Is IS-2 early's front turret that vulnerable?

[JasonC]

Amizaur - Assuming everything you derived from the diagram is correct (which I believe), that puts the feasible penetration range of the 75L48 hitting the turret front at just under 1000 meters, or as low and 750 meters if production instances were routinely as thick as 115mm rather than the design spec 110mm.  In that range, in any event.  That is using the usual 50% penetration standard, so in CM terms at those range a substantial portion of hits would be partial penetrations only.

Which still seems long compared to the tactical evidence, which reports 88L56 and 75L70 penetrations to that distance and a bit more, but (so far) for 75L48 only short range and side penetrations.  I note that with 30 degrees of additional side angle to the plate, you'd expect the same round to only penetrate at 100 meters, which may account for much of the discrepancy.  Meaning, in combat it may have simply proved harder to get true flat hits on any of the plates than reading off a diagram and imagining a shot from straight ahead would tend to suggest.

Panzer IVs should not be routinely defeating IS-2s in heads up duels at 1200 to 1500 meters, in any event.

[Amizaur]

Jason, I understand what you wrote but I can't explain this. I can only speculate.

- Maybe hard 115mm armor resisted undermatched 75mm shells much better than "normal hardness" armor, so 100-115mm of it was equivalent of some 115-130mm of "normal armor" against 75mm shells. 

- To penetrate from 750-1000m from 7L48 quite small vunerable area (part of curved armor that is almost vertical) would have to be hit. Maybe such hits didn't happen or were not attempted.

- Maybe after the Germans estimated head-on range against IS-2 at some 100-300m,  PzIV commanders didn't even try to engage frontally at longer ranges, so no penetrations happened.

- Maybe there are no ~1000m front turret penetrations by 75L48 because nobody dared to engage Is-2 with PzIV _directly_ head-on (with IS turret at 0 deg side angle, IS gun aiming at the shooter) because it would be considered to risky/stupid/suicidal (shooter too easily spotted and fired back), so front engagements were attempted only with some side angle (when IS-2 gunner was looking elsewhere, not pointing at the shooter). 

In German (calculated) WaPruf tables of enemy tanks vunerability ranges they always included an additional 30deg side angle in calculations, which makes those ranges much shorter than expected head-on ones.

Unfortunately we could veriyfy that only if we knew about some unsuccesfull 75L48 hits at front turret vertical parts at 700-1000m range.

One more thing. If we find a range at which IS-2 front turret was vunerable to a Panther gun (both Russians and Germans give some ranges but they differ and we do not know for sure if they were found by actual test-shooting or just calculated) then we could easily find penetration ranges for 75L48 just comparing penetration tables of both, or better yet - shell velocity profiles. If front  turret of Is-2 mod 1945 prototype (reportedly 130mm thick, 20mm above designed thickness) was reported to be vunerable to Panther gun at 1100m then it would be vunerable to PzIV gun at... 0m. 

If we rescale the results by factor of 1,13 (=130/115) and 1,3 (=130/100) to estimate penetrations against 115mm mantlet and 100mm turret face of normal Is-2s, then we get 1700m/2200m for Panther gun and 500m/1100m for PzIV gun for mantlet/turret penetrations. I must admit that those results are not too convincing....  :). 

In the same report lower front hull plate (100mm cast at 30deg) was estimated vunerable to Panther gun from 900m. (That's probably close to Initial Penetration range because Russians tested their tank for protection). Official KwK42 30deg penetration from this range is about 87mm. So this plate even though being hard and 33% thicker than shell calibre, seem to resist against 75mm shell somewhat worse than German test plate.

And the same report suggest that front turret armor resists better than German test plate  - penetrating only 130mm of vertical armor from 1100m (criterium of initial penetration probably, so 50% penetration or 5_in_a_row penetration values would be even smaller). 

Either the turret/mantlet armor was much more resistant than hull armor, or something is wrong here.

I'm considering buying a portable leeb steel hardness meter, so I could check armor hardness level of various parts of armor of Russian tanks. That's much more expensive than the ultrasonic thickness meter I bought before, so I'm not sure if it's worth it. Do you think that such hardness measurements could add something valuable to the picture ?

 

Edited March 15, 2016 by Amizaur

[Michael Emrys]

I'm considering buying a portable leeb steel hardness meter, so I could check armor hardness level of various parts of armor of Russian tanks. That's much more expensive than the ultrasonic thickness meter I bought before, so I'm not sure if it's worth it. Do you think that such hardness measurements could add something valuable to the picture ?

What is the likelihood of hardness changing over time? Since I am not a metalurgist I don't know. Would weathering due to outdoor storage effect hardness?

Michael

[A Canadian Cat]

The actual hardness of the steel would not change with weather. The temperature would need to get a lot hotter to change that. But surface rust could make good measurements difficult. Rust actually expands the metal too so thicknesses measurements would be affected as well. So measuring any of this would need to keep that in mind. I don't know how a hardeness measurement is taken so I am not sure what effect, if any,  paint has either. I am sure @Amizaur will do his resach and tell us all about it.

Looking forward to it.

[Amizaur]

To measure hardness with portable leeb meter I would need a tiny (few milimeters) places of bare metal, clean of rust and/or paint. On most tanks I examined there happened small places stripped of paint and rust to bare metal (thousands of people/children climbed on them and some fragments of armor were almost polished with their of boots) so this should not be a problem. The leeb hardness meter uses a small, spring driven weight with tiny tungsten tip. The tip hits the surface of the metal and the response of the metal (how the tip/weight bounces) is measured, which can be converted to hardness level. It's not _strictly_ indestructive meter - the hardened tip of the weight leaves a small (fraction of milimeter) pit/dent on the metal surface, but the mark is so small that it's probably not visible untill you know where too look for it.

Good readings from ultrasonic thickness meter required a flat, smooth part of armor about 1cm in diameter, either without paint/rust or with only thin, good layer of paint. Finding such places on surface of crude casting is not easy, but usually possible. If whole surface was without paint and covered with rust, I would probably have to clean small fragments to bare smooth metal (so would need permission for that).

[c3k]

Okay, the information being gleaned here is great. Really. So...how much DOES a portable leeb meter cost?

[A Canadian Cat]

Cool @Amizaur thanks for that background.  Very interesting posts you have been making.  Thanks for that.

[Amizaur]

You are very kind for me, guys, nice to hear that. Thanks.

Cheapest portable leeb steel hardness meter - from about $300. 

examples:

http://www.aliexpress.com/item/Portable-Digital-Leeb-Hardness-Tester-Leeb-Hardness-Meter-Leeb-Hardness-Gauge-HM-6561/32263489896.html

http://www.aliexpress.com/item/Promotion-price-YHT100-Portable-Rebound-Leeb-Hardness-Tester-170-960-HLD/32606745968.html

 

 

Edited March 17, 2016 by Amizaur

[PhilM]

Someone in another forum posted two interesting photos of IS-2 after being captured by Germans and loaded onto a train. There are much more holes in this tank, from different ranges. Maybe they did some kind of test-shooting the wreck, before they decided to transport it to Germany.

The penetration highest up the turret side damages the very neatly applied - German - script (via Google: "Salvaged (?) by s. Pz. Abt. 506): the "n" in "von" ...

So presumably that shot at least is a test firing, after the vehicle was "salvaged" and the script applied?

If the penetration hole was already there, the "von" could just have been applied a little further to the left to avoid it?

[Michael Emrys]

Sharp bit of observation and deduction there, Phil. Sherlock would have approved.

Michael

[Amizaur]

I didn't notice that, good observation !