Saturday 29 April 2017

E-50 and E-75: A Story of Failed Unification

Tanks that could have been built are often discussed within certain circles. Aside from the superheavy Maus and E-100, there are the light and medium E-10 and E-25 tank destroyers. Despite very incomplete data about these vehicles, the overall characteristics are known, including the armament.

Meanwhile, the core of "Panzerwaffe-46" was going to be composed of the medium E-50 tank and heavy E-75 tank, at least in the minds of fans of alternative history. The story with these tanks is a lot more complicated, since work stopped at an early stage, and a good half of the information available on these tanks is divination at best. Let's try to figure out what about the E-50 and E-75 is true and what is blatant misrepresentation.

Aim for Unification

The 6th Department of the Armament Directorate, and Heinrich Kniepkamp personally, tried to design a single platform for two types of tanks since the second half of the 1930s. This was caused by the strange situation where the Grosstraktor and Leichttraktor projects let to the appearance of the B.W. support tank and Z.W. medium tank. Even though the tanks were built for different purposes, their characteristics were very similar.

In early 1937, a reasonable idea of leaving just one of the two similar chassis in mass production came up. The Z.W.38 tank, which Kniepkamp participated in designing, seemed the most promising. This tank, unlike the preceding PzIII Ausf. B-D, was going to have a torsion bar suspension, which was successfully perfected on the Swedish Landsverk L-60 tank.

In Knipkamp's mind, the support tank would be built by putting a B.W. (PzIV) turret on top of a 4.Serie/Z.W. tank. In June of 1937, the military informed Krupp that the 2.Serie/B.W. (PzIV Ausf. B) will be the last batch of PzIV tanks. However, plans and reality rarely coincide. Work on the PzIV dragged on, and the first tank only entered trials in the spring of 1938. As a result, Erich Wolfert, Krupp's lead engineer, managed to keep the PzIV in production. The idea of building the military's main tank and a support tank on one chassis, like the British did with the Medium Tanks Mk.I and Mk.II failed.

Panther II, the first attempt to unify medium and heavy tanks.

The next attempt to create a universal tank platform was made five years later. In April of 1942, Henschel began working on the VK 45.02 (H) tank, also known as the Tiger II. During development, a decision was made to share components with the VK 30.02 (MAN) medium tank. In November of 1942, the VK 45.02 (H) turned into the VK 45.03 (H), which is also know as the Tiger III.

On February 17th, 1943, the minister of armament and ammunition Alber Speer approved the unification of the VK 45.03 (H) and the prospective Panther II tank. This time, the idea was not to build the tanks on one chassis, like with the B.W. and Z.W. The heavy tank would use a suspension with nine pairs of road wheels, the medium tank would use seven pairs. The Tiger III had a longer hull. The engine, transmission, cooling system, and road wheels would be the same.

Meanwhile, the Panther II was delayed, and the VK 45.03 (H) turned back into the VK 45.02 (H). It had nothing to do with the tank that was previously developed under that index. Finally, the VK 45.02 (H) was accepted into service as the Pz. Kpfw. Tiger Ausf. B. As for the Panther II, the project did not progress past a test chassis. The reason for this was that MAN was too busy producing the regular Panther. The decision to use the hull of this tank for the Jagdpanther tank destroyer also played a role.

In May of 1942, Kniepkamp started thinking about a new universal tank chassis. Unlike the Tiger III/Panther II, his idea was closer to what he did five years beforehand. Instead of unifying the parts, the heavy and medium tank would share a chassis. While the Tiger III/Panther II were still in development, this idea was not taken seriously. Nobody was going to work on an even more controversial project in parallel. Kniepkamp had to wait until the spring of 1943 when it became clear that the unification of the Tiger III and Panther II was going nowhere.

Without torsion bars or front transmission

A curious series of events preceded the work on a unified chassis. As we know, the VK 45.02 (H) and VK 45.03 (H) were not the only projects for a new generation of German heavy tank. In early 1942, Porsche K.G. began working on a heavy tank that was indexed Typ 180 or VK 45.02 (P) in March. Like the Henschel competitor, the armour of this tank was sloped.

As for the technical "filling", Porsche was true to himself. Porsche's designers did not share Kniepkamp's love of a front transmission, gasoline engine, or torsion bar suspension. The elements of the Typ 180's suspension, just like its predecessors, were moved out of the hull, and the drive sprocket was in the rear. Porsche's tank had serious issues with the engine. Air cooled diesel engines never reached an acceptable state. The military was also suspicious of the electric transmission. As a result, the Typ 180 was never even built as a prototype, and the turret that was designed by Krupp for this tank was "inherited" by the first 50 Tiger B tanks.

The E-50's chassis. Given a mass limit of 50 tons, only 10 remained for the turret.

It would seem that Kniepkamp's concept won. The Panther and Tiger B were both built according to the traditional German concept, which dated its way back to the interbellum Carden-Loyd tractor. However, the E series program launched by Kniepkamp in April of 1943 (Entwicklung, "development") departed from this concept.

Aside from the air cooled engine and electric transmission, it would appear that the 6th Department's chief developer copied his competitor's ideas. The E series had external suspensions and any kind of spring elements aside from torsion bars. Another feature of the E series was a rear transmission. The only prospective tank that would have had a front transmission was the superheavy E-100, but that had an obvious reason. The E-100 was a reincarnation of the earlier Tiger-Maus project, which had a spring suspension.

Two variants of the E-75. The Adler version was deemed more promising.

There were several reasons for moving the transmission back. The Carden-Loyd layout became complicated to service at a certain point. One can only imagine the headache that German repairmen got when a Tiger's gearbox in the middle of a field. In order to extract it from the tank, one had to take out a good half of its internals. Considering how heavy the turret was, this was no easy task. The Panther and Tiger B had an easier time of it, since there was a removable roof section around the driver's compartment, but the job was still far from easy.

Compared to this, the removal of the gearbox on Soviet medium and heavy tanks was a piece of cake, especially on the T-34 and IS-2. Another advantage of Soviet tanks was that if a shell or mine destroyed the front idler, one could temporarily wrap the track around the front road wheel. The tank partially retained its mobility as a result. On German tanks, where the drive sprocket was in the front, this trick wouldn't work.

Like with Porsche's designs, the suspension of the E-50 and E-75 was outside the hull.

Aside from the E-100, the E series contained the light E-10 tank destroyer which would serve as a replacement for the Jagdpanzer 38(t), a medium E-25 tank destroyer (replacement for the Jagdpanzer IV) and a "unified chassis". The medium E-50 and heavy E-75 tanks would use this chassis.

Krupp and Henschel worked on the E-100, but the suspension was worked on by Adlerwerke. Engineers from Klöckner Humboldt Deutz AG, or Magirus, worked on the E-10. Argus Motoren Gesellschaft m.b.H. worked on the E-25.

As for the E-50 and E-75, this is a more difficult topic. Adlerwerke is often named as their developer, but that is not the case. As with the E-100, this company worked only on the suspension. Information on the "unified chassis" is incomplete, and largely the product of speculation and fantasy.

The Adler suspension used springs instead of torsion bars.

Another little known fact is that the E-50 and E-75 duet was not the only alternative for the Panther and Tiger B. In April of 1944, Vereinigte Apparatebau AG, Rheinmetall-Borsig AG's design bureau, proposed its own suspension. It was essentially a modernized version of Aleksei Surin's suspension, which was used on the AH-IV tankettes, light Praha TNH and LT vz. 38 tanks, as well as a number of other CKD vehicles.

The difference between the two suspensions was that now the paired road wheels were interleaved. The difference between the prospective running gear for the Panther and Tiger B was the distance between the bogeys.

A diagram of the kinematics of the prospective Adlerwerke suspension.

The idea of Adlerwerke's engineers, led by Karl Jenschke, was different. Their design was closed to the suspension that was designed by Porsche KG. The difference was that Porsche's designers used a torsion bar, and Adlerwerke used springs. Jenschke claimed that this suspension was tested at MAN and gave good results.

Prospective Panther suspension by Vereinigte Apparatebau AG

The wheels here were also interleaved. The question of how many wheels there were per bogey has no answer. Most sources copy the sketch made by Jenschke in the spring of 1945, after he was taken prisoner by the Americans. There, he drive single road wheels. However, this decision was suboptimal from the point of view of weight distribution, and Porsche and Vereinigte Apparatebau AG doubled up their road wheels. It's likely that the E-50 and E-75 also had double road wheels.

A new suspension for the Tiger II. There's minimal difference between this variant and the one on the Panther.

According to the concept, the E-50 and E-75 would have nearly identical hulls, distinct only in armour thickness. There are no concrete numbers about what this thickness would have been. The numbers in the names indicated the weight class of the tanks, and since the E-75 would be 1.5 times heavier, the number of bogeys increased to four per side.

The information received by the Americans said that the weight reserve of the E-75 chassis meant that SPGs in the 80 ton class could be built on its chassis. This information gives additional room for speculation. There's no shortage to the vehicles that were "designed' on this chassis, but we must disappoint the "designers": a reserve and its use are two different things. As for the SPG with a 149 mm L/52 gun that is brought up when this project is discussed, its real mention dates back to documents from 1941 and applies to a completely different project, the VK 70.01.

Maybach HL 295, one of the descendants of the E-50 and E-75's engine.

The parameters of the E-50 and E-75's engine are also known. The V-shaped 12 cylinder Maybah HL 234 would be used. It was based on the HL 230, but the HL 234 output 900 hp at 3000 RPM. In order to make the engine more reliable, it could have been lowered to 850 RPM. The HL 234 had a special feature in the form of direct fuel injection. A turbocharger could also be installed, raising the power output to 1000 hp. The Maybach HL 234 R engine could serve as an alternative, but there is no data on it.

The engine would have been connected to a hydraulic 8-speed gearbox with a preselector and a 2-radius turning mechanism. The name of this gearbox was mentioned in the report on the Maybach HL 234: OG 40 12 16 B. A special feature of the E-50 and E-75's transmission was that the gearbox, turning mechanism, and final drives would have been built as a single unit. This saved up to a ton of weight and shortened the time to build the tank by 25%. According to calculations, the top speed of the E-50 was 60 kph and the top speed of the E-75 of 40 kph.


While there is some data on the engine, suspension, and hull of the E-50 and E-75, there is no information about the armament. This let the imagination of fans of alternative history run wild. However, if we take into account what little information we have and the overall tendencies of German tank building from the time, it turns out that most of these fantasies have few roots in reality.

One of the long guns that are frequently "mated" with the E series.

For starters, we must disappoint the daydreamers who put the Schmalturm, or "narrow turret" on the E-50. It was initially designed for the Panther II, and its significantly altered version would have been installed on the Panther Ausf. F. Those who put the Tiger B turret atop the E-75 will also be disappointed. Neither turret was going to be used on the E-50 or E-75.

According to information obtained by American intelligence, Krupp was supposed to design a new turret for these tanks. Like the hull, the turret designs for the two tanks would have been identical, with the only difference being the armour thickness and the armament. There is no other information about the unified turret, only that it would have an electric turning mechanism.

The latest "long arm". As with the previous weapon, it was never built in metal.

Let us discuss the topic of guns separately. British intelligence, which received information in a highly distorted state, created the myth that the Germans were developing new super-long tank guns. A typical example of this was the mythical 7.5 cm KwK L/100. There is also mention of an 88 mm gun with a 100-caliber barrel. There are three news about these guns: one good one and two bad.

Let's start with the good one. Research in the Bundesarchiv revealed designs of guns with barrel lengths of up to 130 calibers. This is the end of good news. These guns are labelled as "Pak" in the blueprints, so they were anti-tank guns. The date when these guns were designed is also striking: early 1943, whereas the main activity around the E-50 and E-75 dates to late 1944. Krupp's engineers also designed a 105 mm gun with a 100-caliber barrel, but it was also not a tank gun. In other words, these "grosse Schlange" have nothing to do with the E series tanks.

Installation of the 88 mm KwK 43 L/71 gun into the Schmalturm turret. You can't tell from the diagram, but the factory blueprint shows that in this case, the commander would have to sit on top of the gun breech.

Even if we assume that the aforementioned turrets were installed on the E-50 and E-75, this brings few good news to German tankers. Krupp worked on the installation of the 88 mm KwK 43 L/71 in the Schmalturm turret in November of 1944. It fit, of course, but the turret didn't get any roomier. The turret ring diameter was only 1650, and the gun barely fit, according to the factory diagram. The commander must have sat directly on top of the gun breech. The issue of loading was not discussed. The longer barrel would also have needed a counterweight in the rear of the turret.

Overall, Krupp's design was similar to the work done by TsAKB, led by V.G. Grabin, who managed to shove the 100 mm LB-1 gun into a stock T-34-85 turret. The results were the same as with the Schmalturm and the KwK 43: you can fire it, technically, but the crew was uncomfortable. Considering that this invention didn't move further than paper, the opinion of the German and Soviet militaries about such experiments must have been the same.

Sketch of the Tiger II with a 105 mm KwK L/68 gun. In order to get it to work properly, the gun would have to have two piece ammunition and a second loader. The Germans deemed both of those things unacceptable.

The situation with new armament for the Tiger B was even stranger. In November of 1944, Krupp prepared a draft for installing the 105 mm KwK L/68. As with the new gun for the Panther, the gun fit, barely. However, the one piece round for the 105 mm gun refused to do the same. The only way of shoving it into the turret would be to introduce a two piece round. This worked, and 20 shells could be carried in the turret. The rate of fire dropped drastically. However, this could be solved by adding a second loader.

Having though about this, the 6th Department decided not to build this tank in metal. This prospective gun for prospective tanks could only work in alternative history and in computer games.

Aryan Dead End

Many military history "experts" have the opinion that the Germans had high hopes for the E-50 and E-75. In reality, the Germans had better things to focus on than the E series in early 1945. The development of a unified chassis was in such early stages that it had no chance of mass production. According to the plans of German high command, the Pz.Kpfw. Tiger Ausf. B and Pz.Kpfw. Panther Ausf. G remained the main tanks of the Panzerwaffe. The Panther Ausf. F would have gone into production to replace the Ausf. G at some point in the future. In reality, the Germans were stuck in 1943, trying to polish up the same tanks, which were gradually overtaken by the enemy's designs.

Even if we imagine that the war in Europe lasted past May 9th, 1945, and that the E-50 and E-75 made it into the army, the Germans wouldn't have gained much, especially on the Eastern Front. In the best case scenario, they would have faced the T-44 and IS-3. If we include prospective Soviet tanks, the Germans' future turns grim. The first prototype of the T-54 tank, immune to the 8.8 cm Pak 43 from the front, entered trials in January of 1945. The decision to put either the IS-3 or the even more protected IS-4 into production was made in the spring of 1945. This isn't even including projects like the Object 257

One must note that Soviet tank designers made huge steps forward when it came to protecting their tanks without increasing mass. Their colleagues in Great Britain and the US were behind, but they were catching up quickly. One must recall that there was no shortage of funding in wartime, and new British and American tanks would have arrived much quicker had the war continued. In any case, the E-50 and E-75 were far from Wunderwaffe and would be, at best, no better than their opponents.

T-54 prototype, NIABT proving grounds, Kubinka, March 1945. Immunity to the Pak 43 from the front, a 100 mm D-10T gun, mass of 35.5 tons, and all of this was not just on paper.

More proof that the Germans designed themselves into a dead end comes from the history of the French AMX 45 medium tank. This tank, which later turned into the AMX M4, was a direct descendant of the E series. The French did not use its suspension, but the Maybach 295 engine was a relative of the HL 234. The dimensions of the hull were also similar. German engineers worked on the project. The result was a dead end. Even the engine power had to be decreased from 1000 to 850.

The Germans themselves went down a different road in the early 1950s. The new German medium tank project was much more humble than the massive E-50. The 30 ton tank had a torsion bar suspension, a crew of four, and very thin armour, even by late WWII standards. The concept behind the tank was closer to being a product of the American tank school than the German. Its dimensions were closer to that of the Soviet T-54 and T-10. The 37 ton Standardpanzer, better known as the Leopard 1, was built by the same companies that designed the German tanks of WWII.


  1. How in gods name would you fit 20 10.5cm shells into a Panther turret? Even for the entire tank 20 rounds just about fit, but the turret originally didnt even contain ammo to begin with, while having a smaller cannon. WTH is going on there? Tardis turret?

    1. read again they are talking about the Tiger II turret with a 105mm and 20 rounds, like the 88mm on in the Panther turret is would have barely fit. its not about the 105mm in a Panther turret

    2. Obviously "heat" was the reason, as everyone knows how concerned Adolf was with the fate of the planet, and being an advanced being, he foresaw the advent of global warming.
      So such machines were not at all allowable per his world plan.

      I mean, just look at his regimes work toward alternative fuels, and population control.

  2. "The 37 ton Standardpanzer, better known as the Leopard 1, was built by the same companies that designed the German wanks of WWII."

    "same company that designed the german wanks of WWII"

    "German wanks of WWII"

    I found this hilarious!
    I guess you really hit the nail on the head when it came to German tank design.

  3. T54 prototype 1 isn´t frontally proof vs 88mm PAK 43/KWK43. The single aspect which was immune was the glacis plate. Neither the nose plate nor the frontal turret aspect can be realistically expected to offer immunity vs 88mm Pzgr39.

    1. The turret sides are immune, too. In fact, the only vulnerable points are a straight-on shot to the turret face or mantlet, or a hatch hit.
      That's really small. I'd estimate less than 5% of the frontal area.

    2. No. The whole turret front, incl. mantlet area as well as the turret side of Mod. 1945 prototype turret can be penetrated by 88mm Pzgr 39 and 75mm Pzgr 40 (sides also by 75mm Pzgr 39). The lower front can be penetrated by 88mm Pzgr 39 (very close range, marginal) and Pzgr 40. Glacis was the only aspect immune frontally.
      The shot trap of the turret front with the extremely thin roof armor below will allow 75mm PAK 40 to knock out the tank frontally, too.
      The same weakspot will allow fairly easy HE knock outs as well.

    3. Are you considering that the turret side is only presented at an extreme angle from the front? It is already 150mm thick and is presented at greater than 60 degrees from perpendicular.
      In addition, even if we assume the bottom half of the turret is a shot trap, the top half isn't.

    4. True enough. I was considering, in agreement with high number of penetrations in the turret sides- that the turret doesn´t necesarely need to be pointing where the hull points to. Purely frontally, I agree, the sides will be immune due to acute angular exposure.

    5. It seems that side thicknesses given here are not from 1st prototype but from a later.

  4. "Installation of the 88 mm KwK 43 L/71 gun into the Schmalturm turret. You can't tell from the diagram, but the factory blueprint shows that in this case, the commander would have to sit on top of the gun breech."

    -such a statement suggests to me that somebody can´t read a factory blueprint / an engeneering drawing.

    In regard to the often suggested 105mm armament, one should keep in mind, under the caveate that presently known archival source evidence is thin admittedly, that the 1941-1942 projected 105mm KWK L/70 was eventually manufactured 1943 and turned into an experimental 105mm L/70 (firing either 15.6kg 10cm Pzgr. rot Gg. at 1025m/s or a new 18kg Pzgr L/4.3 at 965m/s). Krupp eying with a 105mm KWK following this work as an upgrade for the TIGER B seems logical, an L/68 barrel is required to obtain a mv of 950m/s with the heavy or 1000m/s with the light projectile, probably not a coincidence in this context. Such a gun would have been extremely powerful, moreso even than the 128mm L/55 in terms of performance and capable to reliably penetrate IS3 on all aspects (the penetration graphs end at 240mm RHA penetrated at 30° and 950m/s for the older and lighter 10cm Pzgr. rot Gg. This translates to in excess of 300mm RHA vertical penetration at this velocity, presuming the projectile is of high enough quality not to break up).

    1. "presuming the projectile is of high enough quality not to break up"
      Isn't "not being of high enough quality and thus breaking up" the story of Axis metallurgy after 1944?

    2. No. Projectile break up is the story of soviet ww2 AP ammunition, less so for western allies. The german AP quality was so drastically superior to both, that the USNPG reports 1944 and 1945 repeatedly suggested to study german AP metallurgy closely FOR THE INTENT TO IMPROVE US AP AMMUNITION.
      The soviets did the same later and eventually replaced their crap ww2 ammunition in the early 1950´s with a new APCBC-HE design (f.e. BP-412D, BP-471D) relying on the german ww2 Pzgr 39 technology.

    3. If you’re talking about the US high velocity tests of German 88mm Pzgr39/43 results vs. high angle armor were:

      3 7/16" (87mm) @ 55̊° Two complete penetrations. both projectiles fractured. Projectile fragments passing through plate. One partial penetration projectile fractured. 1016 m/s MV on two penetrations. 1009 m/s MV on 2.5" deep partial.

    4. Mobius,
      I referenced 30° and 0°. Not 55°. I guess You are familar with the differences. 55° results in base first penetration (only possible in mild steel and VERY SOFT armor) -otherwise the projectile always brakes up (You can´t harden the base or the filler will touch off causing prematures). It´s larger than the obliquity under which the projectile can be expected to stay intact.
      If You have the report, try looking for the entries for 0° and 30° obliquities, and compare US and german shell for details.

      In general, let me quote the conclusions:

      A. That the german projectiles had better penetration charackteristics against homogenious armor plate than the American projectiles.

      B. That the german had less tendency to shatter when fired against homogenious armor plate at high velocities

      It is recommended that the design features, hardness pattern and composition of the German armor piercing projectiles be studied for purpose of improving American armor piercing ammunition."

  5. The US 90mm HEAT shell could penetrate the frontal aspect of the T-54 at any range. So I might seem reasonable the 88mm would use more developed HEAT shells for a period of time.

    1. US HEAT also tended to fail to fuse at angles above 50 or so degrees. 1946 era HEAT would have been far worse at that.

    2. Instead of a generalization, one would need to discuss this on the specific details of the warhead design. The level of HEAT technology knowledge achieved in Germany during 1944/5 was cutting edge and head and shoulders above anybody else.
      The reason why MAUS and E100 were cancelled in 1943 was HEAT.

  6. Mobius,
    the german 75mm L/70, 88mmL/71 and 105mm L/68 rifled guns are all very high velocity guns, inducing a substantial degree of spin to the projectile. The application of HEAT warheads in this particular environment is suboptimal for them and this was realized by 1944, latest (studies pertaining the effect of spin rate, detonation speed, etc.).

    Development to increase attack of highly sloped armor for KWK /PAK guns was directed into development of a new Pzgr type instead, very blunt nosed, thickly capped and with windscreen. Experiments conducted with 75mm Pzgr of different ogive´s and the ideal cap shape were made during summer 1944 at the prooving ground of Hillersdorf.
    It´s not clear to me that a lot could be gained from these, as the solutions adopted for successful attack of 60° sloped armor entailed a trade off in penetration performance at 30° obliquity.
    However, the soviet´s preference of high hardness, highly sloped armor plate -tuned to be most effective against soviet uncapped AP- migth actually have helped APC a lot because the hard plates significantly increase normalization and inhibit ricochet of capped AP. Ricochet would be more common with less hard, more ductile plates (notice that HETZER´s glacis plate was not inferior- it was soft for a reason!).

  7. Critical Mass
    “ Ricochet would be more common with less hard, more ductile plates..”
    Makes an interesting theory but in practice not so much. In the Yugoslav tests of the 50s and 60s the softer 102mm@60̊ armor of the M47 could be penetrated by the 88mm PaK43 at 250 meters. While the harder 100mm@60̊ armor of the T-54 could not do so at any range.

    1. It´s not a theory, Mobius, it´s empirically prooven. Too much is made of the Yugo test.

      1st) according to german penetration charts, the 88mm PAK43 can´t be expected to penetrate more than 80mm-90mm RHA @ 60° and 1000m/s. The failure mode in these tests was ductile failure, the projectile always breaks up.

      2nd) well, the same gun did penetrate 90-100mm high hardness soviet cast armor @60° in soviet tests at down to 920m/s, and 90mm high hardness RHA at significantly less from soviet tests.

      3rd) it didn´t penetrate the T54 glacis AS COULD BE EXPECTED. The T54 manufacture shifted towards a more ductile armor material in the early 1950´s, which had 8%-11% less protection at 30° but ~10% better protection at 60°.

      4th) it did penetrate the M47 glacis. This could NOT be expected but is possible considering the problems the US had with 3" and 4" armor ingots for RHA plate. It´s very likely the plate failed by adeabatic shear or brittle failure. Notice the plate was soft, but this doesn´t necessarely mean it was also ductile.

      So either soviet cast and RHA were >20% inferior to german RHA (possible only for cast armor but not for RHA), or alternatively, the penetration was effected by shear failure, a low energy penetration, for which we have indications from the tests.
      The T54 glacis didn´t behaved "special", just exactly as could be expected from a Krupp trial plate.

      Notice, while there is a correlation between tensile trength and strain rate, it´s not an absolute autocorrelation and depends a lot on armor steel mix, section thickness, quenching temperature, cooling rate, re-tempering range and post tempering cooling.
      Soft armor steel needs to be quenched from fairly high temperature, and if cooling rates are slow enough- or the section thickness large enough to cause slow internal cooling rates- than even soft armor becomes brittle.

    2. Actually, not enough has been made of the Yugo tests. They use the v50 penetration criteria rather than the inconsistent Krupp criteria.

    3. Surely you already know that critical mass considers his own opinion more reliable than tests performed by contemporary experts.

    4. Mobius,

      the V/50 penetration criterium is a conformal definition for cross-country comparison. However, I am sure You are aware that the german penetration curves are not Krupp curves. Both Krupp and Rheinmetall had their own penetration curves, seperate form the official ones and based upon the company´s historical samples.
      While these are primary sources, they are company internal sources and therefore are less reliable than, say WaPrüf´s official penetration curves, tested for on the gouvernmental (speak: independent) prooving ground, not on the company´s one. I have leaked a set of these official penetration curves from my archive to You (and others) a couple of years ago and You´ve used it under Your own term "Datenblatt" since.
      These are "Durchschlag" curves, in which five out of five tests (no failure allowed) within a narrow velocity range have to completely penetrate a plate of known tensile strength in intact condition (up to ca. 40°) with the failure mode of the plate beeing ductile hole formation.
      Past 45°,when breakage sets in, the definition was that five out of five tests should result in fragments of the projectile up to and incl. the fwd bourrolet were to be recovered behind the plate. The failure mode of the plate under these conditions was dominated by plugging.

      The official german "Durchschlag" definition is way more severe than the conformal V/50 and represent a close to 2sigma confidence criterium.

      Whenever armor penetration is concerned, it´s not enough to know the velocity, obliquity and tensile strength of the plate but also the be able to identify the specific failure mode under which the plate gave way to -or resisted a penetration.
      That´s why I use to consider only tests, where information of the projectile damage and plate damage is included.
      This kind of information is not available in the Yugo tests, and this can and will lead people not familar with penetration mechanics to misleading conclusions.

    5. “Past 45̊,when breakage sets in, the definition was that five out of five tests should result in fragments of the projectile up to and incl. the fwd bourrolet were to be recovered behind the plate.”
      What is your source for this? It would infer there are two different standards for the same shell. The penetration graph would not be smooth at the transition angle but would have a shelf there.

  8. J. Sitz comments on practical experiences of the prooving ground work in Lilienthalreport 166(1943) and Hillersleben minutes (1944).
    The german anti tank projectiles were designed such that the velocity for penetration and the velocity for intact penetration fall together (extreme case: Projectile stuck in plate or even rebound in intact condition with no damage other than stripping of driving bands and nose covers).
    At obliquities of 40° and above, the variance and the delta between fragmented perforation and intact penetration increased. Also, the type of plate failure enlarged (ductile [slot formation] failure, adiabatic shear failure causing plugs or discs).

    Notice that they still required a 5 out of 5 success criterium, which is difficult to obtain when break up occurs once in a while.

    f.e. German official penetration curves give 95mm RHA @ 45° for the 75mm Pzgr 39 at ~960m/s.
    At the USPG, the projectile was succesful, sometimes at least, against 132mm RHA plate and stayed intact.
    132mm from US tests is much thicker than 95mm from german official penetration curves, don´t You think?

  9. "At the USPG, the projectile was successful" I'm not aware of a US 75mm/L70 PzGr 39 test. US data all seem to come from British tests.

    BTW, what is the MV of the 75mm Pak 40. Germans have it at 750 m/s and Russians at 770 m/s.

  10. I am sure the british had their own tests and shared them with the US but the US also conducted it´s own series of trials. For the matter in quetion, I am referring to trials conducted on feb. 6th & 7th 1945 at the Aberdeen Army prooving ground using US RHA plate made by Carnegie-Illinois (plate # TT-281 1/4). The gun was the 75mm L/70 KWK42 mounted on a captured Pz V. Project No. 5065 (574-P12-114). I have read the complete report.

    1. During these trials, they also compared their domestic 90mm M82 fired from an experimental, high velocity 90mm gun with the german 88mm Pzgr39 fired from PAK43**. Against 8" RHA plate, and normal obliquity, the 90mm M82 always broke up and didn´t managed to obtain a calibre sized hole through (just bulge) at 950.9m/s and 986m/s velocity.
      The 88mm Pzgr39 was stuck in the 8" plate at 914.7m/s (partial penetration, intact with nose through) and penetrated completely at 952.2m/s and 992.7m/s -without any damage.

      The turret of the improved, T54 obr.1951 was also tested ballistically at the NIIBT vs 90mm M82 at the soviet prooving ground (MV:930m/s), aiming for the horizontal perpendicular of the turret casting. A total of 28 hulls and turrets was tested (large sample). The limit of PKP (plugs and discs started on the backside) vs the 90mm M82 projectile was 900m -1400m, depending on the turret (large variance in quality of the armor castings, particularely against 100mm projectiles (600m - 2200m limit of PKP) indicate the presence of both, ductile and brittle turret castings). Considering that the M82 again broke up -as did all 100mm- and also was fired at lower initial velocity, it´s fairly certain to presume that the limit of penetration for the 88mm would be at substantially longer range than that obtained by the 90mm M82. This entailes also a higher probabiliyt of a limit of perforation (not obtained by either domestic soviet 100mm or US 90mm M82 projectiles).

      ** in my own opinion, the lot of Pzgr39 the US Army used to test at Aberdeen -unlike the 75mm Pzgr39 lot- was on the very low end of quality range variances. This is indicated by the poor performance vs 5" RHA @45° - with most projectiles shattering -unlike the 75mmPzgr39, which was better here than the 88mm Pzgr39. Such poor performing 88mm projectiles would not have been accepted for service after mid 1944 when the proof obliquity was changed from 30° to 45°.

    2. What page in Lilienthal-Gesellschaft 166 (1943) describes the +40̊ shell break up penetration criteria?

  11. the criteria isn´t described therein, Sitz points out the fact that all projectiles will break up at obliquities larger than 45° (p.112: "..., bei 45° dürfte ein Heilbleiben auch möglich sein und muß angestrebt werden, bei flacheren Winkeln werden die Geschosse zerbrechen.")
    The "G_D" criterium in use for official penetration curves dates back to the late 1890´s. It wasn´t extra discussed in ww2 as something new. There were three curves used:

    A) "Grenzkurve" - the velocity at which the projectile depletes all energy and either
    A1- projectile remians intact but is stuck in plate (not through)
    A2- projectile completely penetrates but in a broken condition

    B) "Durchschlagskurve" defines thee vlocity at which the projectile always completely penetrates (base completely through). The projectile may be broken up or stay intact (similar to A2 but A1 would never be considered "Durchschlag", slight difference)

    C) "Heilbleibkurve" defines the velocity at which the projectile always penetrates in a condition fit to burst (no damage allowed).

    B) was used by the Army, A) and C) by the navy (for homogenious Wh armor, the curves of A- and C fell together for the latest projectiles creating but not for KC). Only for acceptance of armor piercing ammunition, the Army criterium specified at the proofing angle (30°, later increased to 45°) that the projectile has to stay intact (Navy "heilbleib" criterium). For explorative trials to investigate penetration performances, the Army was using the older "Durchschlag" criterium, which is understandable because intact penetration was not obtainable for cal/plate(Krupp trial quality) ratios larger than ~0.8 (for Pzgr39) at 60°. And even if the projectile stayed intact, it cannot be expected do so for five consecutive attempts without failure occuring. In such shots, the limit of the plate is generally taken at that velocity, which insures perforation and the passage of the projectile, whole or in pieces, through the plate in agreement with the requirement for G_Durchschlag. This limit is higher than the theoretical one under conditions, where the projectile does not stay intact because of the energy consumed in the process of projectile break up but it was the only practicable way to secure comparative figures without deviating from the 5/5 requirements.

    1. So you are saying the criteria for a broken up shell is not in that report. And what about the definition “...should result in fragments of the projectile up to and incl. the fwd bourrolet...”? Where does that come from?

      “The Germans admitted quite definitely that they realized that their fuzes were by no means perfect and some went so far as to say they were bad; but they thought that if the shell broke up the critical velocity for penetration would be higher and that a shell entering an armoured vehicle, even if whole, would be lethal.” German Steel Armour Piercing Projectiles and Theory of Penetration report for B.I.O.S.

  12. I am not sure what fuzes have to do with it. Krupp developed a grace function of the fuze for very high obliquity but it required sheath hardened walls (only some lots of 10.5cm and 12.8cm had those). A stop gap was to harden the threaded grips of the fuze container in decrementally hardened AP.

    The problem with high obliquity is that mechanics of plate and projectile failure change rapidly.

    When I come across prooving ground results for high obliquity trials, such as carried out 1942-1944 in BA/MA RH 8/- files, a penetration was counted as "Durchschlag" only if either the whole projectile or fragments up to the forward bourrolet were found behind the plate at 60° and 75°. To identify the original 1890´s defintions of "Durchschlag" would take a couple of weeks in Freiburg, and I am not going to do this, for me it´s sufficient to know how it was done. It is essentially the correct approach because highly oblique impact vs relatively thin (<cal/plate ratio), ductile plate will result in a base first penetration, unless high hardness armor causes sufficient normalization to allow a nose first event (when associated with a lower strain rate in the plate -indicated by adiabatic shear failure rather than ductile slot formation-, this will cause a very substantial reduction of ballistic protection). Base first penetration will, of course mean that fragments of the base will be more commonly encountered behind the plate than fragments of the nose.

  13. Critical mass

    perhaps you can also post at...

    It would be great to have you discuss technical issues, thanks.

  14. I'm a little late, but what about this drawing waretmarked by Doyle showing a Panther turret on a E-50/75 hull? Just for reference?

    1. Placeholder, probably, seeing as how no data about the turret (aside from the bore axis height) is given.

    2. The turret wasn´t decided yet. I´d agree as placeholder. Considering that the new suspension offered more internal space, it´s likely they wanted to use the space as they opted not to make the hull smaller.

      Panther Ausf. F and Ausf. G would receive Schmalturm turret in mid 1945, with proposals to update to 88mm KWK 43.
      Claims from this article that the " the commander would have to sit on top of the gun breech" are not correct.

  15. On a sidenote, can we just take a second to appreciate how sexy the Panther II's suspension looks?