# German 75mm v Allied 75mm



## vinnye (Jun 2, 2013)

Why did the German 75mm guns have so much better performance than any Allied 75mm?
Was it down to barrell length - Pak 40 having 46 calibres = 3.46 metres compared to M3 having 40 calibres or 3 metres?
They both seem to have the same range in weight of shot - from 7 to 14 pounds.
What else made the difference - firing charge, rate of spin?


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## Shortround6 (Jun 2, 2013)

Firing charge makes the biggest difference. Rate if spin is almost impossible to measure the difference. 

The US and British 75mm tank guns used a straight case 350mm long. The Pak 40 used a straight ( or gently tapered ) case 714mm long. Amazing what you can do with twice the propellant 

The AFV guns (Mark IV tanks, Stugs, etc) used a bottle neck case 495mm long but fatter in diameter. 

Short German 75mm (L24 used in early MK IVs and Stugs) used a case 243mm long. 

Check this website for A LOT of information. 

BOOKS BY ANTHONY G WILLIAMS


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## davebender (Jun 2, 2013)

Firing charge and barrel length work together. You need longer barrel to take full advantage of more propellant. KwK42 cannon shells fired by Panther tank had even more propellant to take advantage of very long 7.5cm/70 barrel.

Ammo quality is important too. Germany made some of the best shells including APC, APCR, HE and HEAT.

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## tomo pauk (Jun 2, 2013)

We can note that USA, UK and USSR did have 76.2 mm/3 in cannons/ammo in use, too (soviets and UK have had 2 of 76.2mm, notably different both in capability and numbers produced). The mere 1.2mm does not tell the story - it was, as in case of the 2 more powerful German cannons, the bigger casing using more propellant. The UK and USSR 76.2mm AAA ammo never arrived at AFVs (Soviets tested the gun for the AAA ammo, though), the lower power Soviet 76.2mm ammo (equivalent in power with French/US/UK 75mm) was used for ZiS-3 cannon and in T-34-76 and KV-1 mostly.
The most powerful Allied 3in class gun was the famous 17pdr, and we can also note the 75 and 77mm HV guns, equivalents (in power) with German 75mm L43/46/48.
US 3in was an 'legacy' gun, later the US built 76mm gun (for AFVs and as AT towed gun), both capable using same ammo as the 3in AAA? Again, equivalents in power with German 75mm L43/46/48.

The main and major advantage of the German 75mm stuff was it's timely arrival at war theaters.


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## Shortround6 (Jun 2, 2013)

tomo pauk said:


> US 3in was an 'legacy' gun, later the US built 76mm gun (for AFVs and as AT towed gun), both capable using same ammo as the 3in AAA? Again, equivalents in power with German 75mm L43/46/48.



The US 76mm used the same projectiles as the 3in gun but used a shorter, smaller case operating at a higher pressure to get the same ballistics.


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## nincomp (Jun 2, 2013)

To narrow down the the search on Anthony Williams website (link from Shortround) here is a page that shows the WWII German tank/antitank shells next to the Allied ones. My first response was "Wow, the allies had teeny weenie shells when compared to the German ones."
Scroll down to the picture of "German British WW2 Tank Gun Ammunition" in the following link. You will see that the British 17 pounder (76x583R) is the only Allied shell even close to the larger Axis rounds. Note the size of the 75mm round to the left of the 17 pounder. That was what most Sherman tanks used.
tankammo2

Most Americans do not know that the British upgraded many Sherman tanks with the 17 pounder in order to take on the Panthers and Tigers. They encouraged the US to do the same. Look up "Sherman Firefly." The Americans disagreed and refused to follow the British example. 

After landing in France, the Americans changed their minds and desperately wanted the Fireflys, but there were not enough to go around. To make matters worse, it was a very nasty surprise when the Americans discovered that the new, more powerful 76mm guns fitted to some of their Shermans were not nearly powerful enough to battle the larger German tanks on equal footing. The American commanders had previously been assured otherwise.


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## tomo pauk (Jun 3, 2013)

Shortround6 said:


> The US 76mm used the same projectiles as the 3in gun but used a shorter, smaller case operating at a higher pressure to get the same ballistics.



Thanks


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## davebender (Jun 3, 2013)

An expensive upgrade as it involved much cutting and welding of metal by hand. I wouldn't be surprised if Firefly Sherman total cost (original tank price plus modifications) was as much as a German Tiger tank.

To make 17 pounder cost effective the Chrysler tank plant would need to design turret and hull for that weapon and mass produce them that way. IMO that's a fine idea but Chrysler needs to begin design work for Sherman / 17 pounder variant during 1942 so they will be rolling off assembly line by end of 1943.


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## tomo pauk (Jun 3, 2013)

davebender said:


> An expensive upgrade as it involved much cutting and welding of metal by hand. I wouldn't be surprised if Firefly Sherman total cost (original tank price plus modifications) was as much as a German Tiger tank.



That's a bit too much, Sherman Firefly ending up as expensive as Tiger? Why we should consider cutting and welding as an hugely expensive exercise to get the Firefly up running?


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## davebender (Jun 3, 2013)

I have yet to see a price or man hour requirements for Firefly conversion. Have you?


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## Shortround6 (Jun 3, 2013)

And yet you estimate it to be equal to one of the most expensive tanks of WW II based on what?


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## fastmongrel (Jun 4, 2013)

The major turret mods were fitting a hatch for the loader and welding a box on the back for the radio. Dont know how thick the roof plate was on a sherman (say half an inch for argument) but the main difficulty is not cutting the metal which a good man with a gas axe could do in an hour or so but making sure the turret doesnt warp and throw the turret race out of alignment. The major mods for the 17 pounder were iirc a new mantlet, new recoil and run out cylinders and new ammo boxes. I believe turrets were modified and then fitted to new hulls which had the original turret removed co-drivers position removed and new ammo boxes fitted, these spare turrets then went through the modification shop and ended up on another tank.


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## nincomp (Jun 4, 2013)

davebender said:


> To make 17 pounder cost effective the Chrysler tank plant would need to design turret and hull for that weapon and mass produce them that way. IMO that's a fine idea but Chrysler needs to begin design work for Sherman / 17 pounder variant during 1942 so they will be rolling off assembly line by end of 1943.


 
No argument from me. From what I have read about the issue, General McNair, and probably others, kept such changes from happening. Gen. McNair believed that a tank's job was to support the infantry and the job of destroying enemy tanks fell to towed anti-tank guns and tank destroyers. Even after Tiger 1 tanks had appeared on the battlefield, he tried to cancel the M26 Pershing tank program, since in his mind, heavy tanks were pointless. 

One of the many problems with this doctrine was that advancing Allied tanks would come under fire from German tank and anti-tank weapons long before towed guns or even the tank destroyers could be moved up to the battlefield. Even when the Allied weapons were in place, the guns from Panther and Tiger Tanks as well as German tank-destroyers and towed 88mm cannons could shell the Allied weapons while staying out of range of those weapons.

It is somewhat ironic that General McNair was killed (by allied bombers) before the massacre of large numbers of allied tanks in Europe conclusively showed that his tactics were flawed. My (Canadian) father-in-law was watching at Caen when the British and Canadian tanks crossed the river and were largely wiped out. These forces did have some Fireflys, but they were too few to knock out their largely concealed opponents. Unfortunately, the Fireflys were easily distinguished by their long barrels with muzzle breaks and were targeted first by the German weapons. The tank commanders would have given almost anything to have had a Pershing tank at that time. My Father-in-law has often spoken about seeing one allied tank after another being destroyed.

There was no way in hell that he would ever volunteer to get into a Sherman Tank. Even on those occasions when he came under fire, he felt that his chances were better in a jeep.

Although this is straying from this thread, while I was doing an errand with my father-in-law this morning, he mentioned how fond he was of the Tiffys when they came in and attacked ground targets. In addition, he actually did see one Me262 in the air and wondered what in the hell it was.

If anyone wants to get some information from a former Canadian Colonel who worked for Montgomery, you had better ask soon. He is 95 and his short-term memory is getting worse. All of his "war buddies" are already gone.


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## davebender (Jun 4, 2013)

If that were true most Sherman tanks would have 105mm main gun. About 3 times as much HE as 75mm shell. Or perhaps 90mm/40 cannon which provides a nice increase in HE payload and adequate armor penetration.

I think it's more likely Gen. McNair and others like him were afraid to risk failure (and his General's pension). So they stuck with a tank/gun combination which was adequate and already in production.


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## Shortround6 (Jun 4, 2013)

At one point in the continual flip-flops that the tank production planners engaged in, 3/4 of all Shermans were to be armed with the 105 "howitzer" and 1/4 with the 76mm gun. Then they realized the Shermans might actually have to fight German tanks. 

There was NO 90mm/40 cannon available. And to design and build one would have been stupid even by US tank Ordnance standards. They had a perfectly good 90mm/L53 already available.


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## vinnye (Jun 5, 2013)

So the question now is - did the US ever put the 90mm L53 ,that they had available into the Sherman?


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## Shortround6 (Jun 5, 2013)

As the M-36 tank destroyer.

One model used the hull of the M-10. another model used the Hull of a regular Sherman.







Please note that this vehicle seems to have been upgraded with the gun from either the M-46 or M-47.


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## davebender (Jun 6, 2013)

Kanonenjagdpanzer - Wikipedia, the free encyclopedia
Main armament
1 x Rheinmetall BK 90/L40 90mm anti-tank gun 

According to Wikipedia this cannon was from U.S. M47 tank. Did the German Army shorten it to make it fit the Kanonenjagdpanzer?


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## Shortround6 (Jun 6, 2013)

I would be very careful about that. 

The gun certainly used US ammo but using old barrels seems a little much. Re-manufactured perhaps? 

The US guns were good for 700 EFC rounds (Effective Full Charge) so depending on training might have had a fair amount of wear. Not sure if a different recoil system was used. 

Rheinmetall also developed new ammo for the gun. Two different HEAT rounds and a HESH round. Apparently kinetic energy rounds were not used (or quickly replaced) in the Kanonenjagdpanzer as the primary AT rounds meaning a shorter barrel could be used. The HEAT projectiles being 5.74kg and the HESH projectile 7.45kg. The WW II 90mm AP projectile weighed 10,9kg.


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## kettbo (Jun 16, 2013)

davebender said:


> If that were true most Sherman tanks would have 105mm main gun. About 3 times as much HE as 75mm shell. Or perhaps 90mm/40 cannon which provides a nice increase in HE payload and adequate armor penetration.
> 
> I think it's more likely Gen. McNair and others like him were afraid to risk failure (and his General's pension). So they stuck with a tank/gun combination which was adequate and already in production.



The 75 worked fine in the M-3 Grant, so it was kept in the follow-on M-4. Just fine for bunker busting, MG position neutralization, and the like. US Doctrine was tanks were for iInfantry Support and break through. Those pulling the production strings needed quantity/ease of manufacture, reliability, size and weight to fit rail and ships...yes, must cross the Atlantic on a freighter. OH, they need to be able to be lifted by common cranes. Germans blew the permanent bridges, must be able to cross temporary or second rate bridges. A lot more to this than meets the eye initially.

The US 76.2 did not do well shooting HE. Shell was less effective. The AP rounds weren't all that great until HVAP vs Panthers and Tigers, AUG 44, but in short supply, most going to AT units. But the regular AP round performance was on par with the German 75mm rounds, Pzgr 39. The Pzgr 40 was not common, wish I had more details on the availability (or lack thereof)

Lots of Shermans, more Shermans in an Infantry Division than most Panzer Divisions had tanks

The M4(105) became available Summer of 44. Platoon of six for Fire Support for the Armored Bn. Not horribly effective vs tanks, looping trajectory. The 105 HEAT round, at closer range where hits are more likely, could do some damage. Ammo capacity would be a problem for general fitment. Then the logistics of planning for use of the rounds, manufacture, etc. Damn Bean Counters!


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## Civettone (Jun 17, 2013)

Shortround6 said:


> I would be very careful about that.
> 
> The gun certainly used US ammo but using old barrels seems a little much. Re-manufactured perhaps?
> 
> ...


That's right. The KaJaPa mainly fired HEAT and HESH, MV not mattering much. 
As such, it was only reasonable they replaced the gun by TOW missiles.

Kris


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## dobbie (Jun 17, 2013)

I think the biggest obstacle to US tank guns was that America really didnt get serious about building effective tank guns until 1940. The Germans and Soviets had a lot of experience in the Spanish Civil War and were continually upgrading weapons and chassis. The Sherman's first fight wasnt operated by the USA, but the British in North Africa, and at that time was considered a match for the MKIII and early MKIVs. The Sherman never was a good infantry support tank with respect to its armor-too thin, and it was expected that a true infantry support tank would need enough armor to survive the German anti tank defenses.

In truth, infantry support wasnt thought much of and our doctine was to have the infantry and artillery make a breakthrough so that armor would exploit it. Automotively, the Sherman was far superior to the MKV Panther but didnt have the power to penetrate the glacis. Our initial doctrine was based on the blitzcrieg tactics of the Germans, who changed their own thoughts after running into the Soviets. Our intial anti tank weapon was the 37MM based on the German model from the Spanish war. By the time we fielded our own 37, the Germans had moved onto the 57MM and then 75MM guns. The US was always behind in armor during the war. Good tactics, which included hitting the Panzer supply lines is what brought the German armor down.


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## Shortround6 (Jun 17, 2013)

Most people adapted other guns or ammunition to tanks. 
The US had the 37mm AT gun and tank gun using same ammo. 
the First 75mm used in the Grant used the ammo of the French 75mm field gun of 1897. Maybe loaded just a bit hotter. 
The long 75mm barreled guns used late Grants and production Shermans used the same ammo in a 9 caliber longer barrel for a modest increase in velocity.
The 3in gun in the M 10 tank destroyer was adopted from an old AA gun. 
The 76mm gun used in Shermans and M-18s used the same projectiles as the 3 in gun in a lighter barrel (same length for all purposes) in a smaller cartridge case operating at higher pressures ( The science of making gun barrels had advanced from 1918 to 1941/42).
The 90mm gun used in the M-36 TD and M-26 rank was adopted from an AA gun and the experimental 105mm and 120mm guns were also adaptations of AA guns. 

The US had leap frogged a number of other nations with the Sherman. 
From Wiki
" Detailed design characteristics for the M4 were submitted by the Ordnance Department on 31 August 1940, but development of a prototype had to be delayed while the final production designs of the M3 were finished and the M3 entered full-scale production. On 18 April 1941, the U.S. Armored Force Board chose the simplest of five designs. Known as the T6, the design was a modified M3 hull and chassis, carrying a newly designed turret mounting the Lee's 75 mm gun. This became the Sherman." 

The M3 was _always_ a stop gap.

wiki;
"The T6 prototype was completed 2 September 1941. Unlike later M4s, the hull was cast and had a side hatch, which was eliminated from production models. The T6 was standardized as the M4 and production began in October."

Please note that this was about *one year* before the tank saw action with the British. 

Unfortunately the US then did not keep up the pace and got side tracked with the the tank destroyer "doctrine".


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## dobbie (Jun 17, 2013)

Good points shortround....at the time of the M3, the only tank production line was at Rock Island and they were capable of making a few hundred tanks per year, and the American's werent even sure how big a turret ring needed to be in order to handle the 75MM gun. Thats why the sponson mount for the 75 and the 37 in the turret. The powder charge on the 75 MM gun is less than half of the German 75 or 17 Pounder British. I think the Brits were on the right track with their sabot round but the science was not well understood and it did not have the needed accuracy. HESH rounds were not all they could have been mostly because of the mechanical fuzes used at that time....the piezo electric fuze really helped the performance but that came after the war. 

I did read a bit on the 90MM turret from the M36 being dropped into a Sherman chassis, which gave them a more effective main gun, but even less armor on the turret and open topped to boot. 
I also see that some commanders balked at upgunning to the 76MM because its HE round was much less effective than the one used for the 75, and in a way one cant blame them. There was a lot less tank to tank battles on the western side than what the Soviets had to deal with. Terrain had a lot to do with that I suspect. Taking out an antitank position with solid shot is not nearly as effective as with HE and the Shermans dealt with a lot more of that than battling another tank. The big exception in the west was the British fight at Caan.


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## Mobius (Jun 19, 2013)

The charge on the German 75mm/L48 round was reduced at some point after it was in service because the casing ejection jammed. At some later point the charge of the German 75mm/L46 round was also reduced a bit. I'm not sure why this was done. Maybe to keep it's performace near that of the /L48?


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## MacArther (Jun 24, 2013)

One thing that explains the discrepancy between the German and Allied 75mm was at least on the part of the Americans the focus on the Tank Destroyer Doctrine. In this line of thinking, the Sherman would support the infantry, help with the breakthrough, and NOT engage enemy tanks! The enemy tanks were to be engaged by the M6, the M3/A1 gun motor carriages, and later the much improved M10, M18, and M36. Interestingly enough, when in their element and even out of it, the motorized anti-tank groups the Americans fielded did very well for themselves and their surrounding units! 

Look up*"The Tank Killers: A History of America's World War II Tank Destroyer Force,"* it has a good deal on the doctrinal ideas, as well as accounts for how the units fought at the front, and were eventually used as stand in tanks.


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## delcyros (Jul 12, 2013)

Armour in this period for tanks was homogenious rolled or cast armour. In some cases, units may employ some kind of improvisional face hardening applied as a thin, roughly 1.2" thick area on the plate´s face ("Einsatzhärtung") in order to obtain a higher hardening.

The preferred type of attack was a solid, uncapped AP-shot (no filler, just a tracer) in the US case and an APC (later APCBC) with small burster charge ("Zerleger") and base fuse element in the german case. Undenieable, the german projectile was more complex and labour intensive to mass produce.
Uncapped AP is quite good in defeating homogenious armour (requiring slightly less velocity than capped AP), provided it can remain in unbroken and unshattered condition. Beeing a solid AP-shot helps the M79 projectile here. The difference is not large but noticable, tehre is a correlation between the weight of the cap and teh striking velocity. A 15% cap requires 15% more velocity to penetrate a given plate at normal impact, while a 10% cap increases the velocity only by about 10% (US 3" and 6" AP/APC trials communicated by Dr. Allan Hershey in a paper called "The Cap effect and the Hood effect on penetration" or something like that)

However, with ever increasing impact velocities and/or impact obliquities, various forms of projectile damage may set in on uncapped projectiles. Nose shatter and breakage, deformation and compression (which a well designed projectile can limit) can be prevented by adding an armour-peircing cap, but base damage at high obliquity is more difficult to prevent. All these damages change the capabilities of the projectile to penetrate a given plate. Some changes actually may improve perforation (nose damage at high impact obliquity tends to prevent ricochet, for example, even though it would be a rare event), but any damage which is strong enough to change the perforation capabilities usually goes along with rendering the projectiles burster charge ineffective. This is a concern for the german 75mm AP as it was required to have at least some explosive effect within the target. 
Initially, the german 75mm AP would start to suffer breakage when striking 100mm homogenious armour at normal (1.33 cal/plate for this projectile). This compares unfavourably with the 3"M79 AP, in whiches case 5.14" rolled homogenious armour or 1.71 cal/plate (STS) were required to damage the projectile.
The germans then tried various forms of AP-caps, triggering dramatic improvements in their AP-performances. Higher striking velocities could be exploited now, which were previously unobtainable without risking full shatter of the projectile. I have seen a set of trials with 75mm APC penetrating a 200mm homogenious armour plate at 30 deg obliquity (2.67 cal/plate!) with neither nose nor body or base damage to any of these 75mm projectiles. One of which was stopped by the plate and another just penetrated with a third even stuck in the plate at striking velocities of in between 1030 and 1070 m/s.
At 30 deg obliquity, the 3"M79 would suffer breakage starting with 0.86cal/plate thickness (65mm for the 3"M79). The projectile could still completely penetrate -even thicker plates at this obliquity- but in completely shattered or badly broken up condition. It would also require more velocity than for an intact projectile (except at very high obliquities) and specially designed HVAP could exploit this to their benefit and attain better perforation figures. This explains, I hope, why the allies didn´t opted for higher velocity of their 75mm and 3" AP-shells with correspondingly smaller propellant charges. Higher striking velocities would have been possible and entirely feasable but AP-performance of uncapped AP wouldn´t have been much improved due to the soon developing shatter-gap.


Of course one has to keep in mind to compare apples with apples. The specification for hardness changed with the thickness of the armour plate. It´s possible to cross-calibrate the performance of the 75mm using a couple of data:

[1] Lilienthalbericht 166, p.110 for german penetration data -originally classified research paper detailing developments to 1943 in german AP ammunition -differentiating plate toughness 
[2] british trials with german 75mm as well as US and soviet 76mm AP/APCBC
[3] US trials with US 3" AP and german 75mm APCBC

according to these trials the british reports attributed the 75mm APCBC at 610m/s and normal impact with a penetration of 102mm. The corresponding figures from the Lilienthal file is only 90mm at this velocity. The latter beeing obtained against a plate of 147000 PSI UTS, suggesting that the british trials were executed at somehow softer armour plating (~130000 PSI UTS would yield the same penetrative result). The US trial gave apenetration of 190mm at 0 deg and 935m/s velocity -the corresponding figure of the Lilienthalreport was 186mm, obtained against a softer plate with 111000 PSI UTS.
Thicker plates had to be softer in order to avoid excessive brittelness under impact of the plate. The softer the plate, the better also the quality of the plate to perforation (less breakage) but the smaller the resistence to impact. However, once brittel breakage occured, the resistence of the plate dropped down by a considerable amount. The data of german and US trials suggest that the US trial plate was again softer than the german one, at around 108000 PSI.

Calibrated on a legend 115000 PSI plate (which is assumed to never fail by breakage- a theoretical vehicel for comparison purposes, as such plates wouldn´t be good at all thicknesses and outright poor in some), the corresponding adjusted figures for these guns would be:

at 610m/s:
75mm Pgr.39 --- 115mm penetration
3" M79 AP --- 102mm penetration
SU 76mm APC:-- 85mm penetration
-----
at 935m/s: 
75mm Pgr.39 --- 179mm penetration

The 3" M79 AP could be expected to about penetrate 160mm -theoeretically at 935m/s- but instead it will undergo full shatter striking any plate thicker than 130mm. US trials to investigate the problem showed that at about 635m/s impact velocity, shatter started to occur on this projectile with 5.14" STS armour, the shatter velocity beeing dependent on thickness and obliquity, too. Capped APCBC of this projectile, and HVAP introduced late 1944 were capable to match and exceed these data but only if a sufficiently high hardness of the cap and projectile nose was choosen. As a rule of thumb, it had to match or preferably exceed the hardness of the armour engaged.
If the nose was not hard enough -and shatter occurred- things can get complicated. At normal impact, the change from a pointed nose to a shattered is associated with a roughly 1/3 increase in required striking velocity to penetrate despite shatter (the fragments have enough velocity to smash completely through the plate) but this changes with increasing obliquity and gradually gets smaller.
Theoretically, it may happen that that a given projectile penetrates at 0 to 150 yards (penetration despite shatter by excess velocity), then fails to penetrate at 150 to 800 yards (shatter), then penetrates again at 800 to 1000 yard (penetration without shatter occuring) before failing completely.


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## Mobius (Jul 14, 2013)

delcyros said:


> Armour in this period for tanks was homogenious rolled or cast armour. In some cases, units may according to these trials the british reports attributed the 75mm APCBC at 610m/s and normal impact with a penetration of
> at 610m/s:
> 75mm Pgr.39 --- 115mm penetration
> 3" M79 AP --- 102mm penetration
> ...


Do you have the actual test results for these numbers or did you derive them from some sort of engineering formula? Real tests don't seem to agree. For example the US Aberdeen data Pak40 Pgr.39 ~635m/s @ 1500yds penetration=109mm.

At around 1575-1600m it gets to 610m/s where the penetration would be 104mm.

Then there's the US ballistic test of M79 in Handbook-of-Ballistic-and-Engineering-Data-for-Ammunition-Volume-2-USA-1950 stating that the Naval ballistic limit of 1911 f/s is 4". So 582 m/s is 102mm. At 610m/s the M79 would do about 107mm penetration (provided constant slope).

US tests were done vs. 230-250 BHN armor.


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## delcyros (Jul 26, 2013)

> Do you have the actual test results for these numbers or did you derive them from some sort of engineering formula? Real tests don't seem to agree. For example the US Aberdeen data Pak40 Pgr.39 ~635m/s @ 1500yds penetration=109mm.



As mentioned previously, the penetration data I referred to are ESP figures. Thus, it´s theoretical performance based upon a calibrated steel armour plate (homogenious) with 115,000 PSI tensile strength.* E*quivalent *S*teel *P*enetration. This way, it´s possible to compare the data from different trials using different plate properties.
Note that penetration is usually based upon interpolation of multiple shots under similar condition. You get a scatter of individual penetration events and try to lay a best fit curve through the cloud. I have the M79 "clouds" and now that a certain scatter of data realistically has to be reckoned with. The typical form to determine the grenz penetration (100% of the projectile through the plate, broken or not and completely depleting it´s energy) was:

850ms---840ms---830ms---820ms--
--+--+--+--+--+--()--+--()--(o)--(o)

where
+ is complete penetration
() is stuck in plate
(o) no penetration

-in this case the limit of perforation would be considered ~838m/s to 830m/s

The effect of tensile strength (correlated with BHN hardness as long as ductile under impact) is most significant for normal impact (0 deg in british, 90 deg in german definition) but reduces with obliquity. As an example, trials conducted 1942 with 2cm model shots (Ss and SK) on 50kg/mm^2, 100kg/mm^2 and 150kg/mm^2 plates respectively showed that at 90 deg impact tripling the tensile strength resulted in a quadruple of resistence compard to soft plates while at 60 deg obliquity the difference between 50kg/mm^2 and a 150Kg/mm^2 plate was just 6%-almost identical. This is correct and one of the reasons why relatively soft, aluminium armour plate has replaced steel armour plate in high obliquity applications, since. 

My penetration figures are entirely consistent with individual trial data. Note that ESP is more difficult to penetrate in great thicknesses but easier to penetrate in thin ones, caused by the fact that thinner plates from real trials can and have been heat treated more carefully and kept ductile despite higher tensile strength. Thicker plates would be more brittle and thus have to be kept softer. ESP is not changing it´s hardness or ductility properties with scaling up or down thicknesses, unlike real armour plate in real tests.

That beeing said, yes, my data is based upon primary sources for firing trials with known projectile-, plate performance and penetration definitions.
I can exactly determine the penetration of the 75mm Pgr.39 (APCBC with small "Zerleger" HE-filler) at 0 deg(vertical), 30deg, 45deg and 60deg obliquity. I can also exactly determine the plate quality in the individual penetration and I know precisely how these figures communicated in the then classified 1943 source were arrived with. What I cannot determine is the corresponding distance as I have only prooving ground data which do not reference the distance but the striking velocity, instead.
What is needed is a ballistic datafile for the various 75mm gun´s firing this projectile with the drop of velocity plotted against range.
Note that I consider these data much (!) more reliable than data posted in secondary sources, as they are more complete and extracted from a large number of projectile prooving ground (primary..) trials covering low, middle and high obliquities and basically all possible striking velocities in addition to discussions when projectile breakage sets in for specific conditions.



> US tests were done vs. 230-250 BHN armor.


Unfortunately, this conception has turned out as incomplete. While much testing was indeed done in this region, different BHN values were trialed, too (corresponding to 215BHN min and 265BHN max). I have almost all data for the M72 AP from Dr. Allan Hershey´s records at the USNPG and can identify the plate properties from these trials.


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## Mobius (Jul 26, 2013)

delcyros said:


> The effect of tensile strength (correlated with BHN hardness as long as ductile under impact) is most significant for normal impact (0 deg in british, 90 deg in german definition) but reduces with obliquity. As an example, trials conducted 1942 with 2cm model shots (Ss and SK) on 50kg/mm^2, 100kg/mm^2 and 150kg/mm^2 plates respectively showed that at 90 deg impact tripling the tensile strength resulted in a quadruple of resistence compard to soft plates while at 60 deg obliquity the difference between 50kg/mm^2 and a 150Kg/mm^2 plate was just 6%-almost identical.



That must be a different report on the same subject, BHN vs. Penetration, that I have:

Watertown Arsenal Laboratory
Report Number 710/607
Problem Number J-1.2
Principles of Armor Protection
Partial Report, no 1
14 April 1944

I wrote a program that calculates relative armor quality based on these tests.
But I am not confident if these small scale tests scale up to real world well.



delcyros said:


> What is needed is a ballistic datafile for the various 75mm gun´s firing this projectile with the drop of velocity plotted against range.


I have quite a bit. I use it to test my ballistics program.
For the German 75mm/L48:
RANGE..75L48
0m......750
100m....738
500m....691
800m....659
1000m...637
1500m...585
Weight..6.8

3-in,76mm M79 
0........2600(792)
500.....2330(710)
1000...2070(632)
1500...1840(561)
2000...1620(494)
2500...1425(434)

Note that such a study similar to yours has been done before. From the tanker's forum:


> British tests against homogeneous armor at 610 m/s impact velocity, which are documented in Miles Krogfus' AFV News article, resulted in:
> 102mm penetration for German 75mm APCBC
> 90mm penetration for U.S. 76mm M62 APCBC
> 75mm penetration for Russian 76mm APBC





delcyros said:


> I have almost all data for the M72 AP from Dr. Allan Hershey´s records at the USNPG and can identify the plate properties from these trials.


I only have a document on the M79 giving two points of NBL penetration. The velocity of 4' and 3' penetration. I would like a document on the M79 with more data points. Maybe we can do some document horse trading?


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## delcyros (Jul 26, 2013)

> That must be a different report on the same subject, BHN vs. Penetration, that I have:
> 
> Watertown Arsenal Laboratory
> Report Number 710/607
> ...



If You have that, You will perhaps be interested in some of the files I have, too. The relevant information in the respective context I extracted from DIE VORGÄNGE BEIM BESCHUß VON PANZERPLATTEN, Lilienthalgesellschaft für Luftfahrtforschung 166 (Berlin 1943), in an article written by W. Schilling, EINFLUß DER PLATTENFESTIGKEIT BEIM PANZERDURCHSCHLAG (p.62ff).



> For the German 75mm/L48:
> RANGE..75L48
> 0m......750
> 100m....738
> ...



Thanks. I will keep a copy but would like to know the source. The relevant perforations for homogenious armour these values and PGr.39 (6.8kg with "Zerleger" , cap and ballistic windscreen) are:

750m/s:
0 deg*: 130mm (85-90 kg/mm^2 tensile strength in trial plates)
30 deg: 103mm (100kg/mm^2 tensile strength in trial plates)
45 deg: 66mm (110-105kg/mm^2 tensile strength in trial plates)
60 deg: ~45mm (extrapolated. Closest penetration was at 850m/s on a 53mm thick, 115Kg/mm^2 trial plate)

691m/s:
0 deg*: 114mm (95-100 kg/mm^2 tensile strength in trial plates)
30 deg: 90mm (100-105kg/mm^2 tensile strength in trial plates)
45 deg: 59mm (110kg/mm^2 tensile strength in trial plates)

637m/s:
0 deg*: 98mm (100 kg/mm^2 tensile strength in trial plates)
30 deg: 80mm (105kg/mm^2 tensile strength in trial plates)
45 deg: 52mm (110kg/mm^2 tensile strength in trial plates)

585m/s:
0 deg*: 87mm (100-105 kg/mm^2 tensile strength in trial plates)
30 deg: 72mm (105-110kg/mm^2 tensile strength in trial plates)
45 deg: 47mm (115kg/mm^2 tensile strength in trial plates)

*using english definition: 0 deg = normal impact. Based upon penetration curves drawn from executed shooting trial, -not theoretical calculation. The plate tensile strength is mentioned. Definition was intact penetration for 0 to 45 deg impact and nose broken for 60 deg, the complete projectile has to pass the plate and deplete it´s energy ("grenz"). Primary source data:

J. Sitz, EINIGE PRAKTISCHE ERFAHRUNGEN IM PANZERPLATTENBESCHUSS BEI DER ENTWICKLUNG VON PANZERGRANATEN ÜBER 3,7cm BEIM HEER, in: DIE VORGÄNGE BEIM BESCHUß VON PANZERPLATTEN, Lilienthalgesellschaft für Luftfahrtforschung 166 (Berlin 1943), 109-113.

If You normalize these data, You may find it helpful to pay attention to the dynamic relationship between obliquity and tensile strength. 


I for my part, have never been surprised that no gun defeated the T-54A frontal slope in yugo tests. The front slope was close to 60 deg and no AT- or Tank gun in ww1 had the performance to penetrate a close to 100mm plate in this obliquity range, regardless of ammo type. Unless, perhaps You happen to hit repeatedly the same spot, group impacts close to each other or hit weak spots, which jointly occur. 

Hope, it helps.


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## Mobius (Jul 26, 2013)

I found the 75mm data on 10+ year old posts on the Battlefront Combat Mission site by Rexford (Lorrin Bird, author of WWII Ballistics:Armor and Gunnery). In his post about dispersion and firing tables I found that his 88mm/L71 data matches that of the German 88mm/L71 firing table (which I include it in the PAP.zip) so I am assuming his 75mm is good as well.
I don't know where the links are to the pdfs but I do have them so I uploaded them in zip form to my website. (I'm not going to keep the links up long as I don't want Google or other webcrawlers to link to them.)

Principles of Armor Penetration and the rather large Handbook of Ballistics ... etc which has a few pages on the M79 round.
http://www.panzer-war.com/Files/PAP.zip
http://www.panzer-war.com/Files/HBD.zip

I've tried to normalize my data too but I have to ground them in reality. So...
There's a poster at tank net and WOT named Bojan who posted 1950-1960ish Yugoslav tests where they tested the 76mm M79, 75mm Pak 40 and 76mm Zis-3 on the same targets. Now that is normalized!


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## Mobius (Jul 26, 2013)

Speaking of the yogo tests.

Let's look at it in a different way. Find the velocity that a shell is travelling at the range that it does penetrate.

Complicating matters we don't know what the muzzle velocity is of the tests.
The 75mm Pak 40 velocity was reduced at some point after entering service. This apparently confounded the US and USSR in testing of the captured weapon such that they at a point listed the muzzle velocity as 770m/s (probably an average of old and new rounds).

In the late war ZiS-3 the BR-350B appears to have an improved version also a BR-350B.
Since I don't know what the muzzle velocity is for some guns I include both for comparison.

Tests on target vehicles:

T-34 [email protected] 350BHN 90mm-rounded 444BHN
..........................glacis..........turret
75mm 750m/s.....1300m=605...1000m=637
or
75mm 790m/s.....1300m=639...1000m=672
76mm M79.........1100m=601.....900m=633

Sherman..... [email protected] 250BHN... 90-94 rounded 230BHN 
...............................glacis.........turret
75mm 750m/s........1100m=626......1000m=637
or
75mm 790m/s........1100m=661......1000m=672
76mm ZiS-3 662m/s..250m=638.......350m=629
or
76mm ZiS-3 680m/s..250m=656.......350m=646


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## delcyros (Jul 27, 2013)

What formula do You use to normalize BHN values?

p.s. drop me an email and I can send You some files.


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## Mobius (Jul 27, 2013)

I start out with something like this:
BHN adjustments 
My Baseline BHN=270 (1.0)
German=275 (1.0182)
British=263.5 (0.9866)
US=240(230-250) (0.941)


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## delcyros (Jul 29, 2013)

> I start out with something like this:
> BHN adjustments
> My Baseline BHN=270 (1.0)
> German=275 (1.0182)
> ...



Ok, I understand. However, I have some issues here.
[1]
BHN varies -among other things- with thickness of armour (at least in US, british and german sources) 
[2] why not use Z-or BCNF-normalisations instead to avoid assymetries?
[3] using 270BHN as a guideline, some of the russian turret armour would be roughly 60% more resistent (at normal impact) than those mentioned above but this isn´t supported by sources.


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## Mobius (Jul 29, 2013)

delcyros said:


> Ok, I understand. However, I have some issues here.
> [3] using 270BHN as a guideline, some of the russian turret armour would be roughly 60% more resistent (at normal impact) than those mentioned above but this isn´t supported by sources.


That's why I didn't include Russians or cast armor. Russian hardened RHA acts well vs. undermatched projectiles. For overmatched not so much: 350 BHN acts like 260 BHN. From yugo tests cast hardened rounded 444 BHN T-34 turret acts like 260 BHN. But then from the same test 230 BHN cast rounded M4A3 turret also acts like 260 BHN.


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## delcyros (Jul 29, 2013)

As far as vertical plate is concerned, the drop in quality of russian plates can be explained by impact load failure. This is not exactly the same as impact britellness but it's not ductile anymore. I have some data that indicate that if the plate is not ductile and fails to shatter the projectile's nose, it looses roughly 1/3 of it's ballistic resistence because the plate is much less tough and fails rapidly and completely from surface to back.
Russian armour would fare very well against uncapped and soft capped AP (which it really did) in vertical impact but APC is a different thread, exposing it's lower impact load tensile strength. Small shells may not reach the critical impact load at all.


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## Mobius (Jul 29, 2013)

So, then that would be the type of armor the Russians tested their shells on.


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## delcyros (Jul 29, 2013)

Possible, I have very limited data on soviet projectiles and armour plate. But remember, that´s for normal impact. Increasing the obliquity not only enhances protection but also reduces the difference of all qualities. This is correct because at very high obliquity, even water causes regularely a projectile to ricochet off. At high obliquity, a soft but ductile plate has benefits over a hard one even if it´s much softer because
[A] difference in hardness / toughness are less severe than at normal impact
* it tends to affect the trajectory of the projectile less during penetration (normalization of impact angle). This effect usually makes intact penetration more difficult for hard plates (body breakage is common) but requires less velocity to penetrate than a similar soft plate
[C] it can cause EASIER penetration for soft capped and uncapped AP due to nose shatter or body breakage which cause the changed projectile nose (blunter now than originally) to bite better in the plate*


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## MacArther (Jul 30, 2013)

US Penetration tables for the M2 and M3 Tank Guns
United States' 75 mm Gun Penetration Tables - World War II Vehicles, Tanks, and Airplanes

Comprehensive listing of most German 75mm guns performance
Germany's 75 mm Penetration Tables - World War II Vehicles, Tanks, and Airplanes


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## delcyros (Jul 30, 2013)

Thanks. But You will notice, the list is based upon secondary sources. The following excerpts are from primary source documents detailing the development of armour-piercing capped shell in Germany. The original is entailed in the Lilienthalreport 166 files I quoted above.

[A] State of AP-performance through 1940/41:

Generally, german AP was uncapped APHE, except for 8.8cm and 7.5cm which were APCBC-HE but both with a relatively large explosive filler, which had potential to cause very severe damage but also compromised penetration capability. 





The appearence of the Char B1 bis and Matilda tanks caused new and higher requirements for armour penetration. the easiest way to improve performance was to increase striking velocity. However, all german AP of this period would shatter at high velocities and any increase in striking velocity would not result in a similar gain in penetration performance. There were two solutions:

[A] improve the properties of the projectile. This can be done in two ways, first one could get rid of the filler or at least make it smaller or alternatively, introduce sheath hardening as employed by Krupp for the KM naval L.4.4 type APCBC projectiles. Sheath hardened projectiles have the highest hardness at the surface and go softer to the inner cavity of the projectile thus high hardness can be found on all surfaces like a cocnut enveloping a softer core. The decremental hardening is more useful for mass production (hardness is highest in the nose and gradually -in one level from side to side- goes softer towards the base), however and sheath hardening wasn´t employed outside the Navy and experimental prooving grounds.
* add an armour piercing cap with an as hard as possible surface hardness gradient. The initial APCBC had soft caps (soft caps don´t work outside very limited parameters of obliquities 0 to 15 deg) but replacing them with hard caps (440 to 560 BHN) resulted in prevention of nose shatter. high striking velocities thus could be exploited for the firt time. The solution is easier for mass production, too. The following graph shows the differences between old and new type 7.5cm APCBC, in mass production and service by 1943:





You will notice how the Pgr39 get´s more penetration by enjoying more velocity while the Pgr rot suffers breakage precluding any higher penetration due to soft cap failure. The Pgr39 is actually a pretty interesting projectile, beeing a composite one with part of the nose detached from the body and acting as an auxilary AP-cap und the thick AP-cap. The prooving ground committee was enthusiastic about the Pgr39 performances in combination with high velocity guns and some very ridiculous thicknesses were trialed to explore the limits of the new projectile. The following is a trial with a 200mm thick RHA armour plate carried out 1942. It was successfully penetrated at 1090m/s velocity by the Pgr.39 on 30 deg obliquity (= 30 deg inclined from the vertical and normal impact -german definition was 60 deg because they considered 90 deg as normal). This is quite interesting, one projectile at 1020m/s just made a bulge and was recovered in front of the plate (intact), the projectile striking at 1070m/s velocity stuck in the plate (penetration according to british and US Army definition and partial penetration according to US Naval Ballistic Limit definition) but the "grenz" definition required that the complete projectile (100%) had to be recovered behind the plate, that´s why the 1090m/s figure also found entry in the 
penetration tables.





It appears that the 75mm Pgr39 was the primary study object of the ballistic research dep. and various obliquities were trialed with this projectile covering right angles impact as well as 30 deg, 45 deg and 60 deg high obliquity impact studies. The corresponding results are reproduced below:





Note how difficult it appears to penetrate anything at really high obliquity (45 to 60 deg), and how exceptional the penetration capability at right angle´s impact was. Similar studies have been executed -albeit at a smaller scale- for other projectiles and most of the data have been standartised for 30 deg obliquity impacts, the following graph gives various 1943-period APC performances at 30 deg obliquity: 





Late war, much intention was paid to increase the obliquity performance of the projectiles. You can realize that the trend was generally to go for blunter headshapes and flat APcaps in order to improve the biting angle and prevent ricochet.
The 88mm Pgr.39/43 still had a very pointed headshape, 1.47crh (the US M79 AP had 1.67 crh), which allowed for optimum penetration at 15 to 45 deg obliquities. The 100mm APCBC was down to 1.35 crh and the 128mm APC which was issued later further down to 1.29 crh with a completely flat cap and no windscreen. The 75mm was reduced from 1.53crh at around 1940 in the 7.5cmK.gr. rot Pz.Gr. to only 1.1crh in the PGr.39 for 1943 and correspondingly had quite credible high obliquity performance for her period. The further reduction of the point was on schedule with plans for a new model P.Gr.45 88mm and 75mm APCBC with only 0.93 caliber radius headshape combine dwith a thick and flat AP-cap under a very pointed break away aluminium ballistic windscreen. 

hope it helps,
delc*


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## vinnye (Jul 31, 2013)

Does anyone have data on how the Russian 76mm compared to their German / American equivalents?
There is annecdotal evidence of the impact of the T34 being impervious to AT fire - unless it was the 88mm!
But, I do not recall much about its firepower?


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## Mobius (Jul 31, 2013)

vinnye said:


> Does anyone have data on how the Russian 76mm compared to their German / American equivalents?
> There is annecdotal evidence of the impact of the T34 being impervious to AT fire - unless it was the 88mm!


Here's a perspective:
http://www.tank-net.com/forums/index.php?showtopic=18562&hl=yugoslavian&st=0


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## Mobius (Aug 9, 2013)

I found this on high hardness armor.


> Trends in Soviet Metallurgical Developments
> Central Intelligence Agency
> Washington 25, D, C.
> 16 April 1953
> ...


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## delcyros (Jun 11, 2014)

Added new information -apologies for 88mm instead of 75mm data.

I have tried to register in tank.net but unfortunately, they generally don´t accept new memberships in the moment.
I am just writing here in order to offer some thoughts about the discussion of IS-2 obr.44 armour vs KWK43 88mm/71 using APCBC. Particularely with regard to the aspect of the upper front plate (glacis plate) versus penetration or its alleged immunity. It has been suggested by Bojan -citing the later Yugo trials on T.54 glacis plates whiches the 88mm APCBC couldn´t penetrate- that the upper front plate of the IS-2 mod. 44 (100/110mm @ 60 deg) was correspondingly also immune to penetration at any range from 88mm firing either APCBC or APCR.
In this context, direct evidence is hard to come by but the IS-3 penetration trials are significant for the question, as it details also include -among others- the penetration of 88mm vs IS2 for both, upper and lower front plate. Being a russian source, it has primary source character and should not be rejected easily as holding no reference to IS-2, people who compiled the report only notified the results but they indeed had access to all results, not just the few we know today. While the document deals primarely with IS3 in order to demonstrate the improvements attained by russian tank design in beating the high performance german 88mm KWK43 /PAK43, it also contains valuable data for the IS2, too and is more likely to make use of the latest APCBC ammo (Pgr 39/43) captured in Germany than earlier documents deteailing penetration of IS85 or T34.

I quote the relevant passage:


> Нос корпуса
> 
> Выбранная конструкция носовой части корпуса танка ИС-3 аначительно увеличивает снарядостой-кость этого узла по сравнению с носовой частью серийного корпуса ИС-2, за исключением передней наколонной част и крыши корпуса.
> Верхние лобовые листы корпуса ИС-3 полностъю зацицают экипаж от 88мм немецких бронебойных снарядов с дистанция 100 метров и более, при любых углах обстрела.
> *Верхний лобовой лист корпуса ИС-2/Уралмашзавода/ непробивается толъко дистанции 600 метров и далее.*



The bold lines demonstrate that the soviets did considered the glacis of the IS-2 to be proof from 88mm at distances of 600m and more -suggesting that inside this range it was very vulnerable.
A later page detailing the lower front plate says that the IS-3 was able to repell 88mm from larger distances than 300m while the same aspect on the IS-2 could be penetrated at 5100m (!).
This soviet era source points out that the frontal glacis plate of IS-2 can be penetrated by 88mmL71 APCBC inside within 600m while the lower plate can be penetrated in excess of 5000m, the huge difference entailed in both numbers (600m vs 5100m) is a valuable secondary information and in effect rules out the possibility that the IS obr.43 is referred to here in source instead of the IS-2 obr.44. The IS-2 obr. 43 had 30 deg sloped 120mm plate (from the vertical) for the „step“ on the glacis and a similarely 30 deg declined lower front plate of 100mm. Thus minimal differences in striking velocity are required to penetrate both plates at similar angle (~680m/s lower front plate vs 750m/s upper front plate for the 88mmL71 using Pgr.39 using official WaPrüf penetration curves for post 1943 APCBC on german RHA). Only the IS-2 obr. 44 had the required difference in upper and lower front plate (110/[email protected] 60 deg glacis vs 100/90mm @ 30 deg lower front plate) to explain the distance discrepiancy mentioned in the soviet prooving ground report.
This doesn´t explain why the T54 glacis wasn´t penetrated at all even from close range. It doesn´t need to. The T54 is a younger, more advanced metallurgical design. It benefitted from all late war research conducted and the data gathered in Germany and abroad which helped to produce the best plates for a specific purpose.


It is also necessary in this context, and I think overdue, to make clear - having compiled sufficient body of evidence- to suggest that plate hardness is not important at all under high obliquity impact. While against vertical plates and even moderately declined ones armour plates of high BHN levels significantly improve the ballistic resistence (sometimes, if the plate is able to shatter some of the older, or weaker capped and all uncapped projectiles by a very considerable margin - shatter yields in a ~1/3 raise in necessary striking velocity to perforate plate), they don´t do it at 60 deg. I have the results of systematic penetration trials conducted with different BHN level good RHA armour plate (even mild steel) at varying obliquities to proove this. Differences in ballistic resistence drop to being negliable against extremely sloped plate. (a gain in 30kg/mm^2 tensile strength equals only about 5% gain in resistence at 60 deg as opposed to 25% for a vertical plate)
More important than hardness is that the armour plate -be it cast or RHA- is entirely free of flaws, has a fine grain size and -orientation and contains no internal laminations and remains ductile under dynamic impact stress. Overly hard armour plates tend to be more brittle and flaw affected than ductile ones in comparison. The decision, f.e. to make the PzIII, PzIV and TIGER-I´s vertical armour plates very hard but the HETZER´s and TIGER-II very oblique sloped frontal plates comparably soft in fact represents a sensible and correct application of ballistic research carried out in Germany in the early 40´s (compare Lilienthal report 166). Soft but highly sloped armour improves toughness under impact and allows the plate to stretch making deflections and ricochet more likely. A harder front plate, as was practice in soviet union still at the end of ww2 would likely even have reduced the level of ballistic protection here, such as mentioned also in US Watertown reports for impact under high obliquity.
Flaws in armour plate may result in roughly 1/3 loss (25% to 40%) in effective thickness and explain why ,f.e. a 28mm s.PzB.41. was able to pierce the lower front plate of an IS-85 (with stepped hull and 100mm cast carmour) in one documented case 1944, a performance which is well beyond the scope of the certified penetration of [email protected] 30 deg and short range credited to this weapon. Also the failure of lower plate armour at distances of ~5km as cited by russian IS-3 document can be seen as a strong indication of the existence of such flaws in armourplate. Armour plate of the period was hardly ever systematically tested at very high obliquity (60 deg realm) before well after end of ww2. A flawfree, and soft armour plate (~205 to 220 BHN) would probably have eleminated the vulnerability of the glacis of the IS-2 mod.44 against 88mm KWK but as it is, the frontal aspect appears not to be impenetrable from medium and close range while the lower front plate, which makes for roughly 40% exposed frontal hull target area, is virtually penetrable by this gun using late model Pgr 39,1 at any realistic fighting range.

hope it helps,
delc


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## pbehn (Jun 11, 2014)

Some great info posted here, I must say that with all the development of aircraft, aircraft carriers and anti submarine warfare it is lamentable that the allies were so far behind in Tank development, seems the USA and UK/Canada and other allies were always way behind in fire power armour and HP.


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## pbehn (Jun 11, 2014)

duplicate


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## Mobius (Jun 11, 2014)

delcyros said:


> This doesn´t explain why the T54 glacis wasn´t penetrated at all even from close range. It doesn´t need to. The T54 is a younger, more advanced metallurgical design. It benefitted from all late war research conducted and the data gathered in Germany and abroad which helped to produce the best plates for a specific purpose.


The M47 with [email protected] was penetrated by the 88mm/L71 out to 250m but it only had 210 BHN armor.


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## delcyros (Jun 12, 2014)

Which is entirely possible if that plate contained flaws such as, f.e. laminations.
Remember, it´s not about hardness, it´s about flaws in the plate. While it may be possible to make flawfree plate in this thickness region (around 4"), even treated to relatively high hardness levels, if the attack is obliquily chances increase that the plate doesn´t behave ductile but brittle thus, softer plates are preferable.
However, that doesn´t mean that a soft plate automatically is flaw-free. For me, it appears that the T54 glacis plate was flawfree (still relatively high hardness level), while both the IS-2 plate (600m, harder) a the soft M47 glacis plate (200m, soft) were not.
The relatively closer distance of penetration of the M47 plate vs that of the hard IS 2 glacis can be used as an indication for softer plates being indeed ballistically better in this specific application (against capped AP).
I think that the exact opposite has been claimed instead.


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## Mobius (Jun 12, 2014)

The US examined a JS-II and measured the armor hardness.
http://www.dtic.mil/dtic/tr/fulltext/u2/011426.pdf
One odd thing is that while the front plate lists the BHN as 444 the tensile strength is equivalent to 295 BHN.

Then there's this:
http://tankarchives.blogspot.com/2014/06/is-2-modernization.html

I guess no flaw in that JSII armor.


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## delcyros (Jun 12, 2014)

> I guess no flaw in that JSII armor.



Several russian authors noted "bubbles" in cast elements, which are flaws. This has also been rported from israeli studies on JS-3. Not sure about the 100mm (or 90mm?) RHA elements, which replaced the 110mm/100mm cast ones in the final JS-2, though.



> One odd thing is that while the front plate lists the BHN as 444 the tensile strength is equivalent to 295 BHN.


It is possible, that only the surface was hardened, probably by additional heat treatment. Itï¿½s then kind of face hardened (but not true, as there is no ski-ramp like change in hardness gradient in the section, just a thin, hardened surface with an abrupt drop to normal plate homogenious hardness levels, which under dynamicly applied impact force is guaranteed to be flawed.
High hardness / high tensile strength doesnï¿½t add materially in ballistic resistence at 60 deg.

It may still have benefit in breaking up projectiles, particularely at high obliquity impact (by projectile damage), which may be desirable.
The basic problem is that ductility corresponding to 295BHN is simply to low to facilitate effective deflection properties (without going into to many details, the problem is worse for smaller calibres than for bigger ones due to the difference in impress exposure size and plastic deformation limits encountered). Rather, it will cause regularely some kind of shatter (even hard AP-caps donï¿½t work in 60 deg obliquity range), which may turn a sharp pointed penetrator into a blunt one, or in other words, a penetrator which is much better able to penetrate obliquily...

f.e. the KTï¿½s 55 deg sloped 150mm glacis plate may also contain flawed elements (difficult to manufacture thick homogenious plates without center plate sections differential cooling issues avoided) but it was thick enough that even with existing flaws it acted minimum like a 100mm unflawed, high quality plate, which at this obliquity is virtually proof against then existing weapons (unless previously damaged).

Nose breakage /nose shatter is a desirable aspect at low impact obliquity, where the required striking velocity goes up in a shattered projectile (by roughly 1/3), but it represents an entirely undesirable feature at high obliquity impact, where nose breakage would reduce necessary striking velocity to perforate armour- and greatly reduce to probability of ricochet in the first place (blunter penetrators have better biting angle).


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## stona (Jun 12, 2014)

All I know is that a French '75 is a killer cocktail 

I'll get me coat.

Steve


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## kettbo (Jun 12, 2014)

All the science and number-crunching! Good reading, but in the field, only rough ideas. Much of what gets penetrated, or not, can be influenced by compound angles (armor angles AND angle of the target to the angle of the gun as well as the hull angle to the horizontal due to terrain). Add some stowage on the tank, "smart" stowage aka goodies purposefully placed, track section, road wheels, and the like. 

T-34. Decent gun but the fighting effectiveness was limited by the vehicle commander also being the gunner. GREAT armor for the wt by late 41 standards. This armor advantage was surpassed by the Germans fielding better and more guns. But what the Germans could field, the Russians were able to field many times over and in places the Germans had little heavy forces to counter with. Better was the T34/85 with the 3-man turret and the more useful 85mm gun. On par with the US 76 and broadly close to the PaK40 in penetration, the 85mm gun had more useful HE round for BREAKTHROUGH.

NOT A SINGLE US Sherman that landed in NORMANDY was armed with the 76mm gun! All were at the depots in England, refused by the Armored Divisions. I do not recall the number present/sitting at the depots, but I seem to recollect 250-400 units. One must ask WHY? The first reason was that the 75mm gun had done well so far. Most of the combat was against infantry or strongpoints where the 75mm HE round was vastly superior to the US 76mm HE round. Another factor was Intel! Part of this was US believing the Panther was of limited production such as the Tiger I. I believe it was not long before D DAY that the alarm as sounded that the Panther was actually is wide-scale production.

Let's talk Sherman Firefly. At Normandy and until late war, only 1 in 4 were Firefly conversions. Then consider the all-powerful 17pdr had some bad ammo lots early-on. Some rather embarrassing results at a test shoot in Normandy. You cannot penetrate what you cannot hit! Once this was sorted out, a very respectable performer. Firefly tanks were a priority German target indeed. The 17pdr AT gun was less successful as the size and weight limited mobility.

Consider the lower rate of fire for some of these big guns and or slow traverse rates. Consider the reliability, mobility, and quantity. Tanks are no good unless they are running and fully-mission-capable. They are not good if stuck in the mud, have a busted final drive, or out of fuel! Must shoot, move, and communicate!!! On a tank, it is the package of all the characteristics. The big wild card is crew quality, training, and tactical sense. From the Operational Commander, down to the BN Cdr, Co Cdrs, PLs, vehicle commanders and the vehicle DRIVER! Taking on the COMBINED ARMS concept, lots of tactical air power and artillery make up for not having great tanks.


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## RCAFson (Jun 12, 2014)

I was reading some media articles about D-Day. One of the things that saved the US Army's bacon in Normandy was the fact that the vast majority of German tanks and armoured divsions were concentrated against the Commonwealth forces, to prevent a breakthrough around Caen. This rather fortuitously allowed the US to escape the worst consequences of having such poor AP weapons on their tanks.


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## delcyros (Jun 13, 2014)

> T-34. Decent gun but the fighting effectiveness was limited by the vehicle commander also being the gunner. GREAT armor for the wt by late 41 standards. This armor advantage was surpassed by the Germans fielding better and more guns.



High hardness armour plate works best in wrecking up the projectile (even hard capped ones) in the obliquity range 25 to 45 deg. There is still a bonus against shattered projectiles in this obliquity range, albeit much smaller than the 1/3 generated by shatter against vertical impact. Thus, the way, the soviets employed armour on their T34 was effectively canceling the older capped AP-shell used by the germans then. However, the solution was not -as often believed- the introduction of larger or longer barreled guns but instead 

[1] a significant improvement of the APCBC shell, which resulted in a virtually indestructable projectile (HE-filler reduced, more blunter noseshape of 1.1crh, composite welded nose, sombrero shaped AP-cap with better biting angle hardened all the way through), and 
[2] the adoption of APCR for existing 5cm KWK/PAK.

While [2] was an interim ad hoc solution to the problem, [1] was a necessary precondition before longer barreled guns (5cmL60, then also 7.5cmL43/48) could be employed at all. Raising the striking velocity didnï¿½t improved penetration unless the projectile was improved so much as to cope with the larger dynamic impact forces.
[2] also effectively countered high hardness and face hardened (more like poor quality Harvey hardened akin...) armour plate employed by the SU tanks. The low ductile, high hardness armour plate only works if it succeeds in messing up the projectile (nose shatter or breakage) at this obliquity range, if it fails to achieve this, the lower toughness (less ductile under impact) works against the plate. It was good when introduced but once improved APCBC -which were virtually immune to nose damage in mid obliquity- were issued in 1942/3, the T34 armour turned into comparably poor protection, even against projectiles from guns it previously defeated.


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## Mobius (Jun 13, 2014)

I got this from tank.net a few years ago. Aberdeen tests of 88mm/L71.


> Compare it to the 88 projectiles for 3000 + velocities vs targets.
> 8" [email protected] 0°:Two complete (NBL) penetrations with projectile passing through plate. 3124mv and 3257 mv.(550y/90y) Two ABL penetrations. Projectiles Intact. 3001 mv 3038 mv. (990y/860y)
> 
> 6 1/16" [email protected] 30°:Two complete penetrations, projectile through plate. Projectile intact 3008 mv 2971 mv (974/1100y)
> ...


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## pbehn (Jun 13, 2014)

kettbo said:


> All the science and number-crunching! Good reading, but in the field, only rough ideas. Much of what gets penetrated, or not, can be influenced by compound angles (armor angles AND angle of the target to the angle of the gun as well as the hull angle to the horizontal due to terrain). Add some stowage on the tank, "smart" stowage aka goodies purposefully placed, track section, road wheels, and the like.
> 
> T-34. Decent gun but the fighting effectiveness was limited by the vehicle commander also being the gunner. GREAT armor for the wt by late 41 standards. This armor advantage was surpassed by the Germans fielding better and more guns. But what the Germans could field, the Russians were able to field many times over and in places the Germans had little heavy forces to counter with. Better was the T34/85 with the 3-man turret and the more useful 85mm gun. On par with the US 76 and broadly close to the PaK40 in penetration, the 85mm gun had more useful HE round for BREAKTHROUGH.
> 
> ...



watching a documentary on Normandy there was a tank veteran who said his group of 150 tanks used 500 during the campaign to maintain that 150 at the front.


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## delcyros (Jun 15, 2014)

Mobius said:


> I got this from tank.net a few years ago. Aberdeen tests of 88mm/L71.



Yes, that demonstrates the problem. A projectile encountering itï¿½s critical velocity (each plate-projectile-obliquity combination had itï¿½s own crit velocity) will suffer breakage but here the breakage is increased by trying to establish the limiting velocity for perforation. Under those conditons, where the projectile is subject to severe forces acting on it for a longer time period, damage is typically most severe. Once You increase the impact velocity, projectile breakage again ceases and the penetrator makes it through intactly.
Shatter, however, does not cease. Even with meteoric striking velocity, the projectile wonï¿½t make it through intactly.
I have seen (and I believe previously referred to here) pictures of 7.5cm Pgr.39/1 penetrating a 2 2/3 calibre strong homogenious plate (67 kg/mm^2) at 30 deg with virtually no nose damage. These projectiles were optimised for obliquities around 15 to 40 deg, and unlike older projectiles didnï¿½t suffered any damage. The 7.5cm was optimised for even higher obliquities.

Sometimes it is more useful to use relative cal/plate ratioï¿½s instead of absolute figures. The Aberdeen trials for 8.8cm show
that it perforated

2.4 cal homogenious armour at 0 deg and (mean of) 940m/s -intact
1.8 cal homogenious armour at 30 deg and (less than) 918m/s -intact
1.5 cal homogenious armour at 45 deg and (about) 1002m/s -projectile damage starts
1.0 cal homogenious armour at 55 deg and (mean of) 1013m/s -projectile damaged

Using the 7.5cm Pgr.39/1 curves in cal/plate ratioï¿½s we attain the following data:
2.5 cal homogenious armour (70kg/mm^2) at 0 deg and (~) 940m/s -intact
1.9 cal homogenious armour (80 kg/mm^2) at 30 deg (~) 920m/s -intact
1.3 cal homogenious armour (100kg/mm^2) at 45 deg (~) 1000m/s -intact
-no data for 55 deg but at 60 deg:
0.9 cal homogenious armour (110kg/mm^2) at 60 deg (~) 1015 m/s -damaged

As can be seen, the 8.8cm is able to penetrate slightly more armour (relatively spoken) than the 7.5cm, thatï¿½s due to a much fine nose shape (1.47 crh as opposed to 1.1crh for the 7.5cm). However, the way these trials are tabulated hide the fact that the 7.5cm is actually better able to negotiate obliquity, particularely softer plates. The blunter nose shape would make penetration at low obliquity against soft armour (70kg/mm^2 plate, see above) more difficult (requires penetration by plugging) than the 8.8cm but soft armour plate would be more easily overcome at high obliquity. I donï¿½t know which plate hardness was used in Aberdeen but I strongly suspect that the 8" plate was harder than 70 kg/mm^2 used in german trials for this thickness range. Unfortunately, the trials then shifted to high hardness plates at higher obliquity (100kg/mm^2-110kg/mm^2, see above) and as long as the projectile stays intact (slight nose damage acceptable), a finer nose shape WILL STILL PERFORATE better by drilling action against hard plate (only, against soft plate, the blunt nosed ones are significantly superior). This is explainable by the failure mode of the armour plate. For homogenious armour it has been established on the prooving ground that higher BHN plates result in larger normalization than softer plates as measured by the perforation channels (at least in smaller calibre trials, 20mm model shot, 37mm and 75mm). 







The 1.1crh 7.5cm is -however- able to negotiate higher obliquity conditions more intactly than the 1.47 crh 8.8cm Pgr.

Normalization depends on two aspects:
[A] Nose shape and nose coverings of the APCPBC (hood effect, cap effect, nose shape)
* hardness of the target plate (the harder, the more normalization, but itï¿½s like the back hardness which counts in face hardened types of plates)

Coming back to the IS-2 obr. 44 glacis: 
The 100mm cast high hardness plate is -despite an angle of 60 deg- particularely vulnerable to 8.8cmL71 firing APCBC (and APCR) -narrowly within the performance envelope, even without flaws -around 110 to 120mm would be required here instead to secure immunity.
The 90mm medium hardness RHA plate of final IS2 would be better suited to defeat 88mm, 1.47 crh APCBC (though lower hardness plate would be preferable) and still be sufficiently strong to defeat the 75mm APCBC -unless flawed.

The adoption of blunt nosed 8.8cm projectiles was under consideration in 1945. Krupp reported that 8.8cm APCBC with 0.97 crh nose shape yielded excellent results. Further improvement could be attained by adopting sheath hardeneing technology for the projectile body instead of the cheaper decrementally hardening prefered for manufacturing reasons. Sheath hardening was known and used since the mid 30ï¿½s for Kruppï¿½s navy projectiles, like L4.4 20.3cm APCBC. Sheath hardened projectiles could practically get rid of the armour piercing cap and stay intact (APBC) and at 60 deg obliquity would yield an increase in perforation capability vs the 1.47crh Pgr.39/1 which is roughly proportional to the relative mass of the deleted cap.
These modifications would have kept the 88mm effective vs even the improved glacis of IS-2 (final design) and IS3, manufactured 1945.


edit:

I have extracted the relevant graphs from the Lilienthalreport 166 which demonstrate how the plate hardness change ballistic resistence of plates depending on obliquity. For better readability I have deleted out the 3cm L5 projectile and cumulated both original graphs into a single one. These trial plates (50kg/mm^2 mild steel and 145-150kg/mm^2 ultra hard armour steel) were of very high quality and generally flaw-free. Note that while there is -using the 30mm shot example- about 82% benefit in penetration of mild steel compared to specially hardened armour grade steel at vertical impact (90 deg), the difference at 30 deg impact would be entirely canceled out -the specially hardened plate is no better than mild steel!






This is important for glacis plates. Attention paid to make very hard plates for glacis plates were entirely wastes of effort. Just extrapolate the curves by mk1 eyeball and guess what happens at 20 deg. Hard plates would then be entirely at ballistic disadvantage compared even against mild construction grade steel. Also, pay attention to the differences between 20mm and 30mm shot. The point of crossover moves. For the 20mm it would be at 27 deg, while for the 30mm it is at exactly 30 deg. I have limited data for 75mm which seem to suggest about 35 deg as point of crossover. 
We can call this effect "inverse scaling". I stumbled over the effect when I tried four years ago to verify whether or not scaling is dependent on obliquity in another context. 
Right now I can confirm it for various projectile sizes of the same family. 2cm and 3cm AP,
75mm and 88mm Army APCBC; 15cm and 28.3 cm Navy L3.7 APCBC and finally 20.3cm, 28.3cm and 38cm Navy L4.4 APCBC (where the point of crossover is at between 60 and 55 deg, btw).
What is known as scaling effect, the loss of quality of plate when the absolute calibre is increased (but the relative plate/cal relation stays the same) is only true at vertical impact and becomes inverse at very high obliquity.

Consequently, cast high hardness armour grade material for the glacis of IS-2 obr. 44 is likely not offering the degree of mild steel if engaged by 88mm at 30 deg, too.


edit: apologies for the technical -and sometimes not so easy to understand reply. English isn´t my primary language but I hope its possible to follow the reasoning explained herewith.*


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## Mobius (Jun 15, 2014)

Is that resistance in terms of any particular type of penetration? And how would it be tested?


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## delcyros (Jun 16, 2014)

Mobius said:


> Is that resistance in terms of any particular type of penetration? And how would it be tested?



Not exactly sure what precisely You mean here. I take it that You mean the resistence of plate to penetration at obliquity impact?
If so, the resistence was inferred by the Gnot -the necessary velocity to defeat said plate by a given projectile according to the guidelines for prooving ground trials which may be found in BIOS report 1343, item No. 2 "German Steel Armour Piercing Projectiles Theory of Penetration", dated sept. 1945, including the summeries of the minutes from the meetings of Berlin 1943 and Hillersleben 1944. -particularely, "Methods of staging and conducting trials" ,p.19-26 in said document.


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## Mobius (Jun 16, 2014)

delcyros said:


> Not exactly sure what precisely You mean here. I take it that You mean the resistence of plate to penetration at obliquity impact?
> If so, the resistence was inferred by the Gnot -the necessary velocity to defeat said plate by a given projectile according to the guidelines for prooving ground trials which may be found in BIOS report 1343, item No. 2 "German Steel Armour Piercing Projectiles Theory of Penetration", dated sept. 1945, including the summeries of the minutes from the meetings of Berlin 1943 and Hillersleben 1944. -particularely, "Methods of staging and conducting trials" ,p.19-26 in said document.


That answers my question. According to the BIOS report the German criteria is "To qualify as a successful penetration the projectile was required to penetrate the plate in a condition fit to burst and not to deform in any manner which would prevent detonation." So a different criteria like 50% of the mass behind the armor or some witness plate behind armor penetrated would produce quite a different relationship between angle and armor resistance graph.


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## delcyros (Jun 16, 2014)

Mobius said:


> That answers my question. According to the BIOS report the German criteria is "To qualify as a successful penetration the projectile was required to penetrate the plate in a condition fit to burst and not to deform in any manner which would prevent detonation." So a different criteria like 50% of the mass behind the armor or some witness plate behind armor penetrated would produce quite a different relationship between angle and armor resistance graph.



Indeed. However, if You look into Navy and Army APCBC penetration graphs, the performance against homogenious armour is often labelled with:
"gegen Homogenpanzer bleibt das Panzergschoï¿½ in der Regel heil, Grenz- und Heilbleibkurven fallen zusamenn"

Which means that the seperately drawn curves for intact projectile penetration and projectile penetration in either broken condition or intact but embedded in plate for very hard armour (incl, face hardened) are usually falling together for homogenious armour, which means that the projectile, even while stuck in the plate -where damage done to the projectile is typically most severe- would still be in effective bursting condition (whole or scratched, some other damage was also accepted: nose breakage and projectile set up as long as it didnï¿½t reach the cavity). Normal 7.5 and 8.8cm projectiles would require 5 out of 5 projectiles to pass the plate in effective bursting condition at stated velocity. But note that in the trials, only blind filled APCBC were used, no life projectiles! Assertion whether or not the projectile received sufficient damage was kind of subjective based upon examination of the recovered projectile body and particularely, whether or not projectile damage reached the explosive cavity or deformed the base fuse plug.

At high oblqiuity different thing may happen. The highest obliquities systematically tested for in ww2 Germany were 60 deg and 75 deg impact. At these obliquities, base damage was a frequent occurance (no cap could protect from it), and nose breakage was normal. Eventually, the acceptance trials were thus carried out to 45 deg, where base damage didnï¿½t regualely set in for proofing and manufacturer acceptance purposes.

But remember, what You call "armour resistence graph" is actually only a graph for the G-grenz penetration at fixed striking velcoity (simulating 100m distance in the example above), comparable more or less to US NBL definition at obliquities larger than 45 deg ( US Navy EEF definition at obliquities lower than 45 deg). Resistence of armour is our interpretation by comparing the respective penetration in very much hardened plates (150kg/mm^2 tensile strength) with those of construction grade steels (50kg/mm^2 tensile strength).


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