WWII Tactical AAA

[Tony Williams]

As for hitting power, two comments:

 

1. The US had issues with the .50 even in WWII and bungled a .60 development program that would have yielded something like the MG151/15 so even within the "Heavy Machine Gun" philosophy, there was recognition that the .50 was out of steam by 1945.

 

The US made several abortive attempts to acquire or develop better aircraft guns before and during WW2 but there was never much urgency behind it as the .50 proved adequate.

 

2. It's purely speculative, but I believe the US was the only air force that never faced a bombing offensive [the arguable exception being Japanese Betties, which may have been the most flammable combat aircraft in WWII]  and that this goes a long way towards explaining why they stuck with the .50

    USAAF night fighters, which were designed to engage bombers from the start, carried 20mm armament.

 

That is true, and doubtless accounts for the long life of the .50.However, it is worth noting that the two countries which did need to deal with heavy bomber attacks (Germany and Japan) found 20mm inadequate and were moving up to 30mm by the end of the war. The .50 was OK against fighters (provided it was carried in large numbers - which imposed a weight penalty); the 30mm was best against bombers; but a good 20mm was the best all-round compromise for WW2.

 

Tony Williams: Military gun and ammunition website and discussion forum

[Tony Williams]

Until the guy you're trying to shoot down with a missle has as good or better stealth technology than do you.  You might be wishing you had a cannon or two after watching your missles fly harmlessly by the guy who's now shooting his cannons at you.

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I didn't mean that modern fighter jets shouldn't have a cannon - IMO they certainly should have one - just that the calibre is no longer a major issue. Even so, the size, weight and cost differences between cannon, compared with a modern fighter, are so unimportant that you might as well fit a good one in the 25-30mm range.

 

Tony Williams: Military gun and ammunition website and discussion forum

[Guest bojan]

...I gathered that the Soviet cannon were kind of arcy.  Slow firing too.  At a leasurely 600rpm the M2, x 6, is giving 3600rpm...

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Both ShVAK and B-20 were fast firing- 800rpm.

Even 23mm VYa that was considered slow firing was 600rpm... And shell had 900m/s speed... Their 12.7mm were also fast - ~1000rpm...

Here is a table:

http://www.aviation.ru/gun/

Edited August 15, 2005 by bojan

[FormerBlue]

Both ShVAK and B-20 were fast firing- 800rpm.

Even 23mm VYa that was considered slow firing was 600rpm... And shell had 900m/s speed... Their 12.7mm were also fast - ~1000rpm...

Here is a table:

http://www.aviation.ru/gun/

207407[/snapback]

Early Mig-15 had 2 NS-23s and 1 NL-37 right? The NR-23 replaced the NS-23.

N-37, 690m/s, 400rpm

NS-23, 690m/s, 550rpm

NR-23, 690m/s, 800rpm. (Notes say USAF tests of a captured NR-23 showed actual max at 650rpm.)

 

None of these have any speed to write home about. Browning M3 is about 1200rpm? 866m/s?

[FormerBlue]

I don't "think" in metric so that will compound my mental twists. Let's check this.

 

F-86A top speed was 1072kmph. Let's slow it down to 800 to avoid top speed fight.

 

800kmph is 800,000 meters per hour right? 13,333 meters per minute. 222 meters per second.

 

F-86 is about 11 meters long. So it's going 20 plane lengths every second if it is flying sideways in front of you. If you have a cannon that the rounds travel 690 m/s, it takes more than a second for that to travel 1km. Of course we'd need to add the speed of the Mig-15 (let's say 800 also) for 1500 meters per second. If you are .5km back, your rounds will get there in 1/3 of a second right? The F-86 will travel 7 plane lengths in the time it takes for the rounds to get there. Did I screw something up? Top of the head math.

 

Let's give all 3 Mig cannon 800rpm. That would be 2400 rpm total. 40 rounds per second.

F-86 has 6 M3s. Let's call them 1000rpm each. That's 6000rpm. 100 rounds per second.

 

Even giving generous rates to the Mig-15s cannon, and slow rates to the F-86s, the F-86 is putting over twice the rounds out. The cannon rounds hit harder. Much harder. But the odds of a hit are less. The .50s get there faster. Less leading.

 

6000rpm with a mv of 1000m/s would be better than either I guess. But that would be the M61.

[Lev]

Let's give all 3 Mig cannon 800rpm.  That would be 2400 rpm total.  40 rounds per second. 

F-86 has 6 M3s.  Let's call them 1000rpm each.  That's 6000rpm.  100 rounds per second.

 

Even giving generous rates to the Mig-15s cannon, and slow rates to the F-86s, the F-86 is putting over twice the rounds out.  The cannon rounds hit harder.  Much harder.  But the odds of a hit are less.  The .50s get there faster.  Less leading.

 

But in your example you are essentialy simplifying to the point that being hit twice by any round is worse than being hit once by any round, regardless of the effectiveness of the rounds.

In reality the 23mm round is four times heavier than the .50, so even disregarding explosive effect the amount of lead the MiG puts on target in your example is well over twice that of the Sabre*. So even if it is twice as hard to hit anything with it, it would still be a better choice

 

 

* Using realistic values for rof for both sabre and MiG I get 5.5kg/s of lead put out by the Sabre, against 9 and 15kg for the MiG-15 and 15bis respectively.

Edited August 16, 2005 by Lev

[FormerBlue]

But in your example you are essentialy simplifying to the point that being hit twice by any round is worse than being hit once by any round, regardless of the effectiveness of the rounds.

In reality the 23mm round is four times heavier than the .50, so even disregarding explosive effect the amount of lead the MiG puts on target in your example is well over twice that of the Sabre*. So even if it is twice as hard to hit anything with it, it would still be a better choice

* Using realistic values for rof for both sabre and MiG I get 5.5kg/s of lead put out by the Sabre, against 9 and 15kg for the MiG-15 and 15bis respectively.

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No, what I was trying to show is the difficulty of gunnery in jet vs jet air to air. We didn't take into account the "droop" in the heavier rounds. I also went with a "perfect" side to side. The reality is the jets are never flying such perfect courses. They twist and turn like mad.

 

I'd check you weight figures but I just don't have the interest in digging up the figures.

[Paul Lakowski]

12.7mm API does about 860m/s at muzzle and by 400m its dropped to about 690m/s or 170m/s drop.

 

20mm WW-II American M-75 20mm AP does 770m/s but by 400m/s its doing 650m/s. or a 120m/s drop. I think 30mm Vdrop is less than 100m/s?

 

So effective range of MG falls off much faster than heavier cannons. Also while WW-II fighters did routienly survive MG strikes it took only one 30mm HEI shot to cut the average fighter in two.

 

Most post war countries concluded [correctly] that cannons were the way to go and didn't look back from their. Its no contest when you factor in heavier targets...you NEED cannons.

 

BTW I don't think any phantom drivers ever felt secure when they removed his cannons!

[FormerBlue]

Most post war countries concluded [correctly] that cannons were the way to go and didn't look back from their. Its no contest when you factor in heavier targets...you NEED cannons.

 

BTW I don't think any phantom drivers ever felt secure when they removed his cannons!

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I don't think I'm disputing that the cannons are the way to go. But that is assuming that the firing rate is higher.

 

Took a lot of effort to put that cannon back in the F-4. I've noticed that the F-22 and F-35 are still due to get a cannon. At the very least it retains some nominal value in keeping heads down when on a bombing run. A-1Es used to pepper the ground when they were going in.

 

Always thing outside of the box they say. Slow versus high rate of fire. Slow doesn't put a lot of chunks in the sky. High does. If I was going to go duck hunting tomorrow, would I be better served grabbing my Garand or my 11-87?

 

I do question the 30mm is fatal thing. The FW-190s had the 30mm. While it was probably very effective I'd wager that more than one P-47 returned after being hit with it. I guess it would depend on where the hit was.

 

I do recall reading an article where they examined a German 30mm postwar. I don't recall if it was the MK108 though. They were less impressed with the cannon than they were with the round it fired. Thin walls and lots of bang powder or somesuch.

 

Found it. It was the MK108. Victor Bilek did the study.

[EchoFiveMike]

The main purpose of modern aircraft guns is ground attack, hence HE throwing cannon.

 

Anything else is being completely impractical.

 

BTW,I've read that a large reason there were so many gun kills in VN is due to the stupid ROE's they worked under, in most cases requiring visual confirmation of the target.

 

Based on my experience, this seems extremely plausible. S/F....Ken M

[Ivanhoe]

BTW,I've read that a large reason there were so many gun kills in VN is due to the stupid ROE's they worked under, in most cases requiring visual confirmation of the target.

 

Missiles at that time weren't that effective in ACM. The Sidewinder was good, but we kept trying to make the Sparrow work. ROE did have a big impact, took away a lot of the easy shots at unsuspecting victims. Probably also took away quite a few shots at retreating fighters that were bingo fuel and thus vulnerable.

[FormerBlue]

The main purpose of modern aircraft guns is ground attack, hence HE throwing cannon. 

 

Anything else is being completely impractical.

 

BTW,I've read that a large reason there were so many gun kills in VN is due to the stupid ROE's they worked under, in most cases requiring visual confirmation of the target.

 

Based on my experience, this seems extremely plausible.  S/F....Ken M

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I'd tend to disagree with the VN thing.

 

F-4s in VN had two missiles: Sparrow and Sidewinder.

 

Max range on the Sidewinder was about 9 miles (D model). VN era sidewinders were not "all aspect" by any means and could break lock too easily. The L model was the first real "all aspect" model. Introduction on the L was 1978. P was better yet.

 

Sparrow had better range but had two disadvantages: active radar "painting" had to be maintained and it's manouverabilty was on par with a Peterbilt with a load of bricks. Kill probability on the Sparrow was less than 10% in VN. As I've mentioned before, they were pretty much used as attention getters.

 

I am aware that Sparrows were "semi-active." 1960s electronics were just not much to write home about. Solid state electronics were added to the Sparrow in 1976 which was much too late for VN of course.

 

I'd tend to separate missiles as being "moderately useful" against fighters until the late '70s. After that they are completely useful.

 

So I'd agree that today it's the case that the missiles are going to do what's needed. Amraams and the latest versions of Sidewinders should be able to manouver well enough to tag a fighter in most, if not all, cases.

[Paul Lakowski]

As I recall studies on the effectiveness of german guns vs B-17 showed that an average of 150 HMG hits were required to bring down a B-17 while only about 2 dozen 20mm shells were require.The same studies concluded that 3-4 30mm HEI hits were all that was required to bring down a B-17.

 

The only way a HMG is going to ever be as effective as a 30mm canon is if it achieves 40-50 times the hit probablity, which is extremly doubtful.

[FormerBlue]

As I recall studies on the effectiveness of german guns vs B-17 showed that an average of 150 HMG hits were required to bring down a B-17 while only about 2 dozen 20mm shells were require.The same studies concluded that 3-4 30mm HEI hits were all that was required to bring down a B-17.

 

The only way a HMG is going to ever be as effective as a 30mm canon is if it achieves 40-50 times the hit probablity, which is extremly doubtful.

207727[/snapback]

We've moved from F86 and Mig-15s to lumbering B-17s. Whereas the jets travel X airframe lengths (see above) every second, the B-17 is still kind of sitting there.

[FormerBlue]

As I recall studies on the effectiveness of german guns vs B-17 showed that an average of 150 HMG hits were required to bring down a B-17 while only about 2 dozen 20mm shells were require.The same studies concluded that 3-4 30mm HEI hits were all that was required to bring down a B-17.

 

The only way a HMG is going to ever be as effective as a 30mm canon is if it achieves 40-50 times the hit probablity, which is extremly doubtful.

207727[/snapback]

On second thought I'm curious on how such a study could be done.

 

First case. The Germans do it. What do they do? Count holes in crashed ones? What if the bombs blew? Crashed into the sea?

 

Second case. US does it. Same problem. Do the Germans radio their data over?

 

Third case. US does it with worn out airframes. How many? Do the B-17s get crews? I'd tend to think a .50 shooting back may affect shot placement.

 

I'm unclear how that data could be generated. Give me a B-17 flying straight and level, no guns, an I'm pretty sure I could consistently bring them down with a couple of rounds into the cockpit. No chin gunners allowed.

 

As I understand it Richard Bong brought down a Japanese fighter with IIRC 3 rounds. One of which went through the pilot's head. They recovered the plane so they were able to confirm the kill. Outside of this type of study I just don't see how the data was generated. The US would only have access to the airplanes that made it back. The Germans wouldn't have access to them.

 

How many .50s does it take to bring down a Mig? Same problem. How do you generate accurate data? Color me skeptical.

[Tony Williams]

On second thought I'm curious on how such a study could be done....How many .50s does it take to bring down a Mig?  Same problem.  How do you generate accurate data?  Color me skeptical.

207736[/snapback]

 

I think it was a matter of accumulating data which, while imprecise for any one event, gradually built up a picture. From the German viewpoint, they had gun camera footage and round counters. So they knew (on average) how many shots they fired at each plane to bring it down, and identification of the flash of the hits on the film backed up by examination of the wreck (when not totally destroyed in the crash) would tell them roughly how many of those shots hit.

 

Of course, in any individual instance the first shot fired might bring down the plane, or they could empty the magazines into it and it would still get back. Overall, however, the Lufwaffe worked out that it took three or four 30mm hits to bring down a heavy bomber, and 20+ 20mm hits. Since the hit probability was only 2-5% they worked out that a fighter armed only with 20mm could use up all its ammo on a B-17 without shooting it down, whereas a kill with 30mm was far more certain.

 

In Korea, I have read in US sources that over 1,000 rounds of .50 had to be fired by F-86s for each MiG-15 brought down. If the hit probability remained at 2-5% that meant that 20-50 hits were needed. In contrast, probably only about three 23mm hits - and only one 37mm - would normally have been required to bring down an F-86. Of course, the lower velocity and the different trajectories of the 23mm and 37mm cannon would have made hitting more difficult; the MiG-15s armament was primarily designed for use against bombers (they would have done better to replace the 37mm with another pair of 23mm). The four 20mm cannon used by the USN and Australian jets probably remained the best compromise in that war, but their planes weren't competitive.

 

In assessing the relative effectiveness of MG and cannon, the extra weight of the shells is of course only half the story - the other half rests with the blast effect of the HE and the fire risk from any incendiary material, which greatly multiplies the effectiveness of cannon hits. To give you a simple example, the best .50 ammo used at the end of WW2 (and still in use in Korea) was the M8 API, which had a steel core and 0.9g of incendiary material in the tip. The RAF's 20mm SAPI round had equal penetration, punched a significantly bigger hole (it was three times the weight as well as wider) and carried over ten times as much incendiary material.

 

Basically, a .50 has to hit something vital to score a kill; a cannon can inflict major damage with any hit.

 

Tony Williams: Military gun and ammunition website and discussion forum

[swerve]

BTW,I've read that a large reason there were so many gun kills in VN is due to the stupid ROE's they worked under, in most cases requiring visual confirmation of the target.

 

Based on my experience, this seems extremely plausible.  S/F....Ken M

 

Wasn't that a reaction to the risk of fratricide? When such a large proportion of the planes in the air are your own, you have to worry about the "Enemy sends up a plane to induce you to fire missiles at it, expecting you'll shoot down some of your own" scenario.

[Lev]

Tony beat me to it.

Edited August 16, 2005 by Lev

[Guest bojan]

...None of these have any speed to write home about. Browning M3 is about 1200rpm?  866m/s?

207467[/snapback]

 

950-1050rpm acording to Yugoslav F-84G mannual (it is just a translated US mannual)

[FormerBlue]

950-1050rpm acording to Yugoslav F-84G mannual (it is just a translated US mannual)

207789[/snapback]

I believe it can be controlled:

 

M3 .50 cal. Aircraft Gun. The Browning M3 aircraft gun was a .50 cal.  M2 machine gun that was modified for use as an aircraft gun that could be fired remotely by the pilot or gunner of a helicopter or light fixed-wing aircraft. The M3 .50 cal. aircraft gun was used in the XM14 gun pod. The M3 machine gun had a rate of fire of 1150-1250 spm. The M3 aircraft gun was classified Standard A.

http://tri.army.mil/LC/CS/csa/aawpns.htm#M3

 

That's an M3 mounted in a pod for helicopter use. It is an M3. Site is .mil.

[JOE BRENNAN]

I think it was a matter of accumulating data which, while imprecise for any one event, gradually built up a picture. 

 

In Korea, I have read in US sources that over 1,000 rounds of .50 had to be fired by F-86s for each MiG-15 brought down. If the hit probability remained at 2-5% that meant that 20-50 hits were needed. In contrast, probably only about three 23mm hits - and only one 37mm - would normally have been required to bring down an F-86. Of course, the lower velocity and the different trajectories of the 23mm and 37mm cannon would have made hitting more difficult; the MiG-15s armament was primarily designed for use against bombers (they would have done better to replace the 37mm with another pair of 23mm). The four 20mm cannon used by the USN and Australian jets probably remained the best compromise in that war, but their planes weren't competitive.

207756[/snapback]

I agree in the long run that picture did emerge, but also somewhat with Former Blue it's hard to nail it down without making assumptions that are hard to verify.

 

The closest one could come I think to combining real science and the intangibles of combat is something like the T-160 20mm GUNVAL project F-86's in 1953, your own planes of otherwise same type with different guns; however in that case marred by interface (gun gas ingestion) problems between the plane and gun it wasn't designed to carry. Stats showed better kills per sortie, but some didn't think it was a noticeable difference in effectiveness (but given subsequent history, most must have).

 

A USAF study of April 1951 (so that's without a huge amount of F-86-MiG experience) "Relative Effectiveness of Guns" considered the .M3 best of then existing weapons (v. .60, 20mm, 30mm), with tables illustrating. It projected its replacement with advanced 20mm (mentioned T-130) but didn't seem to show them quantitatively better per its statistical measures (again per later history, we might say wrong analysis, but again illustrates the difficulty).

 

MiG v. F-86 it's hard to draw any conclusion IMO about the effect of their armaments separate from all the other differences in the MiG and F-86 fighter forces. 1,000 .50 rounds per kill on average seems actually quite low, though I don't have an alternate figure. Whatever the rounds per kill, real kill let's say not claim, the number may have been higher for the MiG than the F-86, given the relative rate of fire ratio ballpark 3-4 times more rounds per F-86 per second of firing, but ~6 times as many kills by F-86's of MiG's as vice versa, and generally more MiG's than F-86's in the respective OOB's. The missing number there is whether F-86's got to positions from which they fired more often, but perhaps not since the MiG's *claimed* more F-86's than their own losses (but they scored a much lower, and low by historical standards, ratio of real kills as a % of claims). But again this just illustrates the problem of that kind of comparison, as opposed to one where at least some of the other variables are controlled.

 

Joe

Edited August 17, 2005 by JOE BRENNAN

[FormerBlue]

I think it was a matter of accumulating data which, while imprecise for any one event, gradually built up a picture. From the German viewpoint, they had gun camera footage and round counters. So they knew (on average) how many shots they fired at each plane to bring it down, and identification of the flash of the hits on the film backed up by examination of the wreck (when not totally destroyed in the crash) would tell them roughly how many of those shots hit.

So they were able to take the footage from an FW-190, a plane that was moving through a bomber box at over 400MPH, a plane that probably got less than a second worth of firing off before it passed the bomber, and identify individual hits by type?

That's just silly.

 

Bear with me as I fly all over here. Lot's of stuff raised.

 

BoB. Spits armed with .303 Brownings were able to knock down German fighters and bombers. That's a pretty small round.

 

.50, 20mm, 30mm are all ineffective in AAA role against B-17. The pilot I spoke with recently said even the 88mm wasn't really that effective.

 

Outside of the C-47s at Sicily, I can think of two cases where US AAA saw heavy use. In the Pacific they found that .50, 20mm, and 40mm weren't useful against the determined human guided missiles; most of which were single engine. Yet...

 

Armed with 6 .50s a number of US pilots were able to down 7 Japanese planes in a single flight. McCampbell? claimed 9 in one flight. I'd be curious what the single sortie record is for a German fighter. I don't know what it is.

 

The other real test of US AAA was the Ludendorff RR bridge. The "standard" defense of 90mm, 40mm, and .50s was used. Again, I don't know if it was rotate speed or RPM but the .50s were very effective:

The eight Stukas approached from the south along the river at 3,000 feet. MacGrain's radars easily acquired them at that altitude, and his 90mm fired away. Despite the AAA fire, the bombers took no evasive action. Some jettisoned their bombs before reaching the bridge, and one bomb did fall on the western approach to the bridge. That would be as close as the Luftwaffe would come to the bridge. Colonel MacGrain's battalion killed all eight aircraft, mostly with machine gun fire. Battery B of the 413th, the unit farthest to the south, was credited with four kills.

https://airdefense.bliss.army.mil/adamag/Hammer/Chapter6.htm

 

Interesting that the 40mm didn't get them. The .50s did.

 

But. I don't seem to recall the German Flak Vierling being very effective against P-47s either. Again, rate of fire? Rotate speed? Numbers? Aircraft speed?

 

Mixed calibers. The German fighters tended to have a cornucopia of calibers on the same aircraft. Is this because the heavies were somewhat immune to small calibers? Posters here seem to think that the 30mm was the answer. I disagree. I'll pick this up in a minute.

 

I believe it was the P-40 that resulted in the 6x.50s. The early P-40s had .30s and .50s. Trajectories were too different. I seem to recall reading a pilot recommendation to drop the .30s and just load more ammo for the .50s. I'd really really have to dig for that though.

 

Somebody listed weights for the F-86 and Mig-15 rounds. I think you might have used M2s. The numbers I see don't agree with yours.

 

20mm or 30mm? As stated the USAF preferred faster firing. I am unaware of reports from VN that the 20mm wasn't working. It seemed to do the job just fine. A 90mm would be even more destructive than a 30mm. What not use that? Bigger cannon are heavier and carry less rounds. They generally seemed to fire slower too. Mechanics of moving heavier rounds?

 

Let's go way out to left field. US Cruisers in WW2. 6" were useful. They had faster firing guns. 8" were sent off to hunt seals or some such. Rate of fire matters.

 

Mig-15 had two calibers. Maybe they felt the heavier cannon was needed for bombers. I'd not dispute that too much (see below). But I would note that the F-86 didn't intercept a lot of B-17s or B-29s. The 6X.50 worked well for them. Do the math on a Mig-15 and a F-86 only getting a 10th of second burst. Better yet, compute a full second burst with 10% hit probability. Either way the .50s are much more likely to hit.

 

M3 RPM. Is controllable as I understand it. 1200 was about max. 1200X6 is 7200rpm. Which is the "full rate" of the M61. Isn't that interesting? As Bojan noted, the F-84 was running them at about 1000rpm. Which is what the M61 is governed down to. Kind of interesting.

 

Navy experience was only the 5"/38 was really effective. That's quite a lot larger than 30mm. Maybe there is a middleground for hitting bombers. Well there is:

http://web.linix.ca/pedia/index.php/FFAR

F-89 used them.

 

Yes, a cannon round is more destructive than a solid machine gun round. That was why the original M1 was to get a coaxial BushMaster. But the M1 is shooting slow moving targets. The cannon is only more effective if it hits. .50X6 was very fast firing. As is the M61. But we don't have a time machine to put a M61 in the F86. We also don't have a ton of room. Remember the Germans strapping cannon in underwing gondolas? That didn't work well when fighters were about. 6x.50 is a pretty small installation all things considered. RPM is real high compared to 2 or 3 slow firing cannon. Compared to more modern cannon the cannon win. But that took time.

 

I entered the conversation based on Tony's? assertion that the F-86 was successful in spite of the .50s. Color me unconvinced.

 

Give me the F-86 with the six pack. And FFARs if I decide to turn on my bombers.

[Chris Werb]

Navy experience was only the 5"/38 was really effective.  That's quite a lot larger than 30mm. 

 

Wasn't that largely because it was the smallest (US Navy) calibre to take a VT fuse in WW-2? It might also be because, with the Kamikaze and later the AShM, you have to make the enemy plane depart controlled flight well before it hits - little or no chance of a second pass. Post war they went for 3"/70 as their optimum AA calibre/chambering because that was the smallest cal that could take a VT fuse and a worthwhile bursting charge. They never got the 3"/70 to work but they still had the 'stop-gap' 3"/50 weapon which proved much more successful.

[Tony Williams]

BoB.  Spits armed with .303 Brownings were able to knock down German fighters and bombers.  That's a pretty small round.

At the start of the BoB German planes carried little armour. This was rapidly amended during the Battle and the British fighters found it increasingly difficult to score kills, especially on the bombers (some got back despite being riddled with hundreds of .303-sized holes). The RAF was desperate to get the Hispano into action - they had recognised the inadequacy of the .303 long before WW2, which is why they ordered the Hispano in the first place - but it was just too late.

 

.50, 20mm, 30mm are all ineffective in AAA role against B-17.  The pilot I spoke with recently said even the 88mm wasn't really that effective.

When did B-17s fly in range of .50, 20mm and 30mm AAA? The 88mm used a time fuze, which meant that most of them exploded some distance from the plane, showering them with fragments but not usually bringing them down.

 

Outside of the C-47s at Sicily, I can think of two cases where US AAA saw heavy use.  In the Pacific they found that .50, 20mm, and 40mm weren't useful against the determined human guided missiles; most of which were single engine. 

As already pointed out, against kamikaze planes you need something powerful enough to effectively blow them out of the sky, from quite short range.

 

Armed with 6 .50s a number of US pilots were able to down 7 Japanese planes in a single flight.  McCampbell? claimed 9 in one flight.  I'd be curious what the single sortie record is for a German fighter.  I don't know what it is.

Hans-Joachim Marseilles is credited with shooting down 17 planes in one day, but I don't think that is particularly relevant. The kill ratios achieved by US pilots against the Japanese late in the war had a lot to do with the better trained pilots and the much tougher and more powerful US planes - and the fact that most Japanese fighters were easy meat for a battery of .50s.

 

The other real test of US AAA was the Ludendorff RR bridge.  The "standard" defense of 90mm, 40mm, and .50s was used.  Again, I don't know if it was rotate speed or RPM but the .50s were very effective

I have seen a calculated figure (from a US source) of 50,000 .50 AA rounds fired for every plane shot down in WW2. This compares with about 500 40mm Bofors rounds.

 

But.  I don't seem to recall the German Flak Vierling being very effective against P-47s either.  Again, rate of fire?  Rotate speed?  Numbers?  Aircraft speed?

On the contrary, it was deadly and much feared, according to the memoirs of a USAAF P-47 fighter-bomber pilot I have.

 

But I don't really see where you're going with this; are you trying to argue that the .50 was a more effective AA gun than a 20mm? If so, you're trying to defy some basic laws of science. The USN reckoned that their 20mm Oerlikons were ten times as effective as their .50 Brownings in the AA role.

 

I believe it was the P-40 that resulted in the 6x.50s.  The early P-40s had .30s and .50s.  Trajectories were too different.  I seem to recall reading a pilot recommendation to drop the .30s and just load more ammo for the .50s.  I'd really really have to dig for that though.

That would be entirely sensible. The .30 was not an adequate air-fighting gun by the time the USA entered the war.

 

20mm or 30mm?  As stated the USAF preferred faster firing.  I am unaware of reports from VN that the 20mm wasn't working.  It seemed to do the job just fine. 

In VN the main opposition were MiG-21s and even MiG-17s - lightweight planes even by the standards of the time, so the 20mm was entirely adequate against them. An unloaded Su-27 weighs more than three times as much as a MiG-21...

 

You should also note that during the Vietnam period the USAF was sponsoring the development of a very powerful 25mm cannon (the GAU-7), firing shells twice the weight of the 20mm, which was intended to equip the F-15; so they evidently weren't that satisfied with the 20mm M61. Its advanced combustible-case design ran into serious problems so it was dropped and the M61 substituted. At around the same time the reliability of AAMs began to improve, so gun performance became less of an issue. If guns were still important in air combat, it's a no-brainer that the USAF would have had a much bigger and more powerful gun in service long before now (probably the 30mm CHAG, which combined GAU-8/A ammo with a slim and lightweight three-barrel design).

 

A 90mm would be even more destructive than a 30mm.  What not use that? 

I might just as well ask: the 5.56mm XM214 Microgun was small and light, fired at 10,000 rpm and had a higher muzzle velocity than the .50 - surely by your criteria it would make a much better aircraft gun?

 

The answer is the same in both cases: the optimum aircraft gun is one which achieves the best balance between conflicting characteristics. Ideally, it will be light, fast-firing, have a high velocity for a short flight time, and achieve a one-shot kill. You can't have all of those things so you have to compromise. All aircraft guns, like all other military weapons, have always been compromises. The question which matters is therefore: which compromises give you the best chance of shooting down your opponent before he does the same to you?

 

In WW2, after the initial skirmishes which soon showed the inadequacy of rifle-calibre MGs, it became evident that the range for effective air combat guns lay between the .50 (at the bottom end of the range) and the 30mm (at the top end). The 20mm cannon was agreed by everyone (including the USN) except the USAAF as offering a better compromise. That doesn't mean that the .50 was ineffective; it did the job the USAAF needed it to do. But the standard battery of six .50s weighed much the same as four 20mm Hispanos, which were twice as destructive.

 

Remember the Germans strapping cannon in underwing gondolas?  That didn't work well when fighters were about.  6x.50 is a pretty small installation all things considered.  RPM is real high compared to 2 or 3 slow firing cannon.  Compared to more modern cannon the cannon win.  But that took time.

 

Six .50s weighed in at 174 kg (just the guns; excluding installation and ammunition weights). The gun weight for a late-model Bf 109 (one 20mm MG 151, two 13mm MG 131) weighed in at just 76 kg. Even adding two more 20mm underwing for bomber-destroying added up to only 160 kg in total. The weight of the battery of .50s could not have been accepted by most German fighters, which were generally smaller, lighter and less powerful than the American ones (that applied even more so to Russian ones). So the Germans and Russians went for cannon as providing the most efficient armament solution.

 

Tony Williams: Military gun and ammunition website and discussion forum

 

(edited to tidy it up a bit)

Edited August 17, 2005 by Tony Williams

[Miner]

Armed with 6 .50s a number of US pilots were able to down 7 Japanese planes in a single flight.  McCampbell? claimed 9 in one flight.  I'd be curious what the single sortie record is for a German fighter.  I don't know what it is.

 

Apart from the Russian front, an experten in a RAF night bomber stream could score pretty well eg the first combat evaluation of the He219 by Streib, 5 Lancs in 30 min (a flap failure wrote it off on landing).