Suugestions for CMBB Combat: Panther Glacis Resistance and IS-2 Ammo Use

[rexford]

Miles Krogfus recently sent me some very valuable information on German weld and armor quality, as well as firing test data against Panthers from Aberdeen Proving Grounds (3 tanks) and Shoeburyness England (1 tank).

The firing tests were conducted against glacis armor which had not been previously hit, and the the tanks had not burned.

Miles' information shows that German alloy use for welding was cut starting January 1944. The firing tests show that glacis armor on 3 of 4 Panther tanks (Ausf A and G), when under attack by rounds which should not penetrate (17 pdr AP and APCBC, 90mm APCBC), developed cracks, sprung welds and allowed some complete penetrations that should not have occurred.

If the manufacture of Panther glacis armor and accompanying welds started to stand a statistical chance of lowered resistance during early 1944, this would include a good sized percentage of Panther A tanks.

From a wargaming perspective, CMBB scenario's from about June 1944 could allow the German player to pick Panther tanks, but the knowledge of how many could have deficient glacis armor and welds would not be known. The percentage might increase with the months that follow June 1944, if that month is selected as the "start date". Otherwise players who suspect Russian use of 100mm, 122mm and 152mm guns might opt for Panther D and early Panther A.

For Russian players, IS-2 tanks appear to have received and used AP or APBC in no particular set pattern, based on Russian Battlefield articles regarding IS-2 development and combat use. It could be a random selection whether the IS-2 fires AP or APBC, where APBC is much more effective against sloped armor.

So players might face two random selections, Panther glacis quality and 122mm ammo use. A similar ammo use randomizer would apply to 85, 100mm and 152mm rounds, which could be either AP or APBC. And the degree of Panther glacis resistance decrease could also be random.

I would also note, for the benefit of the CMBB design team, that the slope effects for AP rounds in the book, WW II BALLISTICS: Armor and Gunnery, have been revised after analysis of recently discovered firing test data for angles over 40 degrees.

When 122mm AP hits 85mm glacis armor at 55 degrees, the slope multiplier should be about 2.08. This is much lower than previously thought, and closely matches the reported penetration range of 122mm AP against good quality Panther glacis armor.

If someone from BTS will contact me directly I will e-mail them the new slope effect curves and the accompanying table as jpeg files. This information will also be e-mailed to others who might like the new curves (and table).

---------------------------------------------

Theories have been put forth by several persons on other sites that sprung welds may have been responsible for complete penetrations that should not have occurred against Panther glacis. That cracking a weld line would decrease the penetration resistance on follow-up hits.

Opinions on this issue would be appreciated.

[LGMB]

Soldier,

Blah blah blah, gamey, blah blah blah.

Sounds like some exstansive research, which I'm much to lazy to actually read. Hold on, I think I just heard Fionn...

[Mattias]

Is there any indication as to how well known these hidden traits of the armour and ammunition were to the troops?

Though I love the details myself I can never quite escape the feeling of being a gamey bean counter with rear view mirrors if I pick out the tanks that turned out to be the best in the game, as opposed to the ones considered the best during the war.

Personally I'd rather not know exactly how flawed my armour was, just add "armour flaws possible" to the list of special features of the vehicle and have chance (backed by facts) make the decision as to it's exact nature.

M.

[kipanderson]

Rexford, hi,

Very interesting stuff.

When it comes to the Soviet ammo one will no doubt be able to select the number of AP and APBC rounds one wishes for in the editor. As one can for western rounds in CMBO.

When it comes to the Panther some random chance of a low quality glacis would be realistic, and therefore deeded. Mind you, the Panther is already, in CMBO, assumed to have low quality armour.

I have just dug my copy of your ballistics book out of storage, and would be very grateful for the undated slope affects regarding AP ammo.

You can email me at

kipanderson@clara.co.uk

Thanks.

All the best,

Kip

[Priest]

Thanks Rexford, interesting as always!

Don't let these numbnuts stop you from posting, I learn something every time you do and that is not something I can say about a lot of things I read!

Thanks

[M Hofbauer]

I was under the impression that the IS-2 with it's 122mm had mostly HE in its ammo loadout, since -although it proved to work well in that regard - it was not meant to engage other tanks (apparently that was the job of the 85mm-equipped AFVs sich as the SU-85 and T-34/85) but to support of main assaults.

Considering the generally limited ammo storage of the IS-2, there won't be a lot of slots left for either AP *or* APBC if a historical ammo loadout will be modeled.

If those half a dozen rounds of AT ammo should be further split between AP and APBC I'm not sure.

If CMBB will model the IS-2 with an ahistoric, substantial amount of AP/APBC ammo, it will turn the vehicle into something it historically never was meant to be - a tank-hunting tank.

[ 01-19-2002: Message edited by: M Hofbauer ]</p>

[rexford]

The Russians spent alot of time and effort deciding which gun goes in the IS-1 and IS-2. The IS-1 with its 85mm was a failure, and the Russians noted that the 122mm gun was the most effective weapon at Kursk against Tigers and Panthers.

The 122mm gun was chosen for the IS-2 after firing tests against captured Panthers, and the Russians were quite upset during the Panther-vs-IS-2 combats when 122mm AP always bounced off the glacis beyond 700 meters, and usually ricocheted at all ranges.

The Russians were looking into improvements to the 122mm AP ammo when 122mm AP started to improve against Panther glacis during the summer of 1944 (due to more brittle glacis armor as a result of alloy rationing, according to Russian speculation on the subject).

The performance of 122mm AP against the Panther front was a major problem for the Russians for many months, which suggests that IS-2 tanks were expected to take on Panthers and defeat them with armor piercing rounds. If 1/3 of the 122mm ammo load is AP or APBC, that's about 10 rounds.

At 1.5 rounds per minute that equates to 6 or 7 minutes of continuous AP/APBC fire.

How many minutes of continuous APCBC fire can a Panther do? Say 6 rounds per minute for 7 minutes, 42 shots. That sounds like the Panther APCBC ammo load could be shot off in the same time frame that an IS-2 takes to shoot all the AP/APBC.

An SU 85 actually carries more HE than AP/APBC, we have seen the Russian figures. Most Russian tanks carry more HE than AP/APBC, from what we've seen.

SU 85, T34/85, KV 85 and IS-1 (85mm gun) were failures against Tiger and Panther, IS-2 was developed to take on Panthers and Tigers and blast the heck out of German bunkers and emplacements. 122mm HE was much more effective against structures than 85mm HE, where 85mm HE probably caused less fragmentation than 76.2mm HE.

IS-2 was developed to fight German "cats" and blow up emplacements and structures. Slow rate of fire and limited ammo load are the trade-off. But a limited ammo load is not as much of a problem as it would seem if the rate of fire is very low.

CMBB should keep the IS-2 ammo load and proportions historically correct, but IS-2 did fight German tanks and when the IS-2 did not do well in the first several months of fighting Panther the Russians were worried. That is one of the reasons why the IS-2 front hull armor was greatly improved, due to the heavy losses that IS-2 tanks suffered. A 75mm Pak did not kill IS-2 tanks frontally, Tigers, Panthers and Nashorn did.

[Andreas]

I am beginning to wonder whether this could not be handled a bit more mission specific?

I am just speculating here, but say you are about to assault some part of the German line in Poland in early 1945 with your IS-2 tanks. Battlefield intel suggests that no German armour is present. How do you stock out your tank for the mission? Sure, take a few rounds AP along just in case a pesky Stug shows up, but apart from that your job is to get in there, and get the Germans out there, which is best done by blasting them to Berlin with HE. Since you are constrained, you choose a lot of that, and little AP. In CMBB terms - leave it to Beaver, the scenario designer (now for the well-known refrain: 'who cares about QBs ).

I would be interested if anyone could tell me whether pre-battle procedures were that flexible or not. Maybe someone who has read Loza?

Regarding the length of battle - I just read an account by a Stug driver (Sturmgeschuetzbrigade 276), where nine Stugs took on five T-70 and a few T-34, knocking all of them out in a battle that lasted 50 mins. Sounds to me like they spent most of the time stalking, not shooting.

[Andreas]

<blockquote>quote:</font><hr>Originally posted by Andreas:

I would be interested if anyone could tell me whether pre-battle procedures were that flexible or not. Maybe someone who has read Loza?<hr></blockquote>

Anyone?

[Jeff Duquette]

<blockquote>quote:</font><hr>Lorrin Said: The Russians were looking into improvements to the 122mm AP ammo when 122mm AP started to improve against Panther glacis during the summer of 1944 (due to more brittle glacis armor as a result of alloy rationing, according to Russian speculation on the subject).<hr></blockquote>

Vasiliy on the Tankers forum has already indicated a very plausible explanation to the "decrease" in quality of the Panther's glacis to which you are alluding. I am curious why you choose to ignore this information?

<blockquote>quote:</font><hr>Vasiliy Said (brought from tankers forum) …with respect to disappearance of the problems with 122mm AP, but you are ignoring the fact that at the same time full-body Br-471 started being replaced with Br-471b, which would defeat the Panther's glacis regardless of its quality. How much influence did the appearance of new round have on disappearance of the problems?

Best regards,

Vasiliy

<hr></blockquote>

Again I personally do not doubt German armor quality declined as the war progressed, however the correlation you are attempting to draw between this sudden decline in Panther Glacis quality as a function of the Soviet D-25T's increased killing ability - post summer 1944 -- seems to ignore the introduction of improved ammunition on the part of the Soviets during this same time period.

<blockquote>quote:</font><hr>Lorrin Said: The Russians spent alot of time and effort deciding which gun goes in the IS-1 and IS-2. The IS-1 with its 85mm was a failure, and the Russians noted that the 122mm gun was the most effective weapon at Kursk against Tigers and Panthers.<hr></blockquote>

This is inconsistent with my references that indicate the D-25T was developed from the A-19 during a crash program by the Petrov artillery design team. The motivation for rapid adoption of the A-19 and the subsequent crash design program was apparently motivated chiefly by ammunition availability for the A-19 and thus the IS-2's D-25T. 122mm corps gun ammunition was already readily available in the Red Army's supply network (see Zaloga's "IS-2, Heavy Tank").

[rexford]

Jeff,

I answered Vasiliy's post on Yahoo!Tankers site. Didn't you read my response?

The Russian Battlefield site clearly differentiates between performance of 122mm AP and APBC (have you read the section?). For combat with Panther prior to summer 1944, Russian Battlefield says 122mm AP only penetrates glacis to 700m and mostly ricochets at all ranges. 122mm APBC penetrates to 1200m, so site indicates that AP and APBC available at same time and discusses each separately.

Russians started to look into ammo improvements due to poor performance of 122mm AP and then during summer 1944 AP effectiveness increased, so problem starts to disappear or at least become less critical before improvements found and implemented.

This is how I responded to Vasiliy's post.

I suspect that 122mm AP and APBC were both being made in about equal quantities due to the Russian worry about 122mm AP ineffectiveness (AP is cheaper than APBC and equally effective against Pz IV and StuG III, which make up a good percentage of IS tank opponents).

If you read the Russian Battlefield discussion you'll see that Russians weren't even aware of superior performance of 122mm APBC against thick sloped armor prior to first few months of IS-2 vs Panther combat. Then the Russians went to the designers and conducted firing tests to explain why APBC penetrated at greater ranges than AP.

There was no movement to replace 122mm AP with APBC due to sloped armor penetration differences prior to summer 1944 because the Russians were not aware of the differences. If you read the discussion on Valera's site most of your comments would be answered.

IS-2 was clearly expected to deal with Panthers and Tigers.

I never discussed why 100mm gun was not chosen for IS-2, and do not intend to. I spoke on why 85mm gun in various Russian AFV was not sufficient to fight Panthers and Tigers, which made 122mm gun in IS-2 a big need.

[Jeff Duquette]

Lorrin:

The RMZ article on the development of the JS-II which is seemingly the keystone reference to your degradation of German armor steel argument also indicates the following regarding the JS-2:

" In the beginning of 1944, an attempt was made to improve the protection of the JS-2 by tempering the front armour to very high hardness."

Tempering does not harden steel. Tempering toughens steel and results in decreased tendency toward cracking or spalling under impact loading. Tempering typically results in slightly reduced hardness as a trade off for increasing toughness.

[rexford]

Jeff,

The Russian Battlefield article is not the keystone to any argument, it is a piece that helps to put many other materials in perspective.

The Americans in Europe did tests during August 1944 that showed previously undamaged Panther plate to be brittle and crack in two of three cases after a few non-penetrating hits.

Firing tests conducted at Aberdeen Proving Grounds (3) and Shoeburyness (1) after August 1944 also show a tendency of some undamaged Panther glacis to crack on non-penetrating hits. The date of Panther manufacture in those cases is also consistent with the Russian reports.

The Russian reports suggest that summer 1944 is when the brittle results started to become noticeable. So Panthers in Russia and Italy prior to summer 1944 probably carried excellent armor to resist 122mm hits so well during the cold winter and early spring of 1944.

The Russian reports are being translated into English by non-metallurgists. Armor is heat treated to a higher hardness, which might have been translated as tempered.

The explanation about alloy shortages leading to Panther glacis problems seems to make sense but may not be strictly correct. Things like that happen during translations by non-metallurgists.

But when the Russian Battlefield reports state that 122mm AP performance improved dramatically during summer of 1944, that is a direct statement. The Russians connect the AP effectiveness change to Panther glacis problems related to alloy availability, which is consistent with many other materials and tests.

Lorrin

[M Hofbauer]

<blockquote>quote:</font><hr>Originally posted by rexford:

SU 85, T34/85, KV 85 and IS-1 (85mm gun) were failures against Tiger and Panther, IS-2 was developed to take on Panthers and Tigers and blast the heck out of German bunkers and emplacements. 122mm HE was much more effective against structures than 85mm HE, where 85mm HE probably caused less fragmentation than 76.2mm HE.

IS-2 was developed to fight German "cats" and blow up emplacements and structures. Slow rate of fire and limited ammo load are the trade-off. But a limited ammo load is not as much of a problem as it would seem if the rate of fire is very low.<hr></blockquote>

I do not argue with the fact that the IS-2 turned out to perform well against german tanks, but my point remains that that was not its intended main employment.

to quote from Valera's excellent site which has repeatedly been cited in this thread:

(when comparing the IS-2 and it's AP performance with the Panther) Today, most tank enthusiasts are interested in the AP ability of tank guns, forgetting the HE ability. However, that is ridiculous and stupid! The IS-2 was a heavy breakthrough tank, i.e. a tank intended for breaking through the enemy's lines of defense. In other words, the main targets of this tank were infantry and artillery. Thus, a tank with a large gun with great HE capability was needed. History showed that the IS-2 used about 70% of its HE ammunition and only 30% of its AP ammunition.

That's why the HE ability was considered more important.

It is even more important when you consider that with..what, er, 28 rounds ...and most of it being HE then there isn't much left for AP *or* APBC. Which was my priginal point.

[PJungnitsch]

From what I've read the Stalin was upgunned specifically because it was viewed as inferior with the 85mm against the heavy German tanks. Infantry and artillery were not the driving concern. Again, from Russian Battlefield:

<blockquote>quote:</font><hr>The first person to suggest arming the JS tank with a gun larger than 85 mm was the Director and Chief Designer of Factory #100, Zh.Y.Kotin. He realized in August 1943, after studying the results of the Kursk battle, that the most effective anti-tank weapon employed against German Tigers was the Corps 122 mm Field Cannon A-19 Model 1931<hr></blockquote>

and:

<blockquote>quote:</font><hr>In regards to fighting the Panther tanks the tests at Kubinka clearly show that the 122 mm D-25 gun (V=780-790 m/s; g=25 kg) is superior to the 100 mm D-10 gun (V=890-900 m/s, g=15.6 kg).<hr></blockquote>

[ 01-21-2002: Message edited by: Paul Jungnitsch ]</p>

[Grisha]

Interesting thread. I was under the impression that all Soviet tanks were primarily vehicles meant to engage infantry positions and emplacements. Certainly, the IS-2 was a response to the Tigers and Panthers, but antitank was a secondary function for it. Even the T-34 was designed within operational specifications rather than tactical concerns. It just so happens that the T-34 was better than anything else in 1941.

As for the IS-2 main gun, I was also under the impression that overall the 100mm cannon was a better weapon than the 122mm when it came to a purely antitank role. The 122mm was chosen because it could fulfill both the antitank and antipersonnel role within acceptable specifications.

[Commissar]

<blockquote>quote:</font><hr>Originally posted by Grisha:

Interesting thread. I was under the impression that all Soviet tanks were primarily vehicles meant to engage infantry positions and emplacements. Certainly, the IS-2 was a response to the Tigers and Panthers, but antitank was a secondary function for it. Even the T-34 was designed within operational specifications rather than tactical concerns. It just so happens that the T-34 was better than anything else in 1941.

As for the IS-2 main gun, I was also under the impression that overall the 100mm cannon was a better weapon than the 122mm when it came to a purely antitank role. The 122mm was chosen because it could fulfill both the antitank and antipersonnel role within acceptable specifications.<hr></blockquote>

I believe that another reason why the 122m was chosen for the IS-2's main gun was the shortage of 100mm guns and ammo. 122mm guns were already quite plentiful and available.

[PJungnitsch]

<blockquote>quote:</font><hr>Analyzing the results of those (note these battles were tank vs tank) battles, the GBTU came to the conclusion that the armament and protection of the JS-1 didn't correspond to its intended tasks and was inferior to the German heavy tanks. GBTU recommended increased armor protection and rearming the JS-1 with a more powerful weapon<hr></blockquote>

Again, no mention of rearming the Stalin because it was needed to take out infantry better...

[ 01-22-2002: Message edited by: Paul Jungnitsch ]</p>

[PJungnitsch]

Similar reasons for upgunning the T34, as far as I can see, not anti infantry and artillery, but anti tank:

<blockquote>quote:</font><hr>In his introduction, V.A.Malyshev noted that the victory at the Battle of Kursk cost the Red Army a high price:

"Enemy tanks opened fire on ours at distances of up to 1,500 metres, while our 76 mm tank guns could destroy "Tigers" and "Panthers" at distances of only 500-600 metres. Imagine the enemy has a kilometer and a half in his hands, while we have only half a kilometer. A more powerful gun needs to be put into the T-34 quickly."

In actual fact, the situation was significantly worse than Malyshev painted it, though attempts to correct the situation had been undertaken at the beginning of 1943.<hr></blockquote>

[Jeff Duquette]

<blockquote>quote:</font><hr>Lorrin Said: The Americans in Europe did tests during August 1944 that showed previously undamaged Panther plate to be brittle and crack in two of three cases after a few non-penetrating hits.<hr></blockquote>

Lorrin:

It is still unclear to me how you are arriving at the conclusion that the three Panthers subjected to firing trials at Isigny in Aug 1944 were all in an undamaged condition prior to conducting the trials. I have the entire text of the report and there is no verbiage that elaborates upon the condition of the three Panthers at the time of their capture. I can only assume that you are confusing the July 10, 1944 Balleroy report with the Aug 30, 1944 Isigny test report. Some form of firing trial dyslexia? The Balleroy firing trials report actually does contain a snippet indicating:

<blockquote>quote:</font><hr> REPORT OF PROCEEDINGS OF BOARD OF OFFICERS

Organization: Headquarters, First U.S. Army.

Place: APO 230, U.S. Army.

1a. Firing was conducted on terrain permitting 1500 yards maximum range with zero angle of site. All guns and types of ammunition, suitable for anti-tank purposes, available to First U.S. Army were defeated on targets whose armour plate was slightly burned. Upon determination of critical ranges , all penetrations were proven against the armor plate of a German Mk V "Panther" Tank with armor undamaged and in excellent condition. All firing was conducted normal(2) to the target. No firing was conducted against the German Mk VI "Tiger" Tank as there were none available.<hr></blockquote>

Is the quote above what you keep referring to?

I would be more than happy to forward to you a complete copy of the Balleroy and Isigny Reports...in exchange for complete copies of the Shoeburyness and Aberdeen firing trial reports for the Panther . Has Miles K. given you the actual firing trial reference information for the Aberdeen and Shoeburyness Reports...Or is that still a military secreat? The Shoeburyness firing trial report for the Panther is not amongst the numerous firing trial reports at the PRO. Perhaps Bovington archives has the document?

[ 01-23-2002: Message edited by: Jeff Duquette ]</p>

[TSword]

Rexford, as always, your posts are a delight to read, some light in the dark...

Question: Is the slopemultiplier above 40° the same for all t/d ratios ? (t = thickness of plate, d = diameter of round)