideration given by Kelsey and Saville in their specs was to have a couple of air-to-air fighters with more powerful armament.
 * All of this information comes from Warren M. Bodie, engineer, aviation historian and author. Binksternet (talk) 16:33, 22 July 2011 (UTC)


 * The poor dogfighting quality of the 37mm M4 autocannon as described in the Birch Matthews book is true. It tended to jam under high gee forces. However, smaller autocannons were very often used in dogfighting, notably by the Japanese Mitsubishi Zero which had two 20mm cannon, one per wing, and two or four MGs. The Zero was excellent as a twisting, turning fighter. Its pilots were trained to choose between machine gun rounds and cannon rounds as appropriate. The cannon was usually saved for direct shots rather than deflection shots. A cannon shot was often preceded by the pilot shooting some MG tracer rounds to line up the more important cannon shot. Yes, the cannon was nicely suited to ambush, surprise and energy tactics—to "zoom and boom" tactics—but the smaller calibers were also used at times in a tight fight. The Kawanishi N1K "George" fighter had four 20mm cannon, no MGs. Kaneyoshi Muto used his George to make multiple kills in a low level twisting dogfight on 16 February 1945. Binksternet (talk) 17:10, 22 July 2011 (UTC)

The jamming issue is one that is tough to quantify, but it was a factor in the gun's reputation, true. The disscussion of the cannons of other calibers is a bit of a tangent, but I'll comment on it: The effectiveness of those weapons is not in question, as they were very effective in the air-to-air role, but they do not offer insight or provide evidence for the effectiveness of the 37mm in Air-to-air combat. Also I am not incorrect in stating the 37 would also [meaning "secondarily"] be used in the ground attack role. In fact Armor peircing ammunition was part of the plane's weapon load-out options [Except for Russian Airacobras]. I think we have reached the point of agreement that while the Army's general specification asked for a cannon, it didn't specify the 37mm cannon. Bell chose the 37mm. Why he chose that cannon and, how well it worked was the topic of the discussion. My previous posts explain what I believe drove Bell to that choice: Big gun for attacking Big planes, small guns for attacking small planes. --136.1.1.104 (talk) 19:05, 5 August 2011 (UTC)


 * Yes, I think we agree. Binksternet (talk) 21:59, 5 August 2011 (UTC)


 * All the references I've come across that actually bother to try and analyze the jamming problems point to it being a problem with the P-39's ejection ammunition case chutes being too narrow and failing to eject the spent cases. This was supposedly solved fairly early in the P-39's lifetime, but was a problem on some P-39Ds. (which is likely responsible for most comments on problems in US service) — Preceding unsigned comment added by Kool kitty89 (talk • contribs) 23:36, 7 June 2016 (UTC)

M9 autocannon uses
I'm not too wikipedia savvy but if someone wants to find additional sources, there seem to be some experimental aircraft uses for the M9. In particular, the experimental P-63D-1 (production: 1) seems to have used an M9, and this one Russian webpage  shows an A-20 and XA-41 as well.

96.238.86.112 (talk) 07:58, 10 February 2017 (UTC)

Other Manufacturers
In the Aircobra article this is listed as an Oldsmobile T9 Cannon. Obviously someone had data stating that Oldsmobile was also a manufacturer of this weapon. It would be nice if there was a concurrance of information. 75.143.19.122 (talk) 18:18, 13 November 2021 (UTC)