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 Sheldrake » 02 Feb 2018 10:30

Mobius wrote:
Sheldrake wrote: Its also worth noting that 6Pdr APBC and APDS penetrated the mantlet and a hit pon the lower mantlet would be likely to penetrate the hull roof and ammunition bin and cause a cordite fire.
You'll have to point out which 6Pdr penetrated the mantlet on a fair hit. One penetrated through the gun sight.
That isn't the point. I don't dispute that the 6 pdr should not penetrate the frontal armour of the panther, but there were vulnerabilities that allowed for the occasional success. Reference to "fair hits" reminds me of Murphy's Law and the "lucky" torpedo strike on the Bismarck. If the design of the ship left the stern 10% of the hull vulnerable to catastrophic damage to steering, was it just luck or a design fault?

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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 » 02 Feb 2018 13:43

It was both. The better you can aim at the weak point, the better the results. But, in a typical long range situation, where you are aiming for the vertical and horizontal parameters a target presents (I hate when people say 'center of mass'), you are bowing to the God's of Statistics.

I don't know if any WWII AFV that was uniformly armored so as to have equivalent protection with a particular facing. Something like the Hetzer had weaker lower hull armor on it's front. Is it a design 'fault'?, or is it a design consideration that most strikes will not be there? The Hetzer (if I can call it that), had a low profile to begin with, given that terrain could be blocking the area, and the lower hull being small, and aiming for it could result in a miss, both the user and hostile opponents have to live with it. I am not defending the Panther turret BTW, I think it was bad to begin with and the Germans accepted it as the defacto manufacturing design. Similar to the Panzer IV design, in that once they were rolling off the plant's floors, they could not stop the process to take advantage of battlefield experience. Perhaps the Tiger II turret showed the most 'lessons-learned' with its narrow front and superior mantlet.

The Hood certainly made the design consideration for speed over armor (like a M18 Hellcat), and paid for it certainly. The Bismark was damaged before the strike on its steering. I assume you mean the steering? I am not sure that could have been avoided. It was a lucky hit in an area that perhaps can't be armored that well, something like a strike on a optics hole on a mantlet?

But getting back to the topic, that is this pseudo-report, it never mentions the issues with the gunpowder and the ammunition being changed even though they include a cutaway that shows the later version of the ammunition. I have mentioned it before and the 3 inch gun ammunition could possibly have taken a bigger charge (cutaways show the void inside). The Soviets even mention this when they tested theirs. But, could the US projectiles withstand greater velocities without breaking up? Especially when striking sloped armor?
Last edited by Yoozername on 02 Feb 2018 14:02, 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 Yoozername » 02 Feb 2018 14:02

Richard Anderson wrote:
Mobius wrote:The 17 pdr had a MV of 2900 f/s and a length of 55 calibers. The 77mm had a length of 52 calibers and a MV 0f 2575 f/s.
http://www.wwiiequipment.com/index.php? ... &Itemid=58
Indeed. And the 3" and 76mm M62A1 APC fired from the 3" 50 caliber Gun and 76mm 52 caliber Gun generated a Mv of 2600 fps. The 76mm did it with 3.62 pounds of FNH propellant, the 3" with 4.62 pounds of NH propellant, and the 17-pdr with 9 pounds of propellant. I do not see how increasing the 76mm by three calibers to 55 without increasing the propellant would somehow give it 300 fps greater Mv from the M62A1, matching the 17-pdr. Or how the same would somehow generate 400 fps greater Mv from the T4E16 HVAP.
It is an interesting issue. I brought this up in another thread. Basically, how can the 76mm and 3 inch have the same velocity, firing the same projectile, when the 3 inch has that much more powder? Technically, I would look at the rifled lengths.

I suppose the the British weapons, with same projectile but different powder weights and different barrel lengths can also give insight. Obviously, the 17 pdr. projectile weighs more than the US 76.2mm projectiles.

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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 » 02 Feb 2018 18:09

Sheldrake wrote:Reference to "fair hits" reminds me of Murphy's Law and the "lucky" torpedo strike on the Bismarck. If the design of the ship left the stern 10% of the hull vulnerable to catastrophic damage to steering, was it just luck or a design fault?
Tell it to the Prince of Wales.

Increasing the barrel length 5 calibers might get you something like the 75mm PaK40. The L43 had a MV of 740 m/s. When firing the L48 it had a MV of 750 m/s. So you might expect a 10 m/s or 33 ft/s gain.

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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 » 02 Feb 2018 18:51

Yoozername wrote: I don't know if any WWII AFV that was uniformly armored so as to have equivalent protection with a particular facing. Something like the Hetzer had weaker lower hull armor on it's front.
The Tiger might be one of the more evenly armoured tanks

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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 Richard Anderson » 02 Feb 2018 19:05

Yoozername wrote:It is an interesting issue. I brought this up in another thread. Basically, how can the 76mm and 3 inch have the same velocity, firing the same projectile, when the 3 inch has that much more powder? Technically, I would look at the rifled lengths.
It is odd, since as I understand it FNH, since the "addition of inert flash-reducing agents, however, reduces the ballistic power or potential of the powder" (Elements of Ordnance, 1938, p. 13) So I would expect the 3" with the greater weight of powder to use the FNH, whereas the 76mm would use the NH, but the opposite was true.
I suppose the the British weapons, with same projectile but different powder weights and different barrel lengths can also give insight. Obviously, the 17 pdr. projectile weighs more than the US 76.2mm projectiles.
Yes, 16.95 to 17 pounds versus 15.43 pounds. I wonder what propellant powder the British used?
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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 Richard Anderson » 02 Feb 2018 19:28

Yoozername wrote:But getting back to the topic, that is this pseudo-report, it never mentions the issues with the gunpowder and the ammunition being changed even though they include a cutaway that shows the later version of the ammunition. I have mentioned it before and the 3 inch gun ammunition could possibly have taken a bigger charge (cutaways show the void inside). The Soviets even mention this when they tested theirs. But, could the US projectiles withstand greater velocities without breaking up? Especially when striking sloped armor?
The report of the 2d Isigny test also mentions the 76mm could have taken a bigger charge. Meanwhile, I wonder if the incomplete combustion found in using the original "short" primer used in the 76mm cartridge may have contributed to an actual loss of Mv as well as the smoke and flash it produced (ironically from a "flashless" powder)? Anecdotally, performance seemed to improve in late 1944 when the "full-length" primer cartridges began to arrive, but that may have been simply due to better sensing and accuracy.

In terms of the problems with the 3" APC projectile itelf, "As late as 1947, U.S. Navy tests at Dahlgren Proving Grounds found 3” M62 APC split and broke up when impacting 3” homogeneous armor plate at 30°and 60°obliquity at velocities up to 2,900 feet per second. On examination, the projectiles exhibited variable hardness with soft spots at the nose, contributing to the failures. However, Navy 3” Mark 29-2 AP projectiles did not shatter." (from my ms.) You may want to look for J. J. Glancey, Progress Report No. 1 on Development of High Velocity Armor-Piercing Projectiles, (Dahlgren, Va.: U.S. Naval Proving Ground, 1 November 1947), p. i.
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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 » 03 Feb 2018 16:35

Sheath hardening isn´t a wise choice for 3" APCBC-HE projectiles. And the tests confirmed this.

The Mk.29 mod2 also had it´s share of problems:

#4872 --2357fps--30° -not effective (base cracked)
#4873 --3448fps--29° -not effective (base cracked)
#4886 --2740fps--30° -not effective (broke up)
#4888-#4891 --2740fps --30° -not effective (broke up/ split)

Shatter would be a less common experience, though break up occurred as well.

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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 Richard Anderson » 03 Feb 2018 17:25

critical mass wrote:Sheath hardening isn´t a wise choice for 3" APCBC-HE projectiles. And the tests confirmed this.

The Mk.29 mod2 also had it´s share of problems:

#4872 --2357fps--30° -not effective (base cracked)
#4873 --3448fps--29° -not effective (base cracked)
#4886 --2740fps--30° -not effective (broke up)
#4888-#4891 --2740fps --30° -not effective (broke up/ split)

Shatter would be a less common experience, though break up occurred as well.
Was the better solution going with an improved AP as in the 90mm T33 and abandoning the HE bit entirely? Ordnance seemingly hung its hat on HVAP as the "solution" for 76mm...until they abandoned that in the 1950s because it exacerbated barrel wear.
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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 » 04 Feb 2018 16:27

The US did have a APDS program during WWII. It almost made it in before the war ended. The US APCR, unlike some others, were very accurate by most accounts. Did the US APDS get too anal retentive about accuracy or some other parameter? I have no idea. The US had many programs, under many branches of the services, with many scientists, etc. It would have been better served with better organization and focus.

As far as actual use of the APCR, it seemed to be rare even into 1945 with tank battalion commanders saying as much.

Barrel wear, with some war-time commanders saying it should not have been an issue...even accepting barrel life as low as 200 rounds...may have been from the change from 1/40 to 1/32 rifling. Rifling has to be a compromise with velocity. Having a weapon fire a variety of shell types...AP, HE, HEAT, APCR ...needs a rifled barrel that can assure some degree of accuracy for all of them. Especially when having a range of velocities.

All-in-all, the US 3in and 76mm APCR had to do. It was late to the party, the US certainly were aware of the German APCR ammunition very early, and the whole post D-Day invasion experience suffered from the pre-D-Day planning and bureaucracy.

If I were a M10 TD Battalion officer, I would certainly investigate the field expedient of adapting the German 76.2 mm ammunition they produced for the Soviet F-22 guns. I would take the projectile and use the US brass with a full powder charge. This would certainly do a job on a Tiger I or a Panther's turret 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 Richard Anderson » 04 Feb 2018 18:59

Yoozername wrote:The US did have a APDS program during WWII. It almost made it in before the war ended.
NDRC began work on HVAP-DS for various 75mm, 76mm, 90mm, and 105mm rounds concurrently with HVAP in the summer of 1942. The University of New Mexico research team worked on the project through 31 September 1944, but never completely solved the problem of sabot separation. Remington Arms then continued development work on the 76mm and 90mm through a final series of tests ending 16 December 1944. While some of the results were promising, none of the work resulted in a finished design.
The US APCR, unlike some others, were very accurate by most accounts. Did the US APDS get too anal retentive about accuracy or some other parameter? I have no idea. The US had many programs, under many branches of the services, with many scientists, etc. It would have been better served with better organization and focus.
HVAP-DS was inaccurate, regularly failed separation, broke up in the barrel, damaged the barrel, and so on. See J.W. Greig, Work on Sabot-Projectiles by the University of New Mexico Under Contract OEMsr-668 and Supplements, 1942-1944, NDRC Report No. A-428, OSRD Report No. 6499, (Albuquerque, NM: University of New Mexico, 1946).
As far as actual use of the APCR, it seemed to be rare even into 1945 with tank battalion commanders saying as much.

Barrel wear, with some war-time commanders saying it should not have been an issue...even accepting barrel life as low as 200 rounds...may have been from the change from 1/40 to 1/32 rifling. Rifling has to be a compromise with velocity. Having a weapon fire a variety of shell types...AP, HE, HEAT, APCR ...needs a rifled barrel that can assure some degree of accuracy for all of them. Especially when having a range of velocities.

All-in-all, the US 3in and 76mm APCR had to do. It was late to the party, the US certainly were aware of the German APCR ammunition very early, and the whole post D-Day invasion experience suffered from the pre-D-Day planning and bureaucracy.
Pretty much...and add complacency on the part of Ordnance. When called on to produce 76mm HVAP Ordnance did so in a commendably short time, but there was little reason it should not have been available earlier other than the unfounded belief that the 76mm and 90mm APC projectiles were excellent, which thorough testing should have revealed was not true.
If I were a M10 TD Battalion officer, I would certainly investigate the field expedient of adapting the German 76.2 mm ammunition they produced for the Soviet F-22 guns. I would take the projectile and use the US brass with a full powder charge. This would certainly do a job on a Tiger I or a Panther's turret armor.
Given that was almost exactly what George Jarrett and Major Northy did two years earlier in North Africa, it is surprising that did not happen.
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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 » 05 Feb 2018 18:05

Was the better solution going with an improved AP as in the 90mm T33 and abandoning the HE bit entirely? Ordnance seemingly hung its hat on HVAP as the "solution" for 76mm...until they abandoned that in the 1950s because it exacerbated barrel wear.

The 90mm T33 wasn´t that much better, except for the higher expectations. There are projectile acceptance datasets to proove that. The 90mm T33 was generally intact against 220-225BHN (SOFT!) RHA at 0° until ca. 2100fps. However, at 2150fps, against a discriminate 6" plate(265BHN), half of the fourteen T33 shells shattered.
Against 8" (220BHN), at 3232fps, they generally shattered, too.

At 20° and from a large dataset (271 projectile acceptance tests), the 90mm T33 experienced both, intact penetration and shatter againt 5" RHA and
only 2008fps.

At 30° and 4" plate (24 test shots), some shattered, some stayed intact, creating a BL=1939fps
At higher velocity and at higher obliquity, the 90mm T33 APBC either broke up or shattered all time. Therefore, unlike many others, I don´t consider the 90mm T33 APBC a successful anti tank projectile. From the USAPG´s own account, I understand that expectations and performance have a delta in it.

The larger the cal. of the AP, the less triaxial stress i involved in cal/sized penetration against ductile, homogenious armor. Thus delay actuated HE filler worked best with major calibre shells (i.e. naval applications) and worked least well with small calibre AP.

Tank ammunition is somehow between both extremes but make no mistake, creating a service reliable, delay action fuze, filler, projectile & cap combination in an AP projectile was extremely difficult with the technology and skill at hand -if it was supposed to work reliably at low and high obliquity impact, against both, thick or thin plate.

To the best of my knowledge, only the 1942-1945 period Pzgr39 series APCBC-HE ever came close to that, working decently at 0°-40° obliquity at various striking velocities, with some projectile lots beeing satisfyctory even at 50°-60°, (only) if the attacked plate was thin and/or soft (ductile) enough. They recognized the importance of Rc hardness in relation to calibre and fully utilized a sweet spot in hardness (Rc 61.5 for 75mmm, going up for smaller calibres and down for larger calibres).

Soviet low Rc hardness AP broke up even at 0° impact -regularely when attacking their domestic Mz-2 armor, and frequently when attacking german armor, less when attacking very ductile, US armor-, and the HE-filler was, for most accounts, practically wasted in them (safe some few oddities where You encounter very thin plating at low enough velocities).
US medium Rc hardness AP was decent at 0-20° with satisfactory fuze action, but was sensitive to break up and shatter at elevated velocities and obliquities.
British ultra high hardness AP got rid of the HE-filler entirely, providing decent penetration but poor post penetration damage. The solution for the latter was to use higher than advisable Rc hardness in the projectile. This could induce break up at high velocities, which if matched to a specific plate thickness / obliquity combination would obtain both, penetration and projectile fragmentation. A very smart response to the problem but only valid for a narrow set of conditions.

Given the prevalence of medium calibre, medium velocity guns in the US, I´d think that something like HESH would permit the most effect as an anti-tank round against targets ranging from german RHA (1st ductile -brittle transition point) to soviet high hardness armor. It would not be as effective vs US soft RHA (extra ductile), though. Both, german (except mine protective bottom plates) and soviet types of armor are fairly sensitive to shock induced spall damage and shear failure (discing/ plugging), which is exactly the mechanism of failure HESH is best at to exploit. HESH is also rather insensitive to oblique impact effects.

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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 » 05 Feb 2018 19:30

critical mass wrote: Therefore, unlike many others, I don´t consider the 90mm T33 APBC a successful anti tank projectile. From the USAPG´s own account, I understand that expectations and performance have a delta in it.
The Panther tank may have a different opinion. According to Hunnicutts book on the Pershing tank it could penetrate the front of a Panther up to 1100 yards.

Here in 'Armor piercing ammunition for gun, 90mm, M3.' is a firing test of examples of T33 penetrations of a Panther at 500 and 1000 yards.
http://cgsc.contentdm.oclc.org/cdm/ref/ ... ll9/id/161

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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 Richard Anderson » 05 Feb 2018 20:32

Thank you for the detailed reply. Do you have a reference for the APG tests on 90mm T33? Most seem to see it as a golden BB. :D

[edit] Like Armor-Piercing Ammunition for Gun, 90-mm, M3... :D
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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 » 05 Feb 2018 20:38

Mobius, one must be careful not to jump to conclusions based upon too little evidence. The manual it´s not an analytical source discussing the performance envelope. These ordnance pamphlets are for instructive purposes and had to demonstrate that they could defeat armor. From a very limited set of -preslected- trial datas. Notice the absence of perforation failures (creating a qualitative argument, only). That being said, yes, You can have individual T33 ammo which behave better than average, by occurance of delayed break up/ no shatter caused by a rather wide variance of individual projectile qualities -and I don´t disagree with that. However, the majority was worse, and considerably so, as established by post war mass firing trial data, when the significance level and sample size was taken into account and the question was treated quantitatively.

For what´s worth, this is the T33 performance data from USAPG trials:

SI- SHOT INTACT
SB- SHOT suffered BREAK UP
SS- SHOT SHATTERED

source: FINAL REPORT ON AN ANALYTICAL STUDY OF DATA ON ARMOR PENETRATION BY TANK-FIRED, KINETIC ENERGY PROJECTILES. Dated May 1958 (originally classified CONFIDENTIAL).


You might notice that the PANTHER´s glacis was taken as a projectile acceptance specification criterion for the T33 shot. 55°, 85mm (230BHN-263BHN, also similar to PANTHER glacis). The confidence level of where half of the the T33 shot penetrate , from a very large sample (302 shots) is exactly 2683fps coinciding with approx. 450yd firing table range for the 90mm M3. A fraction may be expected to punch a hole (not PERFORATE completely with passage of the projectile or it´s fragments behind the plate not even required, this is ARMY BALLISTIC LIMIT) on this target at larger distances, but equally will also fail to hole the plate from even closer distances...
All T33 projectiles shattered (which is good if a hole was made, as it increases the probability that at least some of the nose pieces get through).
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