Why did US fighters not use cannon in WW2?
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So it really boils down to two major points:
1. Logistics/commonality. It was easy to mass produce large numbers of .50 BMG quickly, and provide lots of ammo for those guns which were common to lots of other vehicles, to include a dozen or more on every B-17 and B-24 bomber, plus the numerous guns on B-20, B-25, B-26, etc etc., And it was easy to get all those guns and all that ammo from the USA to the far end of the Atlantic and the Pacific. This was essentially the same reason that US tanks used gasoline engines rather than diesel. Despite the far greater fire danger posed by gasoline, it simplified logistics by having a single type of fuel for everything from light jeeps to heavy tanks.
2. Good enough. The targets being shot at were light enough that a .50 BMG did the job. Neither the Germans nor the Japanese had large bombers that needed to be shot down. The exceptions of cannons on US aircraft was for air to ground use, not air to air. And even then, large numbers of .50 BMG rounds on a truck or other ground vehicle (even armored ones) were effective at disabling them even if they did not destroy them. And often disabling was all that was needed. So the crew flying them usually preferred the machine gun equipped aircraft over the cannon equipped aircraft.
There is a third lesser point. Both the AN/M2 (the lightweight aviation version of the ubiquitous "Ma Deuce") and its ammo was relatively small and compared to cannon, very light. Both are very important considerations in a fighter.
1. Logistics/commonality. It was easy to mass produce large numbers of .50 BMG quickly, and provide lots of ammo for those guns which were common to lots of other vehicles, to include a dozen or more on every B-17 and B-24 bomber, plus the numerous guns on B-20, B-25, B-26, etc etc., And it was easy to get all those guns and all that ammo from the USA to the far end of the Atlantic and the Pacific. This was essentially the same reason that US tanks used gasoline engines rather than diesel. Despite the far greater fire danger posed by gasoline, it simplified logistics by having a single type of fuel for everything from light jeeps to heavy tanks.
2. Good enough. The targets being shot at were light enough that a .50 BMG did the job. Neither the Germans nor the Japanese had large bombers that needed to be shot down. The exceptions of cannons on US aircraft was for air to ground use, not air to air. And even then, large numbers of .50 BMG rounds on a truck or other ground vehicle (even armored ones) were effective at disabling them even if they did not destroy them. And often disabling was all that was needed. So the crew flying them usually preferred the machine gun equipped aircraft over the cannon equipped aircraft.
There is a third lesser point. Both the AN/M2 (the lightweight aviation version of the ubiquitous "Ma Deuce") and its ammo was relatively small and compared to cannon, very light. Both are very important considerations in a fighter.
Last edited by KenV; 1st Mar 2018 at 14:22.
I recall reading that Capt Eric "Winkle" Brown shot down 2 FW 200 Condor whilst flying the Grumman Martlett (Wildcat) from HMS Audacity. Thus the .50 cal ammunition was effective against a large 4 engined aircraft. Although the Sea Hurricane with only 8 .303cal mg did manage to down 3 FW 200 Condors, there were a number of occasions when they were unable to inflict sufficient damage to shoot them down.
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The FW 200 was a minimally altered airliner that had serious issues with both fuselage and wing strength - the literature is full of pictures of them falling apart (literally) on landing or taxying. So not the worlds toughest target
IIRC two of the toughest were flying boats - the Sunderland and the Kawanisi 8K "Emily" could take an outstanding amount of punishment apparently
IIRC two of the toughest were flying boats - the Sunderland and the Kawanisi 8K "Emily" could take an outstanding amount of punishment apparently
Ken. WW2, most German and British tanks also used gasoline.
As far as fighter use of Cannon goes, the Germans had quite a lead in the availability and the installation of cannon type weapons. They seem to have appreciated the advantages of the larger calibre well before the RAF and had the 20mm weapons in the wings of the Bf109E before WW2, having learned the lessons in Spain. The RAF seemed to agonise about cannon and the Spitfire had to wait till Nov '40 for the Mk1b to get 20mm cannon in the wings working satisfactorily, while the Luftwaffe outgunned them through the BoB. By the time of the Spit Vb, the Germans had sorted the engine mounted cannon in the 109F and, shortly after, the Fw190 with at least two wing root mounted 20mm, sometimes four and, nothing below 12.7mm. The Germans preferred the bigger weapons and soon moved on to the 30mm MK108. This weapon suffered from early poor quality but did become reliable enough and, with the thincase "minen" type blast shells they were a very effective weapon, only an average of 4 hits req'd to down a heavy bomber. For the Americans, it would seem that the .5 BMG was sufficient to deal with many situations, particularly against fighters and small bombers. Certainly, there was an element of strength in numbers, with 6x .5BMG and generally huge numbers of P51's hunting the Jagdwaffe in the later stages of the War. However, the pure effective weight of fire from the 4xMK108 in a 262 was impressive. Interestingly, the late developed MG213 20mm and MK213 30mm revolver cannon were the basis of many postwar weapons, including the ADEN 30mm and latterly, the Mauser 27mm in the Tornado. Of course, the Americans developed some excellent revolving barrel weapons. However, the instantaneous rate of fire achieved by the revolver type Mauser can be an advantage in a .5sec snap burst and, the installed weight of the Mauser is low.
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As far as fighter use of Cannon goes, the Germans had quite a lead in the availability and the installation of cannon type weapons. They seem to have appreciated the advantages of the larger calibre well before the RAF and had the 20mm weapons in the wings of the Bf109E before WW2, having learned the lessons in Spain. The RAF seemed to agonise about cannon and the Spitfire had to wait till Nov '40 for the Mk1b to get 20mm cannon in the wings working satisfactorily, while the Luftwaffe outgunned them through the BoB. By the time of the Spit Vb, the Germans had sorted the engine mounted cannon in the 109F and, shortly after, the Fw190 with at least two wing root mounted 20mm, sometimes four and, nothing below 12.7mm. The Germans preferred the bigger weapons and soon moved on to the 30mm MK108. This weapon suffered from early poor quality but did become reliable enough and, with the thincase "minen" type blast shells they were a very effective weapon, only an average of 4 hits req'd to down a heavy bomber. For the Americans, it would seem that the .5 BMG was sufficient to deal with many situations, particularly against fighters and small bombers. Certainly, there was an element of strength in numbers, with 6x .5BMG and generally huge numbers of P51's hunting the Jagdwaffe in the later stages of the War. However, the pure effective weight of fire from the 4xMK108 in a 262 was impressive. Interestingly, the late developed MG213 20mm and MK213 30mm revolver cannon were the basis of many postwar weapons, including the ADEN 30mm and latterly, the Mauser 27mm in the Tornado. Of course, the Americans developed some excellent revolving barrel weapons. However, the instantaneous rate of fire achieved by the revolver type Mauser can be an advantage in a .5sec snap burst and, the installed weight of the Mauser is low.
OAP
Last edited by Onceapilot; 1st Mar 2018 at 19:50. Reason: Correct Spitfire equipped cannon intro
Six or Eight .50 Caliber machine-guns focused at a point some several hundred yards in front of the aircraft put a lot of Rounds in a very small area.
There is no comparison between a .50 caliber round and a .30 caliber for effect.
The Spit with four 20MM cannon must have been a distinct improvement over the .303 equipped versions.
There is no comparison between a .50 caliber round and a .30 caliber for effect.
The Spit with four 20MM cannon must have been a distinct improvement over the .303 equipped versions.
I recall reading that Capt Eric "Winkle" Brown shot down 2 FW 200 Condor whilst flying the Grumman Martlett (Wildcat) from HMS Audacity. Thus the .50 cal ammunition was effective against a large 4 engined aircraft. Although the Sea Hurricane with only 8 .303cal mg did manage to down 3 FW 200 Condors, there were a number of occasions when they were unable to inflict sufficient damage to shoot them down.
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There was also a Hurricane at North Weald called the 'old cow' (IIRC) with 20mm cannon ,that was somewhat slower @300mph than the Browning armed ones. It has been suggested by numerous BoB pilots, that had cannon fighters been more available, the outcome would have been even more decisive.
Not quite correct I am afraid. 19 Squadron had Spitfire Mk1bs with cannon in May/June 1940, but suffered from problems with their operation. I remember reading somewhere years ago that a pilot fired on a ME 109 ( and I am sure this was over Dunkirk) and immediately the windscreen of his Spit turned red!
There was also a Hurricane at North Weald called the 'old cow' (IIRC) with 20mm cannon ,that was somewhat slower @300mph than the Browning armed ones. It has been suggested by numerous BoB pilots, that had cannon fighters been more available, the outcome would have been even more decisive.
There was also a Hurricane at North Weald called the 'old cow' (IIRC) with 20mm cannon ,that was somewhat slower @300mph than the Browning armed ones. It has been suggested by numerous BoB pilots, that had cannon fighters been more available, the outcome would have been even more decisive.
OAP
I think this is the wrong way round:
Rather than the USAAF to cannon, the RAF should have gone for 0.50 cal.
We all know the 0.303 is too light and 20mm too slow and low rate of fire for A2A.
Carrying both didn't make up for the deficiencies of the other!
Rather than the USAAF to cannon, the RAF should have gone for 0.50 cal.
We all know the 0.303 is too light and 20mm too slow and low rate of fire for A2A.
Carrying both didn't make up for the deficiencies of the other!
Cannon were thought about pre WW2, but ditched for .303. The 8 gun fighter was a potent weapon when thought of in the mid 30s. The idea was even toyed with 10 or 12 guns. I believe tests were carried out pre war on .5s, but the results were disappointing.
Interestingly, reading about the Hispano-Suiza 20mm cannon development, it seems that the weapon development in the USA was never satisfactory during wartime and so, the continued use of the .5 Browning was something of a force-majeure.
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I think it was recognized that they needed something bigger than the 0.50 cal HMG. The USN held a "Joint Fighter Convention" in 1944 and the moderator told the attending aircraft companies that they should provide room in their designs for the oncoming T17E3 .60 cal Aircraft MG. It was pretty impressive gun, had a very high muzzle velocity but never made it to use. Some large production contracts were canceled.
This link will provide you with more than you probably want to know about the T17E3 .60 Cal MG. Just scroll down on the posts.
https://www.milsurps.com/showthread.php?t=32509
This link will provide you with more than you probably want to know about the T17E3 .60 Cal MG. Just scroll down on the posts.
https://www.milsurps.com/showthread.php?t=32509
Last edited by tonytales; 2nd Mar 2018 at 20:34. Reason: corrected mispelling
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The simple fact of life of cannon v machinegun is quite simply that the increased size of the cannon round allows the incorporation of high explosive charges, complex fuses and incendiary components. Late in the WWII the RAF carried out extensive evaluations of the effectiveness of many different calibres and types of ammunition. The result was that the 20mm Hispano semi-amour piercing incendiary round was by far the most effective round in aerial combat. It was also very good when used for strafing and was quite capable of penetrating the upper armour of the Panzer Mk4.
Subsequently in the Korean war it was established that .5" Browning ammo. used by the F86 Sabre was being deflected by the airflow over the wings and fuselage of the Mig 15 once speeds got up to round Mach .85. It was established that this was largely due to the light weight of the .5 cal. bullets.
Subsequently in the Korean war it was established that .5" Browning ammo. used by the F86 Sabre was being deflected by the airflow over the wings and fuselage of the Mig 15 once speeds got up to round Mach .85. It was established that this was largely due to the light weight of the .5 cal. bullets.
As others have noted, the US fighters didn't often face heavy bombers in either the European or Pacific Theaters, and the 50 cal. did the job quite well on the smaller aircraft (especially the Japanese which lacked defensive armor and such).
My dad fought in the South Pacific - Guadalcanal, New Guinea, Philippines. By the time he got to Guadalcanal in late 1942 the P-39 was pretty much outclassed for air-to-air, but was very effective for air to ground with that big cannon in the nose (TBM - I thought all the P-39s had 37mm cannon but perhaps some used the 20mm). According to my dad, when the P-39 fired that 37mm cannon during a strafing run, he could see the aircraft 'stutter' from the recoil. If his observation was correct, I can't help but think that firing that big cannon during a dog fight would make aircraft control very tricky. Further, for air-to-air, mixing (relatively) slow cannon with higher speed 50 cal. would make leading the target for both nearly impossible.
The picture that Just This Once posted helps, but it is hard to appreciate how big a 50 cal round really is if you haven't seen one. I have a bottle opener made out of an inert 50 cal round and it is HUGE!
My dad fought in the South Pacific - Guadalcanal, New Guinea, Philippines. By the time he got to Guadalcanal in late 1942 the P-39 was pretty much outclassed for air-to-air, but was very effective for air to ground with that big cannon in the nose (TBM - I thought all the P-39s had 37mm cannon but perhaps some used the 20mm). According to my dad, when the P-39 fired that 37mm cannon during a strafing run, he could see the aircraft 'stutter' from the recoil. If his observation was correct, I can't help but think that firing that big cannon during a dog fight would make aircraft control very tricky. Further, for air-to-air, mixing (relatively) slow cannon with higher speed 50 cal. would make leading the target for both nearly impossible.
The picture that Just This Once posted helps, but it is hard to appreciate how big a 50 cal round really is if you haven't seen one. I have a bottle opener made out of an inert 50 cal round and it is HUGE!
Cheers
OAP
The Hurricane IIB entered squadron service with 12x .303s I think? Although the IIC and IID appear to have been more successful, albeit mainly air to ground.