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M3 75mm penetration?


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I just got bunch of combat missions. I had only CMBB of cmx1, now also have CMAK and CMBO

Now i have questions.

First of all, why is in each game penetrations slightly different?

Second, CMBB and CMBO have some nice standard penetrations. But for some reason I think that CMAK have some serious overpowered guns, specially on American side. What the hell is a 75mm M3 pierce over 80mm at 1000m or more? What hell is this? Where did they base this on? Also at 100m it pierces more 100mm, what is going on?

Even 76mm M5 goes trew more armor than it should.

Its this for balance? I tough was suppost to be realism...

CMBO and CMBB have both nice penetrations, whats up with CMAK?

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But that doesnt make any sense. The M3 gun was outdated against panzer IVs.Because all books ever read, said the M3 was already outdated against 80mm thick armor such as tiger side and back armor and stug frontal armor and panzer IV hull.

Even wiki says so(I normally dont tend to guide trew it). "80mm thick was enouph to to take serious threat from 75mm M3 and 76mm F34 gun". What the hell? The german tests proove that as well, in a 60degree angle it has to come with 100m too pierce 80mm.

Wikipedia: "Against earlier-model Panzer IVs, it could hold its own, but with its 75 mm M3 gun, struggled against the late-model Panzer IV (and was unable to penetrate the frontal armor of Panther and Tiger tanks at virtually any range).[96] The late-model Panzer IV's 80 mm (3.15 in) frontal hull armor could easily withstand hits from the 75 mm (2.95 in) weapon on the Sherman at normal combat ranges,[97] though the turret remained vulnerable." Sources taken from Jentz & Doyle

"The 80mm-thick frontal armour of the Pz.Kpfw.IV was capable of withstanding attack from AP shells fired by Russian T-34/76 and American 75mm M3 gun." Hillary Doyle & Tom Jentz in New Vanguard Panzerkampfwagen IV Ausf.G,H and J 1942-45

Wa Pruf claims the following:

M4A1/3 penetrates pzIVH at ranges up to: 100m on hull (even tough it is based on 60degrees from horinzontal or 30 degrees from vertical)

Plus, like I said before, in each combat mission game theres different penetration from each gun. I mean like Panzer IV has slightly different penetrations in each game.

Also why do the soviets have bad penetrations with their M3 and 76mm american gun on CMBB?

"As shown in penetration Range Tables 1,2 and 3, // Pz.Kpfw.IV with 7.5cm KwK40 was superior to the american M4 medium Tank with 75mm M3 and the Russian T-34/76."

And many more. In CMBB everything works out fine, now I have looked deep into CMBO and also its still kinda wierd and in CMAK aswell. I find panzer IVs being defeated all the from front all normal combat ranges.

Dont take me wrong, im not saying its overpowered for real, just saying it looks, and I would like someone to show me this is correct.

By the way, what was the M72 Shot used for?

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There have been several huge threads on guns and armour penetration on both CMBB and CMAK forums so I suggest you read these as your point is probably already been answered.

The most important thing missed by most is that ammo eveolved throughout the period so depending what date you are referring to may have a different penetration than an ealier or later date. Also bear in mind armour quality changes during the war and also 80mm of rolled armour is not the same as 80mm of cast armour.

So for for every date if you would just like to roll together the type of cap on the shell, the armour type , the quality of armour, plus the angle, and of course compensating for rising and falling shot, then you will get an approximation.

I have many military books but they all refer pretty much to the same information which of course was carried out at a point in time and therefore had no hope of being the last word on the matter - they could only report on what happened in their trial.

I would just play the game and enjoy it for what it is. I am sure CMBN will improve on CMAK.

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80mm fronts of Panzer IVs were never "proof" against either Russian 76mm or the Sherman M3 75mm. When the latter was using uncapped ammo it had comparable performance to the Russian 76mm, and both could be defeated by the 80mm flat plate on Panzer IV hulls and StuG fronts, beyond close range - about 400-500 meters. But at close range the 80mm front was not sufficient protection, and German accounts themselves state that 80mm front provided "no protection" from Russian tank guns inside 500 meters.

With improved APCBC ammo in the late war, the performance of the Sherman 75mm improved considerably against these plates. The German armor was face hardened, but that provides little benefit against properly capped ammo.

Sherman 75s with capped ammo could also defeat the Tiger I side, which was specified 80mm but frequently more like 82mm thickness and higher quality plate than that found on the more common Panzer IVs and StuGs. Similarly, Russian 76mm using BR-350B (capped but not ballistic capped, but an improvement over the early war BR-350A which wasn't capped at all) did defeat such plates at point blank range. The Russians also developed APCR (tungsten core "sub caliber") ammunition for their 76mm guns, fielded it in 1943 and abundantly in 1944. Which could readily penetrate 80mm flat plate to middling combat ranges.

Comments about Tiger I fronts or Panther fronts are beside the point; all are well over 80mm.

The late model long Shermans (76mm W armor "easy eights" for example) were clear superiors to the vanilla Panzer IV. Once they had the W or W+ armor configuration, they could withstand the higher velocity German 75mm if it hit the glacis, beyond a range of about 750 yards. Either could kill with a turret hit. The long 76mm Shermans could penetrate the Panzer IV easily, any plate and any aspect, to twice that distance.

The long 76 using plain APC, early, had trouble against Tiger I fronts and Panther turret fronts beyond about 400 yards, due to "shatter gap" effects - the round had sufficient energy to penetrate out to more like 1200 yards, but the shell could not take the stress of the impact and broke up instead, in roughly the 500 to 1000 yard window - the "shatter gap". The solution was APCR tungsten core ammo, which did the job no problem. Only the Panther glacis could withstand a hit from one of those (due to high slope, which works best against high velocity sub caliber rounds).

In short, you are reporting irrelevant items (about plates way thicker than 80mm) or reports about earlier versions of the attacking weapon (uncapped early US 75mm or Russian 76mm BR-350A). To assess a single report, it must relate the proper target, attacking gun, specific round fired by that gun, and the range. Without the round or the range, it will be misleading.

Note that in Russia or North Africa, where engagement distances were typically pretty long (800 to 1000 meters or more), protection outside of 500 meters was a huge advantage. Fighting in a Normandy hedgerow, it was irrelevant - initial LOS was likely to be more like 200 meters.

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whats the difference between 80mm rolled armor v 80mm cast armor(penetration)

It is more a matter of consistency, rolled armour will tend to be more even through out. Cast armour will tend to be not so uniform.

Cast armour however can me moulded more easily into smooth shapes which can have better deflection qualities.

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Can I recommend Google. The site where this quote comes from turns up on the first page of my search. I have to say I think it is a very comprehensive view provided:

Armour Hardness and Quality

Armour hardness and quality is vitally important when comparing different weapons and often seems to be overlooked. To show why it is so important one example will be given. The Italian Breda 20mm gun had about the same penetration capability as the German 20mm Flak guns. However the tabulated data shows the Italian gun to have a penetration of 28mm at 500m range against a 0° target plate, whereas the German gun has a penetration of only 14mm under the same conditions. Other ranges show similar discrepancies. The reason is because the German gun was tested against a relatively hard armour plate with a BHN of 435 to 465, whereas the Italian gun was tested against an armour plate with a BHN of only 210 to 245. Source: Jentz, Thomas L: Tank Combat in North Africa.

Most of the information that follows comes from Robert Livingston and I am grateful to him for answering my many questions about this subject.

Measurement of Armour Hardness

Armour hardness is usually given by quoting the Brinell Hardness Number (BHN). A Brinell Hardness Test is conducted by pressing a tungsten carbide sphere 10mm in diameter into the test surface for 10 seconds with a load of 3,000kg then measuring the resulting depression. The BHN is calculated according to the following formula:

BHN.gifCopyright © 1995 John C. Russ.

Several BHN tests are usually carried out over an area of armour plate. On a typical plate each test would result in a slightly different number. This is due not only to minor variations in quality of the armour plate (even homogenous armour is not absolutely uniform) but also because of the nature of the test which relies on careful measurement of the diameter of the depression. Small errors in this measurement will lead to small variations in BHN values. As a result, BHN is usually quoted as a range of values (e.g. 210 to 245, or 210-245) rather than as a single value.

The BHN of face hardened armour uses a back slash ‘\’ to separate the value of the face hardened surface from the value of the rear face. For example, a BHN of 555\353-382 indicates the surface has a hardness of 555 and the rear face has a hardness of 353 to 382.

Another test for BHN uses a Poldi hardness tester. The Poldi portable unit relies on a hammer blow impression in a standardised sample. This test is less accurate than the Brinell Hardness Test. When there are widely different values for quoted BHN (greater than the normal differences described above) then the cause may be use of a Poldi hardness tester instead of the Brinell Hardness Test.

There are other ways of measuring hardness. The Brinell Hardness Test may be carried out with a different load or type of sphere which will produce slightly different numbers. The Brinell Hardness Test described above is called “HB 10/3000 WC” and was the type of test used by the Germans in World War II. Other types of test include the Vickers Hardness Test and the Rockwell Hardness Test. Each type of test measures resistance to deformation of material in slightly different ways. Conversions between different hardness scales are therefore only approximate but they are useful and so are presented in the Steel Hardness Conversion Table.

Types of Armour

There are two main methods of manufacturing armour: rolled homogenous and cast. Rolled homogenous armour can then be further worked to produce face hardened armour. There are two main methods of securing the parts of the vehicle together: by using fasteners such as rivets, and by welding.

Rolled Homogenous Armour

Rolled homogenous armour (RHA) is essentially cast metal which has been further worked and shaped, aligning the grain structure of the metal and thus increasing its ballistic strength. It is made by first pouring molten metal into moulds and allowing it to cool and solidify into ingots. These big barrel shaped pieces which come out of the moulds are pounded with giant hammers to form billets which are then rolled at the rolling mill to become slabs. The rolling mill uses tonnes of pressure on a wide roller above and another below the red hot steel slab. The slab is rolled many times, in at least two perpendicular directions (cross-rolling), until the desired thickness is achieved.

The steel must then be hardened. It is re-heated to the transformation temperature (above 800°C) and plunged in water. The rapid cooling works molecular changes so that the steel becomes very hard, providing the alloy content is correct. It is then reheated to just below the transformation temperature and cooled again. This last step is called tempering and reduces the hardness while greatly increasing the ductility. The steel is now called rolled and homogeneous, that is, it has been shaped by rolling and the molecular structure is generally uniform throughout the cross section.

Face Hardened Armour

Face hardening (FH) is a method used to increase the armour hardness of the surface of armour plate. The rear side of the armour plate remains at its original hardness. Face hardening is carried out by taking a slab of RHA and heat treating it again, but on one side only. The heat treating is time consuming and results in a warped plate which must then be flattened in large presses. The Germans were able to handle plates up to and including 50mm thickness (with production oversizes up to 55mm), and tried 80mm FH on the early Panther glacis. Later on the Germans found a way to use a heavy electrical current flow through the steel to induction-harden one face. Both methods were used until the end of the war.

The purpose of the hardened face is to shatter an incoming projectile’s head before it can penetrate. The Germans found it resisted Soviet uncapped AP and APBC projectiles quite well, when the armour plate thickness was around the same size or not too badly overmatched by the projectile (such as Pz.Kpfw.IV 50mm front armour vs. Soviet 45mm or even 76mm AP or APBC). Britain and the USA tested projectiles against FH armour as a matter of course until about 1943, but rarely used it on production vehicles because of its relatively poor resistance to German APCBC in comparison to RHA. The Germans were faced with APC and APCBC from the Western allies only, not the Soviets, so their decision to use FH armour weakened their tanks against Western guns but strengthened them against Soviet guns.

Cast Armour

Cast armour is made by pouring molten metal into moulds which are shaped as the required vehicle component. After removing from the moulds the rough spots, risers and gate marks are ground off and the component is heat treated. Heat treating consists of heating, quenching (rapid cooling in water) and tempering as described for RHA. Cast armor is never worked or squeezed down into thinner form as rolled armor is, therefore it has an inferior grain structure and lower ballistic resistance.

Cast armor is always homogeneous and was never face hardened (apart from a few experiments). The difference in hardness between the outer surface and inner surface found on some cast armour is more a result of poor heat treatment or insufficient alloy content than any intentional effect intended to increase ballistic resistance. Homogeneous armour works best when it is the same hardness throughout, as changes in hardness form stress concentration boundaries which significantly degrade ballistic resistance.

Cast armour resists less well than rolled armour of the same hardness and thickness. USA tests of production quality armour in 1942 and 1943 showed this clearly, in which 51mm (2 inch) thick test pieces of cast armour showed a 15% to 20% inferiority compared to 51mm (2 inch) rolled plates when hit by 75mm projectiles. The tests also demonstrated that rolled armour can be raised to higher hardness levels than cast armour without losing ductility, and therefore ballistic resistance.

Riveted and Welded Armour

There are two main methods of securing the parts of the vehicle together: by using fasteners such as rivets, and by welding. The strength of the joins is the same, but when riveted armour is hit by a projectile the rivet heads tend to shear off and fly around the interior of the tank causing damage to the interior of the vehicle and injury to the occupants. This occurs even if the projectile is not powerful enough to penetrate the armour. Welded armour is better because it does not suffer this extra damage when hit by a non-penetrating projectile.

Flaws in Armour Plate

To complicate things even further, some armour plates were flawed which significantly affected their ballistic resistance. The only way to determine the presence or absence of flaws is to sample the steel in question and run metallurgical tests. By deduction, premature ballistic failure as recorded in field tests indicate the presence of flaws, such as the several tests of captured Panthers which had poor quality glacis plates (which includes the report of tests of Soviet 100mm and 122mm guns against a captured Panther at the Kubinka Proving Ground found in the library at the Russian Military Zone).

It was determined reliably that a large proportion of USA armour, both cast and rolled, produced prior to November 1943 was flawed to such an extent that it resisted about 5% to 50% less than it should have (mean resistance around 85% of 1944-45 armour plate). Also British armour of greater than 57mm to 63mm was flawed until about 1944.

The BHN of steel is not directly related to flaws. Some Soviet T-34 BHN 450 armour was relatively flaw free, while other plates of the same thickness in the same tank were quite flawed, as shown by tests conducted by Watertown Arsenal in the USA.

For the technically minded: flaws are things like stringers, laminations, inclusions, and transformation by-products which are in dirty or improperly heat treated steel. Flaws also include crystalline microstructure, as opposed to the ductile microstructure of correctly made, sufficiently alloyed steel.

Determining Penetration Capability

There are three main factors which affect penetration capability and which must be taken into account when comparing gun penetration between different nations. While this section does not attempt to present a detailed analysis it does present some useful generalisations. The three main factors are: the hardness of the armour plate used as a target during testing; the quality of the ammunition used during testing compared to normal production quality; and the definition of penetration used for tests.

Hardness of Target Armour Plate

The hardness of the target armour plate used during gun ballistics tests must be taken into account when comparing gun penetration data. This usually varied considerably from country to country, and even for one country there were often different hardness standards used for different target plate thicknesses.

Target armour plate can be either RHA or FH and is made in the same way as vehicle armour plate. Test results for the USA and Britain often included both types of target plate, although results quoted on this web site are RHA unless otherwise stated.

Ammunition Quality Used During Testing

British Ammunition Quality

The British used ammunition of ‘calibration’ standard for testing, which was top quality.

German Ammunition Quality

The British Intelligence Objectives Subcommittee report German Tank Armour dated 1946 includes information that an approximate 5% to 10% deficit could be demonstrated by production quality ammunition compared to that used for testing.

Soviet Ammunition Quality

The ammunition quality used for Soviet testing is unknown. However Soviet quality control was generally poor and ammunition was substandard up until about 1944, which would degrade penetration in unpredictable ways. I would expect that this means that some ammunition would perform better than predicted and some worse, or even considerably worse.

USA Ammunition Quality

There is some evidence to suggest that the USA used normal production quality ammunition in tests.

Definition of Penetration

Even after the hardness of the target armour plate and the quality of ammunition used during testing are taken into account, there may be further apparent differences in gun penetration performance due to the way each nation carried out penetration tests. The definition of when a projectile penetrates an armour plate differs from country to country, and sometimes there is more than one definition for a particular country. It is most often defined as when at least half (sometimes two-thirds to three-quarters) of the projectiles fired at the target plate achieve ‘penetration’.

The trouble starts when trying to define ‘penetration’. For most countries this means the projectile has to completely pass through the target armour plate, however there were some variations to this; e.g. for British 2 Pounders only 20% of the projectile had to pass through (but it had to do so on 80% of occasions instead of 50%).

Another complication is that there was different criteria to measure the quality of armour plate used for the production of armoured vehicles, than the criteria used to measure gun penetration performance. In the first case the tests determine how much protection an armour plate can provide under all conditions, and the criteria used is usually when the plate first starts to fail. On the other hand when measuring gun penetration performance the purpose of the tests is to establish what penetration could be expected, on the average, for that particular ammunition type. The two criteria used would obviously be very different.

It doesn't help matters that in the USA one definition is called the ‘Army’ criteria and another is called the ‘Navy’ criteria. For a while there I had naively assumed that one critieria was used to measure the performance of Army projectiles, and the other for Navy projectiles. However this is not so, in fact all USA gun penetration performance is assessed to the Navy criteria regardless of the service arm actually conducting the test. Silly me.

It is sufficient to say that although each country has slightly different definitions of penetration, these effect of these differences is usually small. The British W/R limit criteria (in general use by 1942) and USA criteria are essentially the same and have negligible differences. German criteria may be slightly higher by 0% to 2%, however any difference is slight and may not be statistically meaningful. The Soviet criteria is higher than the British and USA criteria by a small amount, 2% to 3%. The result of this higher criteria is that the gun data tables indicate a lower penetration under the Soviet criteria than compared to the USA criteria.

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  • 5 weeks later...

I realize I'm a month overdue in reacting to this thread, but there's too much in here goading me to bite.

The M3 gun was a decent tank gun when it was taken into service. The ammunition, however, wasn't up to the task. It was fed old SAP ammo, which turned out to shatter on 30mm FHA in a number of cases. This was a known problem, according to the papers from the Cairo ballistic tests. The M61 was meant to replace the SAP with a more robust projectile. In tests this worked fine, but in the field the Germans turned out to shrug off hits which should have penetrated easily. This turned out to be due to the projectile shattering on the armour.

The M72 was a more spartan design for a penetrator, sacrificing behind-armour effect to achieve greater robustness. It was meant as an interim round, until the M61 could be improved. (I'm unclear on whether this involved introducing a cap to the M61 or just improving on the one it had.)

When Tobruk fell to the British, they obtained a large stock of German 75mm AP shells, which they modified to be fired from Grant/Lee tanks. When fired from different ranges at captured Pz III's, it was noted that the German projectiles penetrated from farther, and their explosion behind armour was 'catastrophic'.

The 'new' M61 turned out to be much less prone to shattering, but I cannot find any reference which says that they actually started penetrating deeper.

While it is therefore true that the ammunition for the Sherman improved with time, it is still a gun putting out only 1.3 MJ versus the KwK40's 2.1 MJ.

On the other side: the Pz IV was not a battlefield heavyweight anymore when it faced the Sherman. Its chassis was arguably obsolescent by the time it got the KwK40, and there was hot strife in the OKW about turning all Pz IV chassis production into StuG IV's and JPz IV's. The reason the turreted Pz IV tank was produced at all after half 1943 was Guderians insistence upon it. His argument was that the StuGs could not fulfill the role of full tanks in armoured breakthroughs - which is true. In hindsight we can wonder if it wouldn't have been better. The StuGs were 'harder' against enemy fire than the turreted tanks, and the exploitations Guderian dreamt of hardly ever took shape after this point.

While it is true that the Pz IV had 80mm of armour on its front, this was compromised by many perforations for hatches, ports, and view slits. It had a much thinner turret front (50mm over half the front area!) than this 80mm figure. Even then, it was almost balancing on its front roadwheels. The Pz IVH wasn't impervious to fire from the Sherman, and the full Wa Prüf report bears this out. By '44, the IV was none too popular with the fighting men due to its overloaded suspension, compromised armour, and tendency to bog.

As to metallurgy of armour steel, I am tempted to write a great essay, but I doubt anyone would be interested in the nitty-gritty.

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