Best Tank Destroyer/ self-propelled gun

[delcyros]

I just give only what I have seen so far. The obliquity condition is never mentioned in the german avaiable primary sources.
There is nothing like a most effective BHN level for armour plates. The higher, the more stopping power it has. Diminishing returns for overhard plates exist in manufacturing constraints and britellness (esspeccially hydrogen embrittelment and cast armour) and the ductility against large calibre impacts (large starts with 8" and more), the latter hardly beeing a factor against tank guns.
A 200mm, 260 BHN plate has less stopping power than a 120mm BHN 300 scaled up to 200mm thickness of the same quality, if it would be possible to treat such a plate without quality loss wrt laminations and ductility, which is the limiting factor. Otherwise they would have produced them.

[glen]

7.5cm KwK42 L/70

Projectile weight: 6.8 kg (APCBC)
Sectional Density: 1.719
Muzzle Velocity: 935 m/s
Total Kinetic Energy: 2979 KJ
Kinetic Energy pr. cm^2: 67.43 KJ

7.5cm KwK40 L/48

Projectile weight: 6.8 kg (APCBC)
Sectional Density: 1.719
Muzzle Velocity: 790 m/s
Total Kinetic Energy: 2122 KJ
Kinetic Energy pr. cm^2: 48.03 KJ

67.43 / 48.03 gives a ratio of 1.40
106mm / 138mm gives a ratio of 1.30

ratio of KE=140%
ratio of actual penetration=130%

ratio of de marre=127%

De Marre's theory is more accurate.

Other examples:

50 mm KwK 38 L/42

Pzgr 39 (APCBC) 2.06 kg 685 m/s

55mm/30degree @100m

-------------------------------
50 mm kwk39 L/60

Pzgr 39 (APCBC) 2.06 kg 835 m/s

69mm/30degree @100m

ratio of KE=149%
De Marre ratio=133%
ratio of actual penetration=125%

De Marre's theory is more accurate.

75 mm KwK 40 L/43

Pzgr 39 (APCBC) 6.8 kg 740 m/s

99mm/30degree @100m
--------------------------------------
75 mm KwK 40 L/48

Pzgr 39 (APCBC) 6.8 kg 790 m/s

106mm/30degree @100m

ratio of KE=114%
De Marre ratio=110%
ratio of actual penetration=107%

De Marre's theory is more accurate.

75 mm KwK 40 L/43

Pzgr 39 (APCBC) 6.8 kg 740 m/s

99mm/30degree @100m
-------------------------------------
75 mm KwK 42 L/70

Pzgr 39 (APCBC) 6.8 kg 925 m/s
138mm/30degree @100m

ratio of KE=156%
De Marre ratio=138%
ratio of actual penetration=139%

De Marre's theory is more accurate.



You can compute more by yourself from this link:
World War II Tanks - Germany's Penetration Tables

[glen]

At Aberdeen the penetration performance of the 8.8cm KwK36 L/56 & 8.8cm KwK43 L/71 against vertical 240 BHN RHA armor at 100m was as follows:

8.8cm KwK36: 162mm
8.8cm KwK43: 232mm

ratio of KE=167%
ratio of actual penetration=143%
ratio of de marre=145%

De Marre's theory is more accurate.

Furthermore, the data shows that pzgr39-1 and pzgr39 share the same penetration. The little difference of penetration between these two projectiles can be ignored.

[glen]

Almost every German gun obeys De Marre's theory except for Kwk43, according to Russian and American test/ battle field performance, the kwk43's official score is quite strange....probably the reason is that German could NOT produce >150mm plate whose quality is as good as thiner ones, neither could Amrican or british or Russian. The thicker the plate is ,the more difficult to retain high quality.

[delcyros]

Glen, the De-Marre formula assumes solid AP-shots without cap for a very narrow range of T/D ratios and obliquities. Outside this envelope, the De-Marre formula shows results which some times work, sometimes don´t work, just like a monte carlo alike probability step system. You don´t want this condition to apply for Your question.

I fully agree in plate thickness and quality related issues. However, it could defeat 200mm plates. It´s true that 200mm are not "true" 200mm in stopping power but the 200mm it could defeat where usually of the same quality as those encountered in the battlefield. So the difference is of more theoretical interest, as it shows marked problems in calculations when applying the De-Marre formula. Never use it at T/D ratios above 1.0, differences may be fractions, but fractions are important.

When calibrating on 2420 fps striking velocity at 100m and 30 deg for the KWK 36, and assuming the projectile is with regards of it´s properties like a stand. US M79 AP, without cap and filler, the critical plate thickness at which it achieves full penetration is 4.7" at a relative quality of 1.25.
Comparing to a striking velocity of 3140 fps for the L71, I get a penetration of 7.2" single plate aequivalent of quality= 1.25 or 7.88" single plate aequivalent perforation of quality = 1.14.
BHN value for quality 1.25 = 280, matching requirements for 120mm plates
BHN value for quality 1.14 = 255, matching requirements for 200mm plates

Calculations performed with M79APCLC

best regards,
delc

I see no conflicting datas.

[glen]

the De-Marre formula assumes solid AP-shots without cap for a very narrow range of T/D ratios and obliquities.

You are right,and my supplement is that: T/D ratio should be around 1.0, it can be 1.2 while De Marre's result is still quite accurate. The hitting velocity should be less than 1200m/s otherwise both amor and projectile will fall to pieces and the remain part of projectile will continue to penetrate the amor other than "throwing back". That's why modern APFSDS is more effective than WWII AP when facing slope amor.

There is another important concept: When a projectile double its KE, it just can NOT penetrate twice thickness of same quality amor. That is to say, ONE 200mm plate's stopping power is quite bigger than TWO 100mm plates in spite of what type the projectile is (AP,APCBC, APCR etc.)With regard to multi-layer amors, we can't add up each amor's thickness simply in order to get the total stopping power.It's a basic knowledge.

Kwk43's APCBC KE has 67% advantage on kwk36's, therefore, kwk43's penetration must be LESS than 200mm@100m since 120*167%=200.
Delcyros, I agree that if kwk43 apcbc's penetration is 200mm@100m, the target plate of kwk43 must be different from kwk36's.

I've got the answer! The thick target plates (>150mm even >200mm) are of inferior quality compared to thin plates(<150mm), therefore, those mighty guns' (such as 17 pdr,kwk43 ...)score is overvalued inevitably. This can perfectly explain why those guns are not sufficient when facing Panther D's glacis (80-85mm/55 degree) which is equivalent to "good-quality thick plate"(>150mm).

LOL

[Soren]

No Glen, the thicker plates were NOT of worse quality! The BHN level was just lower, which is completely normal. QUALITY DID NOT CHANGE.

Against WW2 AP projectiles the best armor BHR was 255 - 265 BHN, the level of the Tiger Ausf.E's armor, the same armor which managed to stop 76mm & 77mm Allied AP projectiles at point blank range! Yet the 88mm KwK43 L/71 is capable of punching holes in this armor beyond 4 km if the thickness is 100mm! The KwK43 would punch through 100mm of 300 + BHN armor past 4km for crying out loud! The 122mm D-25T can hardly punch through 100mm of VERTICAL 240 BHN armor at 3km, the 88mm KwK36 L/56 being just ~10mm behind it.

And like Delcyros explains De marre's theory DOES NOT WORK for these projectiles! It works for solid shot AP projectiles, NOT APCBC, esp. not when slope is applied! The theory is from 1870 Glen! Not 60 years later when the APCBC projectile was introduced!

Also for the last time, the 88mm KwK43's APCBC projectile was designated Pzgr.39/43, NOT Pzgr.39-1, the 88mm KwK36's APCBC projectile was designated Pzgr.39-1!

Its time you get this into your head Glen, cause its getting really straining having to repeat it!

[Juha]

Soren
17pdr was also 76,2mm gun, and its APCBC round was definitely able to brew up Tiger I at medium ranges. Gordon's Firefly knocked out 4 Tiger Is in the battle in which Wittmann was killed and another Firefly brewed up 2 more, modesty claiming only 2 Pz IVs.
I also have seen too many photos of holes made by T-34's 76,2mm gun onto Tigers to take your claim too seriously.
That said IMHO Pz VI E was a good and effective tank but expensive to product.

Juha

[Soren]

I wasn't talking about the 17 pdr's APCBC projectile Juha, I was talking about its APDS projectile failing miserably at close range against the Tiger Ausf.E's armor. The US 76.2mm gun was even worse in this regard, WITH APCBC, as it often just shattered at point blank range. The US had previus to the introduction of the 76.2mm gun promised that it would be able to defeat the Tiger's front armour out to 1,000 yards, in actuality it wasn't even capable at 300m, much to the dismay of the US tank crews.

Now let me see just ONE single photo of a 76.2mm Zis gun having penetrated the front armour of the Tiger - you'll have a hard time finding one!

[Juha]

Soren
you wrote "Against WW2 AP projectiles the best armor BHR was 255 - 265 BHN, the level of the Tiger Ausf.E's armor, the same armor which managed to stop 76mm & 77mm Allied AP projectiles at point blank range!", so I took that included also side armour. All photos showing soviet 76,2mm penetrations I recall showed holed side armour of Tiger and usually there are a group of hits close to each other of which only one is a clean penetration. So clearly Soviet 76,2mm gun was hard pressed to penetrate Tiger's 82mm side armour. I only wanted to notice you that you made too sweeping claim. After all it's probably that the commonest reason to Tiger loss was hit/hits by 76,2mm AP round(s). Also in your message there wasn't a mention on APDS.
But I think we a not so far each other when we are talking on Tiger I, a very good but expensive AFV.

Juha

[glen]

Originally Posted by Juha

Soren
you wrote "Against WW2 AP projectiles the best armor BHR was 255 - 265 BHN, the level of the Tiger Ausf.E's armor, the same armor which managed to stop 76mm & 77mm Allied AP projectiles at point blank range!", so I took that included also side armour. All photos showing soviet 76,2mm penetrations I recall showed holed side armour of Tiger and usually there are a group of hits close to each other of which only one is a clean penetration. So clearly Soviet 76,2mm gun was hard pressed to penetrate Tiger's 82mm side armour. I only wanted to notice you that you made too sweeping claim. After all it's probably that the commonest reason to Tiger loss was hit/hits by 76,2mm AP round(s). Also in your message there wasn't a mention on APDS.
But I think we a not so far each other when we are talking on Tiger I, a very good but expensive AFV.

Juha

Soviet 76.2mm BR-350B projectile can penetrate Tiger side 82mm amor within 100-200 meters (Kursk battle), that's suicide range. With reagrd to more powerful BR-350P projectile, its service was after Kursk battle.

[glen]

Originally Posted by Soren

No Glen, the thicker plates were NOT of worse quality! The BHN level was just lower, which is completely normal. QUALITY DID NOT CHANGE.

Against WW2 AP projectiles the best armor BHR was 255 - 265 BHN, the level of the Tiger Ausf.E's armor, the same armor which managed to stop 76mm & 77mm Allied AP projectiles at point blank range! Yet the 88mm KwK43 L/71 is capable of punching holes in this armor beyond 4 km if the thickness is 100mm! The KwK43 would punch through 100mm of 300 + BHN armor past 4km for crying out loud! The 122mm D-25T can hardly punch through 100mm of VERTICAL 240 BHN armor at 3km, the 88mm KwK36 L/56 being just ~10mm behind it.

And like Delcyros explains De marre's theory DOES NOT WORK for these projectiles! It works for solid shot AP projectiles, NOT APCBC, esp. not when slope is applied! The theory is from 1870 Glen! Not 60 years later when the APCBC projectile was introduced!

Also for the last time, the 88mm KwK43's APCBC projectile was designated Pzgr.39/43, NOT Pzgr.39-1, the 88mm KwK36's APCBC projectile was designated Pzgr.39-1!

Its time you get this into your head Glen, cause its getting really straining having to repeat it!

I've shown you the picture in which the Pzgr.39-1 and Pzgr.39 share SAME penetration ability. Kwk43 can also fire Pzgr.39-1 shell.

In spite of what type the projectile is, penetration is NOT directly proportional to KE (per square). The Data has proved this.

Even the Tiger Ausf.E infact remained superior in combat to any Soviet tank till the end of the war.

JS2 late version(from 44 mid) is much superior to Tiger Ausf.E. Its 120mm/60 degree upper glacis amor is immune to any German tank gun and its 160mm turret front amor can only be penetrated by kwk43's APCR within 800 meters. That's to say, Tiger Ausf.E can NOT penetrate Js2 late front amor at point blank range in spite of what type shell used(APCBC, APCR). Lower glacis amor of any tank is easily to penetrate and seldom to hit, so ignore it.

Believe it or not.

[delcyros]

All things beeing equal, doubling the velocity will not quadrupel the penetration. It´s actually short of this, in between (roughly) ^1.4 and ^1.7, depending on the projectile in question (the projectile determines specific penetration).

Russian armour usually was very hard (400+ BHN) but typically of very low tensile strength and limited ductility with accompanied manufacturing related deficiancies. Laminations and bubbles were recorded very often in them. Basically, the russians were producing overhard cast plates, which were not as good as high quality plates of lower BHN levels but occassionally very tough and much easier to produce. They would have been superior if they would have been of entirely good quality with regards to tensile strength and ductility. But there was no technology existing to produce 100mm +, 400 BHN plates with these properties. These deficiancies make penetration tests very chancy for the soviets.

A high velocity, 75mm projectile, impacting an JS-II may not make it through but will throw off enough armour material from the backside of the RAS plate to deliver fatal damage inside on their way. These high velocity "discs" are a serious thread, typical for overhard plates. Another problem with overhard plates is that the projectile, if engaging the armour at high obliquity, may stretch the plate (and in this regard low tensile strength is negative) to it´s limits, if the projectile start enough sideway movement of the plate to "overstretch", the plate will shatter.
On the other hand, very high velocity projectiles impacting are moving close to the speed, where the filler explodes (if enough deceleration is induced). That´s why just giving more striking velocity will not always asset penetration. Then You will have to move to a larger (=heavier) projectile. The proposed 75mm L100 falls into this category.

[Juha]

Glen
I know, IMHO many of the photos were taken to show that it could be done and to show an extraordinally deed. In war one must try to cope with equipment at hand even if that meant rather suicidical tactics. IMHO with closely grouped multiple hits the penetration was possible to achieve a bit farer away. IIRC Soviet tactic was to open fire with all 4 guns of an AT battery against a single Tiger. Only after/if the first Tiger was neutralized the fire was shifted against another target.

Juha

[plan_D]

"JS2 late version(from 44 mid) is much superior to Tiger Ausf.E. Its 120mm/60 degree upper glacis amor is immune to any German tank gun and its 160mm turret front amor can only be penetrated by kwk43's APCR within 800 meters. That's to say, Tiger Ausf.E can NOT penetrate Js2 late front amor at point blank range in spite of what type shell used(APCBC, APCR). Lower glacis amor of any tank is easily to penetrate and seldom to hit, so ignore it.

Believe it or not."

I don't believe it. Read Soviet combat reports, the IS-2M was being knocked out by Panthers and Tigers at ranges up to and including 1,000 metres and it's D-25T could only penertrate the Panthers armour up to and including 600 metres.

The IS-2M suffered from poor armour quality and the crews suffered as a result. The Soviet industry considered tempering the IS-2M armour too expensive and time consuming so the problem remained until wars end. The numbers look good when studying the IS-2Ms armour, it was designed to be immune to the Tiger at ranges up to 1,000 yards - but it wasn't and that's a fact.