Armor quality of Panzer III and IV

[Peasant]

Today I've had an idea: the 37mm US gun attacking a 50mm plate is quite similar in scale to the 76mm gun attacking a 100mm plate on Tiger I. And we know that the latter had serious troubles getting through at even small obliquities like 20-30°, because the shells were breaking up.

So, I found this report on testing of M62 APC shells against high hardness armour and chose these entries:
roughly 312BHN plate(closest to the 320BHN nominal hardness of PzKfw.III front plates):



roughly 363BHN:



Using DeMarre to estimate the ballistic limits for the M51 APC against 50mm/20° I get 781m/s and 757m/s from the first and second case respectively.
These striking velocities are approximately equivalent to 350 and 500m, pretty close to 500-600yrds. given in this table:

[critical mass]

The 3 inches M62 APC shattering under as little as 20 deg obliquity represents a somewhat serious deficit in AP performance.
However, other US sources state that the M61 was good to 25 deg obliquity, presumably against softer, more regular US homogeneous armor, so it’s in the right ballpark, nevertheless.

[Peasant]

The 3 inches M62 APC shattering under as little as 20 deg obliquity represents a somewhat serious deficit in AP performance.
However, other US sources state that the M61 was good to 25 deg obliquity, presumably against softer, more regular US homogeneous armor, so it’s in the right ballpark, nevertheless.

Its likely that the data on M61 was obtained with service velocities for the 75mm M3 gun, as in under 2000fps which would also help the shell stay intact.

[critical mass]

Yes quite so. Lower velocity helps the projectile.
what I dont understand is why the US Army was ok with this sort of performance envelope at all. The US Navy had procured the Mk29 3inches APC since a long time by then. In comparative trials 1945, it was found to not suffer the same shatter issue as the Army M62.

The Army model copied a major calibre, Navy sheath hardening pattern- while the Navy model kept a more conventional decremental pattern.
The Navy was correct both in large and small calibre heat treatments and the Army somewhat failed to listen?

[Peasant]

Relevant information: https://www.forum.axishistory.com/viewt ... 9&t=248275

A word of caution:

"The results obtained are in most cases insufficient to build a complete tactical schematic of every unique armour layout present on the enemy tanks. But, the fact that the armour of german tanks is similar in ballistic resistance to domestic armour of the same type, gives the right to use additional data from the ballistic trials of domestic armour, a great body of which was collected during the many years of manufacturing and testing. This allows to improve our estimates of the level of protection of enemy tanks.

For computing [of the tactical diagrams] the ballistic resistance of the german RHA was taken as equal to that of the domestic high hardness armour for thicknesses up to and including 40mm and to domestic medium hardness armour for 50mm plates.

Resistance of the layered(shielded) armour was takes as equivalent to that of a single plate of the same thickness.

In particular this part seems to be the most relevant to this thread:

[critical mass]

I suppose soviet HHA was somewhat more resistent vs soviet domestic shot than german RHA, as it utilizes a more complete break up / shatter of the attacking projectile at low obliquities.

"layered" armor can mean different things. If laminated is supposedly meant, then its generous to the attacked plate, as the netto resistence of welded and/ or rivetted plates is somewhat lower. Only forged laminates delete any weakness (e.g. TIGER Ausf. E/H´s twin 40mm forged together turret side armor plates).

Spaced armor with air gap in between can be very, very unpredictable here. If the projectile breaks up on the skirting plates, the plate behind will have vastly superior resistence. The same is true for capped AP, getting stripped from nose covers. If the projectile just tumbles, the plate behind will have somewhat elevated resistence. Then, of course, the fuse can be activated early.

For comparison, 45mm soviet domestic test shot vs Mz-2 (later redesignated: 8S) HHA armor (note, the projectile schematic No´s differ, so does the results):

https://t34inform.ru/photo/Ar_01_12.jpg

30mm at 30°: 590m/s PTP (tested) and ca. 650m/s PSP (interpolated) -projectile acc. to drawing 0130
40mm at 30°: 740m/s PTP (tested) and ca. 770m/s PSP (tested) -projectile acc. to drawing 0130

[Peasant]

I suppose soviet HHA was somewhat more resistent vs domestic shot than german RHA, as it utilized a more complete break up / shatter of the attacking projectile.

"layered" armor can mean different things. If laminated is supposedly meant, then its generous to the attacked plate, as the nettor resistence of welded and/ or rivetted plates is somewhat lower. Only forged laminates delete any weakness (e.g. TIGER 1´s 2x40mm forged together, turret side armor plating).

Spaced armor with air gap in between can be very, very unpredictable here. If the projectile breaks up on the skirting plates, the plate behind will have vastly superior resistence. The same is true for capped AP, getting stripped from nose covers. If the projectile just tumbles, the plate behind will have somewhat elevated resistence. Then, of course, the fuse can be activated early.

There were no tanks with spaced armour examined here, the only instance in this document where this rule was applied(as far as I've seen) was for the 20+20mm side armour on the Pz.IV tank. And yes the writes were aware that this would likely provide less resistance than a single 40mm plate, but decided to be safe in their estimates.

[critical mass]

If that armor was *calcuated* based upon resistence aequivalence to soviet HHA and RHA, then the dangerous range enevlope at 0° would be generally underestimated, while at high obliquities, the calculated dangerous distance would be overestimated with the crossover ranging between 30 and 35°.
But then again, this refers only to RHA but in the time in question, some plating (particularely over the fwd arc) were not RHA but FHA, with differing properties.

Thats not a critique. In absence of exact understanding of the respective obliquity differences, which were only worked out in 1945, one has make presumptions. And its so logical, one bases them on data which one understands well enough.

[Peasant]

For comparison, 45mm soviet domestic test shot vs Mz-2 (later redesignated: 8S) HHA armor (note, the projectile schematic No´s differ, so does the results):

https://t34inform.ru/photo/Ar_01_12.jpg

30mm at 30°: 590m/s PTP (tested) and ca. 650m/s PSP (interpolated) -projectile acc. to drawing 0130
40mm at 30°: 740m/s PTP (tested) and ca. 770m/s PSP (tested) -projectile acc. to drawing 0130

Things could've changed a lot in 2 years. Further developments of 8S steel in response to the need to simplify production and possible alloying element shortages during some time periods could've changed these values drastically(probably for the worse). Thankfully the document had this helpful table in it:

[critical mass]

Yes. That helps a lot. It also directly associates to the test projectile specimen in question (acc. to drawing 2-05013). Considering the rather wide range of different ballistic results just by substituting another 45mm test projectile, this carries significance.

[Peasant]

By the direction of People's Committee of the Armaments(НКВ) the development of the high powered 45mm gun was assigned to the Special Design Bureau No. 172 (made up of political detainees) in September of '42. Working together with Design Bureau from the factory No. 235, they took as the base the barrel and the recoil mechanisms of the 45mm AT gun M-42 and developed a variant for mounting in tanks. New gun was assigned index BT-42. From its field predecessor and the 20K gun BT-42 was differentiated by its very compact layout and the presence of a horizontal wedge breechblock (all previous "forty-fivers" had vertical wedge breechblock). In 1943, after completing the required trials program, the gun was recommended for accepting into service, but the time of T-70 was already ending. There were completed between 2 to 7 BT-42 guns, two of which were mounted in [T-70] tanks with one man turrets.

By the orders of People's Committee of the Armaments(НКВ) and People's Committee of the Heavy Industry(НКТП) during the begining of 1943 the SDB No.172 redesigned the design of the BT-42 for installation into T-80 tank. Because the maximum elevation angle of the gun in T-80 reached 60° and over, a new elevation mechanisms and recoil system were design. New gun received index BT-43 and was accepted into service. But because the serial production of the T-80 tanks was cancelled, BT-43 was never serially produced. Overall only two prototypes of this gun were made, that differed between themselves in small details.
During the spring-summer of 1943 SDB No.172 was working on a design of a tank mounted automatic AA 45mm gun with ballistics of M-42.

Original quote:

По заданию НКВ разработка 45-мм танковой пушки большой мощности была поручена ОКБ № 172 (политзаключенные) в сентябре 1942 г. Работая совместно с КБ завода № 235, они взяли за основу ствол и противооткатные механизмы 45-мм противотанковой пушки М-42 и разработали ее танковый вариант. Новое орудие получило индекс ВТ-42. От своего нолевого собрата и орудия 20К ВТ-42 отличалось очень плотной компоновкой и наличием горизонтально-клинового затвора (все предыдущие «сорокапятки» имели вертикально-клиповой затвор). В 1943 г. после проведения необходимой программы испытаний орудие рекомендовали для принятия на вооружение, но звезда Т-70 уже закатилась. Всего было изготовлено от 2 до 7 шт. орудий ВТ-42, два из которых установлены в танки с одноместной башней.

По распоряжению НКВ и НКТП в начале 1943 г. ОКБ № 172 переработало конструкцию ВТ-42 для установки в танк Т-80. Так как максимальный угол возвышения орудия в Т-80 достигал 60° и более, для орудия заново спроектировали подъемный механизм и накатник. Новая пушка получила индекс ВТ-43 и была принята на вооружение. Но ввиду прекращения выпуска тапка Т-80. ВТ-43 серийно не производилась. Всего изготовлено два опытных образца ВТ-43, отличавшихся в деталях.

Весной-летом 1943 ОКБ №172 проектировало автоматическую танково-зенитную 45-мм пушку с баллистикой М-42.

Source: https://www.twirpx.com/file/2339932/

The trials where the Stug III was fired at by a "45mm gun Mod.42 installed in the T-70 tank" took place somewhere in the September-Oct of the 1942, which fits into the timeline of its development: https://imgur.com/a/8D5RxTF

[Peasant]

D.T.D. Experimental Report
A.T. No. 113
Parts I, II, and III
Project No: A.3305
Trial No: X426
File Ref: 160/78/2
Report on Firing Trial
against Pz.Kw. Mk II. Model J
D.T.D. , No. 2221. Held at S. of E. Range. Shoeyburness, on 15th, 16th, 17th, 18th, and 23rd of February. 1943.

British seem to be more thorough, not just relying on notch tests.

Germans cut alloy content in mid 1942 so these tests should show flaws in armor, according to Flawed armor theorists. I will not provide a shot by shot tabulation of the weapons fired. 2lber, 2lber Littlejohn, 57mm, 25lber. I will just post conclusions of the 106 rounds fired at this single Pz.Kw III Model J.

First. Littlejohn. After firing at upper visor glacis with 5 regular 2lber and firing at nose with 4 regular 2lber.

Upper Visor FH addditional armor over Machine Quality(RHA) plate.
Angled upper nose FH Armor.

" (a) On visor spaced assembly, against additional M.Q. Plate, front of tank normal to attack.

Two rounds were fired. Both projectiles broke up on the front plate, the broken shot producing a smooth bulge in the visor plate at the rear."

" (o) Upper sloping nose plate, attack normal to plate.

Both impacts, produced external scoops 21/2" to 3" long, and 3/4" to 7/8" deep, with a smooth bulge at the rear."

2 pdr A.P.C.B.C. attack
Lower Nose Plate, normal to front of vehicle

" The plate appeared to be of good quality and resisted the attack satisfactorily without flaking at the rear or cracking at the face."

Main Hull side plate, at 31 degrees.

"The plate was ductile and did not flake at the rear."

Main hull at 40 degrees.

"The armor appeared to be of good quality, being ductile and free from flaking."

Hull Superstructure

"The difference in favour of the superstructure is accounted for by the fact it is face hardened."

"3. A review of the results under 6-pdr. attack indicates clearly the inability of this vehicle to withstand this attack."

Source: http://www.tank-net.com/forums/index.ph ... ntry678690

[Peasant]

Since, as these tests show, the Sherman's 75mm could be defeated by the spaced armour arrangement of the late Pz.IIIs. So I wonder, if soviet 76mm could be defeated as well?

The M66A1 fuze used in the M61 shell has the delay of 0,016s. while the soviet MD-5 fuze, has even less, between 0,003-0,010s.

Therefore, possibly, the late Pz.IIIs on the Eastern Front had a chance of not getting blown up by the first hit from T-34s gun, even at normal combat ranges.

[Mobius]

Since, as these tests show, the Sherman's 75mm could be defeated by the spaced armour arrangement of the late Pz.IIIs. So I wonder, if soviet 76mm could be defeated as well?

The M66A1 fuze used in the M61 shell has the delay of 0,016s. while the soviet MD-5 fuze, has even less, between 0,003-0,010s.

Therefore, possibly, the late Pz.IIIs on the Eastern Front had a chance of not getting blown up by the first hit from T-34s gun, even at normal combat ranges.

I don't see any connection to fuse speed.

[critical mass]

Fuse delay is not enough. The fuse, too needs to stay intact during penetration AND the shell body needs to stay undamaged (no crack through to the cavity).
Hitting a relatively hard target approaching 0.8-1.0 cal/D, or a softer target at elevated velocity will break up the projectile before any fuse action can detonate the HE element.

the shelks were ok for 0.5cal/t ratio and medium velocity, only. The HE is pretty wasted here.