THE 76 MM GUN M1A1 AND M1A2: AN ANALYSIS OF U.S. ANTI TANK CAPABILITIES DURING WORLD WAR II

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Re: THE 76 MM GUN M1A1 AND M1A2: AN ANALYSIS OF U.S. ANTI TANK CAPABILITIES DURING WORLD WAR II

Post by Mobius » 06 Feb 2018 00:20

In other tests
Comparative Effectiveness of Armor-Defeating Ammunition
Ballistics Research Laboratories Aberdeen Proving Ground
13-16 November 1951
Shows that 3" @ 55° Cast homogeneous 280 BHN is penetrated at 2315 f/s equivalent to 1850 yds.
At the same time 4" @ 55° RHA 280 BHN is penetrated at 2742 f/s equivalent to 225 yds.
3.5" armor could be expected to fall in between.
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Re: THE 76 MM GUN M1A1 AND M1A2: AN ANALYSIS OF U.S. ANTI TANK CAPABILITIES DURING WORLD WAR II

Post by Mobius » 06 Feb 2018 03:30

From Terminal Ballistics Data III 1945
Granted US data graphs are normalized to 237 BHN armor.
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Re: THE 76 MM GUN M1A1 AND M1A2: AN ANALYSIS OF U.S. ANTI TANK CAPABILITIES DURING WORLD WAR II

Post by Yoozername » 06 Feb 2018 13:10

This analysis by the US shows the Tiger I supposed vulnerability to US weapons. Evidently, they thought the Tiger had varying protection, as it probably did. Just posting this since it was brought up earlier. The Tiger had better frontal turret armor than hull armor (as a tank should IMO). Making a hull down Tiger a great threat.

I believe the Tiger I had 50-60mm (?) thick armor on the very steeply sloped frontal armor between the lower and upper hull. I am not sure why they would do this since the slope would give great protection, and that weight of armor could have been better applied to the upper hull. I read that any damage to the Tiger's 'transmission' components meant a lengthy multi-week vacation off the line. Perhaps needing a turret removal to access the components. Maybe a reason that the extra tracks were on the lower frontal hull.

Image

The angle of 25 degrees shows a large increase in protection against these US APCBC projectiles

Image

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Re: THE 76 MM GUN M1A1 AND M1A2: AN ANALYSIS OF U.S. ANTI TANK CAPABILITIES DURING WORLD WAR II

Post by critical mass » 06 Feb 2018 13:47

Mobius,

The tables You show are instructive for what *could* be obtained with high quality, specially made trial T33 projectile lots, which received a lot of extra QC care. However, from mass production (mostly post ww2), the US Army -unlike the prooving ground division- was not procuring T33 of this quality and this is evidenced by the acceptance test data I provided in my previous memo. The penetration graphs are based upon a projectile quality which wasn´t available for service. The problem is that the service people believed these numbers at face value. I believe all people thought the T33 would really defeat X.Y armor on a reliable base in the scale indicated by the 1945 tables, which come from a very limited set of trial data. And that´s exactly the failing here.
Once some time after VE-day there were enough T33 acceptance test data accumulated to demonstrate that the graphs were based upon a shell quality which was not actually procured under the specifications something had to be done and a number of analytical projects dealing with kinetic energy penetrators were started to explore and quantify the performance.
That´s why the 1958 data were normalized against all projectiles which were procured at this time, including a large body of service mass production acceptance tests. This is as good data as You can realistically expect from 1944-1954 period T33 production. Unlike previous tabulations, their data are all quantified, You see condition, definition, sample size and significance level in addition to AB(L) and You get the information as how the projectile behaved in these trials (intact-break up - shatter).

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Re: THE 76 MM GUN M1A1 AND M1A2: AN ANALYSIS OF U.S. ANTI TANK CAPABILITIES DURING WORLD WAR II

Post by Yoozername » 06 Feb 2018 13:54

I believe this is the document that Mobius is posting from. From January 1945.

http://www.lonesentry.com/manuals/90-mm ... index.html

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Re: THE 76 MM GUN M1A1 AND M1A2: AN ANALYSIS OF U.S. ANTI TANK CAPABILITIES DURING WORLD WAR II

Post by Mobius » 06 Feb 2018 16:04

Critical mass that is an interesting theory but the T-33 is an M77 bullet that had a windscreen. As they stopped producing M77 when the T-33 replaced it. But the ABL of the M77 vs 3.38" @55° armor is 2642 only 41 f/s difference than the T-33 results. (Windscreens have a small effect in increasing limit velocity.) This would seem to point to the overall quality of the T-33 not to have changed.

Yoosername, the graph was from part 2 from here.
http://cgsc.contentdm.oclc.org/cdm/ref/ ... l8/id/2375

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Re: THE 76 MM GUN M1A1 AND M1A2: AN ANALYSIS OF U.S. ANTI TANK CAPABILITIES DURING WORLD WAR II

Post by critical mass » 07 Feb 2018 18:30

In principle, the projectile body of the T33 was a plain vanilla M77. However, it should be kept in mind that the projectile was re-heat treated before beeing fitted with a cap. After retreatment and recapping, it had to pass acceptance tests, before beeing issued to service. The original tables in Terminal Ballistics II and III are only partially based upon penetration data from firing trials and partially upon computation by the then in place formula for armor penetration. For the T33 at 55° high obliquity, they used only the trial data in OCM item #26320 and extrapolated the curve based upon the formula. This single test did not return a reliable dataset as it turned out later.
NBL =2492fps (small dataset) and ABL=2682fps (302 datapoints, large sample )are 190fps apart from each other. The difference is >200fps if You factor in that the former is supposed to be NBL (majority of fragments behind plate) and the latter is ABL (complete hole through achieved, no fragments behind plate).

That´s why large scale tests are relevant if You want to expose the range of performances. In limited tests, it can go up or down but with sufficient sample size, the modus of the distribution becomes discernable. The problem is that often, we only have few tests for certain conditions but litterally thousends for another.

You are right about the windscreen effect. It´s there but not large. Some designs intended to minimize the effect (f.e. lightweighted ballistic caps made aluminium in Krupp naval L/4.4 Psgr.) but with tank projectiles, steel windscreens are prevalent.

Generally, at high obliquity, shatter isn´t a bad feature. Shatter inhibits ricochet attempts of the projectile. High oblique ricochet attempt always follow the same logic: the projectile digs into the plate, driving away material with it´s shoulder and body. While doing this, the plate exerts a force to the projectile which tends to deflect the nose away from the plate because the nose is in contact with the plate and well forward of the centre of mass of the projectile creating a lever. Eventually, causing it to re-emerge on the plate surface and ricochet off (no normalization!), leaving a long gauge, sometimes even a slot in the plate. If the projectile digs in considerably deeper than the centreline of the plate before the force causing it to turn away did alter it´s path too much, then suddenly the plate will have more resistence at the surface section and less material resistence on the innerside of the plate. Again, shoulder is displacing material and the plate will exert a force against it. But the force it can apply is in relation to the material strength of the backing and there is less backing twoards the innerside than towards the surface. This forces the projectile to follow the path of least resistence and be turned towards the plate´s perpendicular as it re-emerges at the innerside of the plate. This causes an S-shaped penetration channel, if the material is ductile enough to exhibit plastic deformation failure and the projectile strong enough not to break up/shatter. The turn towards the perpendicular at the plate´s innerside i what people incorrectly call "normalization".
This S-shaped path is a major cause for why more resistent, capped AP have higher ballistic limit in 45°-70° obliquity range than shattered projectiles. Additionally, the double base slam experienced by the projectile will often render the fuze blind. Shatter also invalidates the fuze but lineraizes the path by trying to overcome shear resistence. Plastic deformation is virtually impossible and the plate will exhibit shear failure.
Last edited by critical mass on 08 Feb 2018 11:04, edited 1 time in total.

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Re: THE 76 MM GUN M1A1 AND M1A2: AN ANALYSIS OF U.S. ANTI TANK CAPABILITIES DURING WORLD WAR II

Post by Mobius » 07 Feb 2018 22:45

The alternative explanation is the US test armor is superior to the Panther tank armor of the same thickness.

If we look at the
THE US FIRST ARMY TEST AT ISIGNY: 12-30 JULY, 1944

8) 90mm Gun, M1A1, AA
AP M77 will penetrate front glacis slope plate up to 600 yards, the gun mantlet up to 1,000 yards and the turret up to 1,500 yards.
We find that the terminal velocity of a M77 is 2363 ft/s at 600 yds. Whereas the 1958 test summary says its ABL for 3.38" test armor is 2642 ft/s.
In the 'Armor piercing ammunition for gun, 90mm, M3" PDF a clean penetration from a T33 is shown at 1000 yds further adding weight to the idea.

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Re: THE 76 MM GUN M1A1 AND M1A2: AN ANALYSIS OF U.S. ANTI TANK CAPABILITIES DURING WORLD WAR II

Post by critical mass » 08 Feb 2018 10:45

Yes, that is possible, too. Individual plates have a variety of performances like shot had.

I have also seen conflicting evidence that US RHA was inferior. At the end of ww2, some tests were made with german 75mm and 88mm Pzgr39. It occurred during them that US Carnegie made RHA plate, 5 3/16" (132mm) thick, at 45° when tested by 75mm Pzrg39 fired from PANTHER in USAPG tests, was completely perforated (with the projectile intact) with an NBL=3127fps (953m/s). The straddle obtained at the prooving ground was tight: At 3099 fps (944.6m/s) the projectile ricochetted of (intact!) after making a long, 3.75" depp gauge, while at 3155fps (961.7m/s) it perforated clean.
This plate also resisted 88mm Pzgr39 at 3211fps (due to projectile shatter). And a plate of the same manufacturer, 6.0" thick, resisted 90mm M77 & T33 at 30° up to the highest tested velocity of 3220fps and 3244fps, respectively (all projectiles shattered). So I am quite sure we cannot say it was just a poor plate.

I notice that the official german penetration curves, such as those of Lilienthalbericht 166 allow only 95mm RHA at 950m/s penetration @45° for the 75mm Pzgr39. By the rules (G(p) = 0.92 G(d)), 105mm RHA would have sufficed to stop (no holing) this projectile. But 132mm is considerably thicker than 102mm, and the difference is large enough to constitute not just merely a quibble. Now, we might infer that the 75mm Pzgr39 was just exceptionally good. It might indeed be part of the explenation, in case we could verify that the Pzgr39 lot was from >1944, and thus had to pas 45° specification acceptance tests. But information in the sources is absent to this detail.

Putting these numbers into prospect, the M26´s frontal glacis is just 4" cast at 43°. Thus, the frontal vulnberability of the glacis of the PANTHER vs 90mm T33 and vice versa vs 75mm Pzgr39 ranges between lower and no worse.

My preliminary interpretation is that the Panther plate tested indeed wasn´t of as high standart as the german trial RHA plate was, but whether or not this is a general occurance need to be verified. Of course, from this it follows that, when judging 90mm T33 performances, it is necessary to point out that the range and velocity of penetration given for 55° obliquity in terminal ballistics penetration graphs are valid only for sub quality armor.

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Re: THE 76 MM GUN M1A1 AND M1A2: AN ANALYSIS OF U.S. ANTI TANK CAPABILITIES DURING WORLD WAR II

Post by Zinegata » 14 Feb 2018 04:26

The problem - as with the vast majority of penetration vs armor studies - is that it does not account for the simpler reality that tanks in combat will simply fire a second time (and likely hit the same spot if the target has not moved) if the first shell bounced. And shells repeatedly hitting the same rough location will cause cumulative damage to the armor plate; leading to either internal spalling damage or even later outright penetrations. This is why ease of target acquisition and accuracy when firing is a more important measure of an anti-tank weapon's ability to take on an enemy tank than any other factor; yet people who study tank guns based on lab tests (often de-mounted from the tank) keep seeking to draw broad conclusions about how so-and-so tank cannot beat so-and-so tank based on their gun and armor penetration findings.

Moreover, I would note that the Kubinka tests against the Tiger II revealed that even HE shells could cause spalling severe enough to start an internal fire - which is a function of both thicker plates being more vulnerable to spalling and bad detail design on the tank's internal components. The problems were severe enough that the Tiger II vs IS-2 book claimed that the Germans eventually had to install spall liners on the Tiger II - which proved ineffective anyway which is why the crews started taking ammunition off the turret instead to facilitate faster bail-outs.

Which should show that making broad conclusions about a tank's survivability based on armor thickness alone is also largely myth-making. For an armor to be good it has to be resistant to both penetrating hits and spalling; and when a penetration or spall _inevitably_ occurs then the tank should still remain mobile (to allow the tank to get out of the kill zone) or at the very least not brew up to allow the crew the chance to bail out. Unfortunately it's very rare that entire tanks are actually tested in this manner (unlike modern civilian cars which are thrown into various types of collisions to test its safety) in favor of arguing over test data.

Anti-tank combat is a systems event, of which one or more shells striking the armor plate is but part of the overall story. It does the tank no good if the first shell strike technically did not penetrate but a minor spall sets an ammunition shell on fire leading to a catastrophic explosion inside the tank that kills the whole crew; or if the first shell causes the engine to conk out leading to an easy second shot on the same spot that causes a penetration. Folks really need to look at far more than just penetration tables to understand how tank vs tank engagements actually work; and why tanks with technically inferior gunpower and armor actually win much more often than not.

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Re: THE 76 MM GUN M1A1 AND M1A2: AN ANALYSIS OF U.S. ANTI TANK CAPABILITIES DURING WORLD WAR II

Post by Ulater » 14 Feb 2018 10:51

Moreover, I would note that the Kubinka tests against the Tiger II revealed that even HE shells could cause spalling severe enough to start an internal fire - which is a function of both thicker plates being more vulnerable to spalling and bad detail design on the tank's internal components.
Considering that "spalling" was entirely external and said Tiger II had its transmission removed, the fire had no source to start from, if it existed at all.
The problems were severe enough that the Tiger II vs IS-2 book claimed that the Germans eventually had to install spall liners on the Tiger II - which proved ineffective anyway which is why the crews started taking ammunition off the turret instead to facilitate faster bail-outs.
Was the turret ammunition not removed based on ample practical experience of the tank brewing up when penetrated in the turret?

I would also like to hear more about these spall liners.
Which should show that making broad conclusions about a tank's survivability based on armor thickness alone is also largely myth-making. For an armor to be good it has to be resistant to both penetrating hits and spalling; and when a penetration or spall _inevitably_ occurs then the tank should still remain mobile (to allow the tank to get out of the kill zone) or at the very least not brew up to allow the crew the chance to bail out. Unfortunately it's very rare that entire tanks are actually tested in this manner (unlike modern civilian cars which are thrown into various types of collisions to test its safety) in favor of arguing over test data.
Losses in tank crews inside tanks were minimal in WW II. Suprisingly even in tanks that combined ammunition, fuel and crew in one space, to some degree.

Anti-tank combat is a systems event, of which one or more shells striking the armor plate is but part of the overall story.
Of course it is a system event.

Thats why comparing the destructive effect of a high-calibre HE shell without taking the abysmal rate of fire and poor means of target acquisition of the vehicles that are using it is a bit foolish.

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Re: THE 76 MM GUN M1A1 AND M1A2: AN ANALYSIS OF U.S. ANTI TANK CAPABILITIES DURING WORLD WAR II

Post by Sheldrake » 14 Feb 2018 12:21

Zinegata wrote:The problem - as with the vast majority of penetration vs armor studies - is that it does not account for the simpler reality that tanks in combat will simply fire a second time (and likely hit the same spot if the target has not moved) if the first shell bounced.
What is the evidence for that happening? It isn't mentioned in the 21 AG ORS studies. Variations in propellent burning vibrations on the platform and changes in the wind strength and direction lead to a Probable Error of Range. It is quite hard to put two rounds in the same spot.

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Re: THE 76 MM GUN M1A1 AND M1A2: AN ANALYSIS OF U.S. ANTI TANK CAPABILITIES DURING WORLD WAR II

Post by Ulater » 14 Feb 2018 12:44

What is the evidence for that happening? It isn't mentioned in the 21 AG ORS studies. Variations in propellent burning vibrations on the platform and changes in the wind strength and direction lead to a Probable Error of Range. It is quite hard to put two rounds in the same spot.
And that is not even taking into account the human error - the ability of the gunner to range and correct accurately.

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Re: THE 76 MM GUN M1A1 AND M1A2: AN ANALYSIS OF U.S. ANTI TANK CAPABILITIES DURING WORLD WAR II

Post by Yoozername » 14 Feb 2018 14:17

'simpler reality'??? A better reality is the technical aspect of dispersion. Very range dependant. And I suspect that as the war went on, tankers would react to being hit no matter what armor they had. That is, I would not be surprised if a driver had a 'SOP' to reverse if hit.

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Re: THE 76 MM GUN M1A1 AND M1A2: AN ANALYSIS OF U.S. ANTI TANK CAPABILITIES DURING WORLD WAR II

Post by Mobius » 14 Feb 2018 14:35

Also, counting on long range hits with HE is optimistic as HE shells did not have tracers. So correcting for a miss would be problematic.

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