IS-2 Tank Role and Gun Selection

[Jeff Duquette]

Lorrin Said If one goes to the following page on Russian Battlefield, and reads the three correspondence letter on IS tank use of 100mm gun, they will see interesting reasons why 100mm gun not chosen for IS tanks:

100mm gun out penetrated 122mm at normal combat ranges but came with many drawbacks, including longer rounds to load into gun, increased fumes in turret, insignificant increase in ammo storage, etc. See letter 3.

More than penetration went into decision to stick with 122mm, which may have also considered HE capability. 122mm HE projectile is 15.2% HE filler by weight, 100mm HE is 9.3%, based on figures contained on Russian Battlefield.

The adoption of the D-25T to the IS-2 appears to have been ultimately a case of simple wartime expedience. Ammunition and the facilities to produce ammunition were readily available for the A-19/D-25T.

From: Zaloga & Sarson's "IS-2 Heavy Tank, 1944 - 1973"

The obvious solution was to mount a long-barreled 85mm gun or 100mm gun which offered the anti-tank performance of the D-25T, but which would permit a larger ammunition load. The original IS-1 carried double the ammunition load of the IS-2, 59 rounds against 28, due to the smaller volume of the 85mm ammunition. The 85mm gun was reconsidered on the izd-244 prototype, using the improved S-53 gun. However, the anti-armour performance of this weapon was not adequate. The izd-245 and izd-248 were fitted with new 100mm guns. Although the ballistic performance of the new D-10 100mm gun was superior to the 122mm D-25T in the anti-armour role, the problem still remained that there was a surplus of 122mm gun tubes and 122mm ammunition production capacity, and an inadequate supply for the 100mm gun alternative. This approach was therefore rejected in spite of its technical merits.

Lorrin Said U.S. firing tests with 122mm APBC predict that 122mm APBC will defeat excellent quality Panther glacis at 1450m against 85mm plate thickness, and 1850m against 80mm plate thickness.

Zaloga also indicates that based upon combat experience the Panther needed to engage IS-2 frontally at combat ranges of 600 meters or less to insure a decent chance of success. Conversely the IS-2 had to close to 1000m or less to insure a decent chance of success. Seems inconsistent with the 1972 AMMRC penetrations stats for the BR-471B. I think you will be hard pressed to find more than a handful (if that) of useful AAR's detailing actual tank vs. tank engagements of IS-2 vs. Panther. So much of what you have been suggesting appears to be speculation at this point.

[Charlie Rock]

A few thoughts:

I have also seen a copy of the javelin hit. A hollow charge warhead like the jav would probably blow a hole through the roof, and probably the floor as well.

In the Gulf War, it was common to see pictures of T-72s with the turret blown off the tank and lying upside down nearby. The reloading mechinism for a T72 is exposed and not compartmentalized, like an M1. A sympathetic explosion would result if a round penetrated, and set off the T-72's main gun ammunition. I believe it was approxiately 30 rounds. If I am off, I admit defeat to a counter-grog argument.

Anyway, in that explosion the turret is blown completely to bits. I would venture that rather than main gun round propellent, it was packed with C4, with some fuel to make the nice mod-like flash and thick black smoke.

As to the engine controversy from the panther:

I don't believe an AP round would do that. Why, for example, did the round not penetrate the engine, rather than blow the engine out? Should we assume it penetrated the front armor of the tank, but when striking the engine block did not penetrate the block but sheared every hose and pipe and pushed the whole engine out the back, through the rear armor?

I have seen an engine do that however. In this case, an antitank mine blew up under the front of an M113 (It was a range test). The entire engine was blown bodily out the back, through the rear door, and 20 feet beyond. The M113 was either blown on it's side or back, I don't remember which.

I would postulate that if the shell hit the equivalent, say 20-30 lbs of explosives, such as high explosive shells stacked in the back of the turret, that may have vectored an explosive force that blew the engine out. A single shell probably wouldn't do it.

Jason, according to your math, if this engine was going 4 or 12 mph, in the time it took it to drop to earth from a height of 5 feet in the air, it would probably go, horizontally, a couple of feet.

Based on my observations, 20+ lbs of C4 will blow an engine 20-30 feet, after knocking the back ramp off it's hinges.

I was surprised as heck to see that engine lying in the dirt; it can be done. My money is on a secondary explosion.

[ February 11, 2002, 12:00 AM: Message edited by: Charlie Rock ]

[JasonC]

It may well have been a secondary explosion in the particular case. But the big AP rounds have more energy than people's native intuition seems to credit them with. From the 88L71 upward, over 5 million joules, things start to happen that your intuition would not credit if based only on less energetic rounds, like medium velocity 75mm and the like. And here is nothing incredible in e.g. modern HV AP rounds doing things like lifting turrets. Look at what is necessary in recoil system design on the firing end to deal with the energy that throws the round in the first place. But whatever, I've said my piece on the subject so I'll give it a rest.

[Roksovkiy]

The Panther - kubinka story has been adapted and changed in various books since the event. The only fact that remains is K.E.Voroshilov nearly having is head blown of with the muzzlebrake accident.

From Red Steel "IS-2 development"

"The JS-122 (Object #240) passed the Government tests quickly and successfully. Thereafter, the tank was moved to one of the Moscow military testing grounds where it was demonstrated to K.E.Voroshilov.

The tank's 122 mm gun was fired from 1500 metres at a captured German Panther tank.

The round hit the SIDE of the Panther's TURRET, penetrating it cleanly and tearing the opposite side out at the welded seams, throwing it back a few metres. During these tests the muzzle brake of the A-19 blew up almost killing Voroshilov. After this accident it was decided to change the muzzle brake to a 2-chamber design similar

to that used by the Germans."

It’s amusing how events change over the years to glorify what happened. The front glacis-engine out the back, makes a much better story that the measly 40mm side turret.

[MajorBooBoo]

I have read of panther turret sides opening up/falling off on occasion. If you have ever stood next to a panther, and seen how large it is and vulnerable to the sides, perhaps it would not be your choice of tank.

I can believe that an AP would penetrate through and perhaps knock off the back plate of the hull (But not take the engine along!). the reason being that the welds are to strengthen outside attack. That overlapping german welding interlock does not help an inside attack. Also gravity might help drop that plate like a ramp! But I havent seen a pic like this of a panther.

To get back to the main point of this thread, The IS2s (to me) should be used in combo with terrific arty/rocket/sturmovic and assault guns to crash a selected area of the german line. The HE rounds being spent taking out bunkers and other stubborn points of resistance. After the main breakthrough, these tanks could help hold the breakthroughs flanks with the AP they carry to stop german armor counterattacks.

I wouldnt use them as offensive weapons against german armor.The rates of fire and inabilty to unload and switch ammo type (they probably cleared the barrel by firing) makes them ponderous.

[rexford]

As I noted to Jeff on the Tankers site, the ranges quoted by Zaloga for Panther vs IS-2 combat appear to take into account accuracy as well as penetration. Zaloga's quotes do not state ranges were limits of expected penetration, they state that those were the ranges for effective combat (which I interpret as hit and kill combination).

Russian Battlefield includes statement that IS-2 crews would be hard pressed to hit beyond 1000m unless very well trained and experienced. During first months of IS-2 use few crews would qualify as experienced. Does Zaloga indicate what period of the war his quoted penetration ranges refer to.

With regard to the use of U.S. 122mm APBC firing tests to predict penetration of WW II IS-2 against Panther front, Jeff ignores the many excellent predictions that we have made using the U.S. test data.

100mm APBC against Panther glacis is predicted to within 100m or so in our book (which Jeff has). A post that analyzed Russian firing test data for 85mm APBC against Pershing armor is on Tankers site where penetration ranges against 101mm cast at 43 degrees, and other areas. is very closely predicted when compared to Russian test findings.

For 100mm and 85mm APBC we predicted results from 122mm APBC firing test data from U.S., modified for slope effect and impact velocity.

The number of test firing results that support use of U.S. firing test data for 122mm APBC, and predictions for other Russian APBC from that data, continues to increase each month. Instead of being hard pressed to find reports and tests to support our findings and predictions, the data base is increasing at a steady rate.

Regarding that 11/43 test of 122mm against Panther glacis, Miles Krogfus has the original test report and it states the following:

Tank was knocked out during July 1943 by a 76.2mm side hit. Was brought to Moscow for show, insides were stripped out and the tank was subjected to firing tests (engine is removed at this point along with other internal mechanisms in hull and turret).

122mm hit on glacis goes through and then exits through 40mm rear hull plate.

The story about a 122mm round penetrating the turret side and going out the other side may have also occurred during 11/43 tests, but Miles is concentrating on the glacis/hull rear report aspects.

Claus Bonnesen used the serial number for the Kubinka tank that Miles presented on Tankers site to identify the Panther tank number. Picture of that tank on Russian Battlefield site show it to be in good condition after Russian capture, prior to Kubinka tests.

U.S. firing test data with 122mm APBC predicts 1800m+ penetration of 80mm at 55 degrees, 11/43 test shows penetration range is way more than 1500m if round defeats glacis and rear hull.

Russian firing test at Kubinka during 9/44 shows 122mm penetrating Panther glacis at 2500m.

Lorrin

[rexford]

In response to the 122mm goes in and out Panther (in glacis and out the rear hull), a post on the Tankers site noted that a Sherman vet made a scale model diorama where a Sherman was sitting with a hole in the glacis and the engine sitting well beyond the back of the tank.

Turns out the diorama was not depicting maintenance, the situation was directly after a 75mm or 88mm German round penetrated the glacis and drove the engine off the mountings and out the tank rear.

The post concluded that strange and unusual things do occur, like a 37mm armed armored car knocking out a Panther on a frontal shot (actually happened).

Lorrin

[rexford]

In response to an earlier post on this thread regarding differences in penetration ranges for 122mm ammo against Panther glacis, here is an explanation:

122mm APBC has a flat nose and superior performance against sloped armor, since ricochet causing forces are decreased with a flat nose.

U.S. firing test data for 122mm APBC at angles from 0 through 70 degrees predicts 1800m+ penetration range against 80mm @ 55 degrees Panther glacis.

11/43, 122mm goes thru glacis and out hull rear at 1500m, which suggests penetration range above 1500m

9/44, 122mm goes thru glacis at 2500m with energy to spare, we interpret this result as due to flawed or brittle armor which decreased penetration resistance

Zaloga indicates 1000m or less range to effectively fight Panthers, well, hitting beyond that range may have been a problem which would be magnified due to 9 or 10 rounds of armor piercing ammo (can't afford to sit back at 2000m and fire away hoping for a hit). One important factor is the time frame that the Zaloga quote comes, since early IS-2 crews might have alot more trouble hitting beyond 1000m than late 1945 crews which fought duels with Tiger tanks at 2500m and beyond.

Russian Battlefield states that APBC could penetrate Panther at 1000m and 1200m, well, maybe accuracy, ammo limits, terrain and other factors limited hits to those ranges.

Regarding Russian AP, Russian Battlefield gives it a 600 to 700 meter penetration range against Panther glacis till summer of 1944, when armor appears to lose resistance and effective range increases.

If the IS-2 tanks that Zaloga's quote applies to were carrying mostly AP, then the effective range to fight Panthers frontally would be 1000m at some point.

Lorrin

[JasonC]

Rexford, I am interested in the 37mm vs. Panther front claim, because I have tried to track down and verify a number of 37mm AP claims in the past. Usually I have found something wrong with them, and I wonder if extreme claims for US 37mm AP are something of an ongoing urban legend.

I tracked several US 37mm vs. Tiger I claims and they failed to pan out, for discernable reasons. Like no Tigers in the area at the time of the alleged incident, etc. I concluded that claimed rear penetrations of Tiger Is probably stemmed from rear penetrations of mis-IDed Panthers or Pz IVs.

I certainly don't know for sure about the Panther front claim, because among other things I don't know the occasion the other post was supposed to be about. But "actually happened", about a post by someone else on another sight, is not very convincing on its own, particularly on this subject.

In itself it is not terribly plausible, given the known regular defeat of US 37mm by typical DAK vehicles from the front, beyond about 500-750 yards. Which had at best 30mm+30mm layered plate, nearly vertical. Side or rear kills of Panthers would of course be plausible.

If possible, might you find out the unit involved, date and location, and any after-action-report from which the claim stems? Or alternately, ask the initial poster on the other site to email me that sort of info? If I can find anything to confirm or deny the tale, I'll report back here.

[rexford]

Jeff Duquette stated:

"The adoption of the D-25T to the IS-2 appears to have been ultimately a case of simple wartime expedience. Ammunition and the facilities to produce ammunition were readily available for the A-19/D-25T."

The discussion of whether the 122mm or 100mm should be on the IS-2, which is presented on Russian Battlefield, appears to have taken place during August 1944, well after IS-2 with 122mm was in production and use.

The discussion appears to be centered on whether the 100mm gun would be a better choice for future IS-2 tanks. The factors presented weigh against the 100mm gun.

The ammo availability factor was to later delay introduction of SU 100, based on Russian Battlefield articles, when 100mm APBC could not be produced in satisfactory manner.

The letters presented on Russian Battlefield appear to be based on experience with 100mm pre-production prototype. Ammo availability does not appear to be discussed in the three letters as a major factor.

[JasonC]

Rexford, thanks for the detail on the various tests. I don't find the back plate penetration at all surprising. But I am interested in the little puzzle you are examining.

My first guess is that the low ranges given on the Russian site refer to the difficulty of getting hits, rather than of KOing if a hit was achieved. But there is another possibility. It might be a change in the gun, more or less corresponding in time to a change in the average armor quality of the Panthers, as well.

The Russians have more than one 122mm. There is the short barrelled 122mm used in the SU-122, which was based on the ordinary field howitzer. I believe that was the M-30 model (some sources say "M-38", but I think it was the M-30 model from the year 1938). It had disappointing AP performance due to low muzzle velocity, so they used HEAT instead. But there was also more than one model of long, high velocity 122mm.

The first ISU-122s, for certain, and some sources I've seen say also the original IS-2s, used the 122mm model A-19. The later ISU-122s, from late '44 on, used the more powerful 122mm model D-25. And I've seen one source that says the IS-2s switched to the D-25 model, which the tank is usually listed as carrying, only with the IS-2m, in the spring of '44.

There may also be confusion between the D-25S, and the D-25T, but I have not seen anything to suggest the difference between those was substantial. The difference between the A-19 and the D-25 was substantial. The D-25 incorporated a larger muzzle break and overall improved recoil handling, which should have allowed larger charges and higher muzzle velocity.

So perhaps one set of results are 122mm A-19 against relatively high quality Panthers, and the later ones are the more powerful 122mm D-25 against lower quality Panthers. That might make a substantial difference. And if that is the case, it would certainly be worth knowing, and modeling for CMBB.

I hope this helps. Definitely your area of expertise...

[PJungnitsch]

The selection of AP vs APBC may have had something to do with the amounts of Tigers I's faced vs Panthers. As the amounts of Tiger I's dropped and Panthers and Tiger II's increased, it would have made more sense to stick with APBC.

Some quotes from 'Tiger vs Stalin' Notes for Panzer Troops:

1. Most Stalin tanks will withdraw on encountering Tigers without attempting to engage in a fire-fight.

Soviet recognition that the Stalin was not optimum for taking on the German heavies? Best to fall back and bring up a SU-100?

Stalin tanks generally only open fire at ranges over 2,200 yards and then only if standing oblique to the target

Oblique to target takes advantage of the heavy side armour, much like Tiger I's were trained to do. Still they sound convinced that the Tiger will hit first and are trying to minimize the chance, and the damage afterward. What was the loss rate of Stalins?

Enemy tanks crew tend to abandon tanks as soon as hit

Recognition that once the Tiger 'has the range' its best to get out of Dodge? Or emphasis from armour fragments flying through the crew compartment from the tempering problems?

The other points are very cautionary for Tiger crews, including:

Stalin tanks should not be engaged by Tigers in less than troop strength. To use single Tigers is to invite their destruction.

Translation 'This ain't no T-34.'

[dalem]

Originally posted by JasonC:

Rexford, I am interested in the 37mm vs. Panther front claim, because I have tried to track down and verify a number of 37mm AP claims in the past. Usually I have found something wrong with them, and I wonder if extreme claims for US 37mm AP are something of an ongoing urban legend.

I tracked several US 37mm vs. Tiger I claims and they failed to pan out, for discernable reasons. Like no Tigers in the area at the time of the alleged incident, etc. I concluded that claimed rear penetrations of Tiger Is probably stemmed from rear penetrations of mis-IDed Panthers or Pz IVs.

I certainly don't know for sure about the Panther front claim, because among other things I don't know the occasion the other post was supposed to be about. But "actually happened", about a post by someone else on another sight, is not very convincing on its own, particularly on this subject.

In itself it is not terribly plausible, given the known regular defeat of US 37mm by typical DAK vehicles from the front, beyond about 500-750 yards. Which had at best 30mm+30mm layered plate, nearly vertical. Side or rear kills of Panthers would of course be plausible.

If possible, might you find out the unit involved, date and location, and any after-action-report from which the claim stems? Or alternately, ask the initial poster on the other site to email me that sort of info? If I can find anything to confirm or deny the tale, I'll report back here.

Jason-

I have MacDonald's "A Time for Trumpets: the Untold Story of the Battle of the Bulge" in front of me. In a chapter relating 10th Armored's defense of Bastogne, a brief mention of a 37mm vs. Panther kill is made. Describing the actions of Team Desobry defending the village of Noville on the morning of 12/19/44. Pp 491: "With a 37mm. gun, an armored car scored a hit at some vulnerable point on a Panther and knocked it out; the gunner himself found it hard to believe." That's all I could find in there. I could swear I've read a more detailed account of that kill and the gunner actually checking out the wreck, but it's not in that book and I can't imagine what other of my sources it may or may not be in.

-dale

[Jeff Duquette]

Lorrin Said: As I noted to Jeff on the Tankers site, the ranges quoted by Zaloga for Panther vs IS-2 combat appear to take into account accuracy as well as penetration. Zaloga's quotes do not state ranges were limits of expected penetration, they state that those were the ranges for effective combat (which I interpret as hit and kill combination).

Lorrin:

Again I would suggest reading the passage in question (Pages 12 - 13, S. Zaloga & P. Sarson's "IS-2, Heavy Tank, 1944 - 1973"). It is obvious you have not looked at Zaloga's work, or you wouldn't persist with this insistence that Zaloga is talking about accuracy. He does in fact say "penetration" in all cases…not accuracy restraints, nor crew training problems, nor optics or gunnery constraints. You are in fact inferring a large amount of information into a passage that you have obviously not even read. I have already indicated as much on the Tankers Forum. Since it is apparent you do not own Zaloga's booklet on the JS-II, might I suggest you either open up your wallet and buy the thing, or once again try scrounging the information from Robert Livingston or Miles K..

[JasonC]

To dalem - I don't see anything in that account claiming the hit was from the front, just that a Panther was KOed by a 37mm. I know perfectly well that Panthers were sometimes KOed by 37mm. Panthers only have 40mm of armor, without appeciable slope, on their sides and rear, so this is not exactly surprising. The surprise of the gun crew apparently stems from such a small and old weapon sufficing to KO a 45 tons tank. But this doesn't mean it KOed said tank through the front aspect.

I've never seen a confirmed 37mm AP kill of a Tiger I, or of a Panther through the front. I have heard claim after claim after claim that both were done, but never one that panned out. My suggestion is to treat every extreme claim about 37mm AP effectiveness with extreme skepticism, and to be sure -

(1) the target tank is correctly IDed, preferably by photo of the wreck or at least accounts of its inspection after combat by someone who gives evidence of correcting IDing German tank types, and cross checked with other historical records to ensure such a type could be present

(2) that the aspect hit is clearly specified, preferably with a "thick description", as in "the round penetrated the left hull side below the track, just between the second and third return rollers" or what not

(3) the source of the 37mm is accurately IDed, as Greyhound, Stuart, towed 37mm, with the unit designation of a formation, date and place of the engagement, confirming that such a unit was present and was so equipped

(4) a staff history or oral AAR that recounts the overall fight in which the engagement occurred, clearly specifies the presence of German tanks, preferably including their model, and relates at least that losses consistent with the story occurred.

I have yet to see one that passes those scholarly tests. I've seen "M-8s" that were evidentally M8HMCs with 75mm HEAT, I've seen vehicles claimed to be in units that did not possess them, both on the US shooter side and the German shootee side, I've seen Tiger I claims in sectors of the front where there wasn't a Tiger of any kind within 150 miles on the day of the alleged engagement, I've seen Pz IVs called Tigers, Panthers called Tigers, accounts that specify dead Panthers but not front aspect turned into the more extreme claim, cases where cavalry units entered sectors where the operational history records tank engagements just prior to their arrival, and I have not seen, but suspect, some claims based on 1.5" holes in wrecks that might easily be due to bazookas.

From the ordinary ballistics data, one would expect that US 37mm could penetrate roughly 60-65mm of vertical armor. That is sufficient to KO any German tank from *some* aspect, except Tigers (I and II, and Jagd). It is sufficient to KO Pz IV and below from the front, if the range is short enough and the right part of the front is hit. Thus the only exceptional claims, worth investigation, are (1) 37mm vs. Tiger stories, where the default likely explanation is mis-ID of the target, and (2) 37mm vs. front aspect of Panther or TDs, where the default likely explanation is an incorrect report of the aspect of engagement.

Until I see a case that clearly passes all the above tests, I will continue to regard the extreme 37mm AP claims as pure urban legend. Notice that such urban legends have many motives, both in WW II history and in later times, among grogs in particular. It wasn't the gun it was how close you got it or getting behind them; cavalry boosting; excusing the continued use of Stuarts; general "they ain't so tough" propaganda; explanation of wrecks after the fact in certain sectors - among others from early on. And later, why unit XYZ in game ABC can add combat factors to KO this of that, with much more abstract, less accurate AT modeling than anything in CM - among grogs, simply justifying outcomes induced by rough game models. There are lots of reasons for the stories to circulate, independent of their truth. So poke them before you buy into them.

[dalem]

Originally posted by JasonC:

To dalem - I don't see anything in that account claiming the hit was from the front, just that a Panther was KOed by a 37mm. I know perfectly well that Panthers were sometimes KOed by 37mm. Panthers only have 40mm of armor, without appeciable slope, on their sides and rear, so this is not exactly surprising. The surprise of the gun crew apparently stems from such a small and old weapon sufficing to KO a 45 tons tank. But this doesn't mean it KOed said tank through the front aspect.

Right. My surprise when I reread that passage was that I have it in my head that I *did* read a similar account the *did* confirm 37mm kill specifically on a Panther front. I cannot back that up though. Even if true, I would have to believe it would fall under a "one in a million" vision slit/ball mount/patched section or something. But I gave you what I had.

-dale