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US Armor

Discussion in 'Armor and Armored Fighting Vehicles' started by GunSlinger86, May 23, 2016.

  1. RichTO90

    RichTO90 Well-Known Member

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    Um, it was quite a bit more complex than that. There is actually little hard evidence for "resentment" until late in 1944. It was actually October before the 4th Armored Division was persuaded to accept any Medium Tank M4 with a 76mm gun.

    The "problem" with the 76mm wasn't really a single problem with the gun or in testing...it was multiple problems. The standard projectile, the 76mm APC M62 was produced with a large cavity for the burster, because everyone assumed that it was the behind-armor effect of the HE bursting that would do the most damage. However, there were two problems with that. For one, the larger cavity weakened the projectile, causing it to stress shatter when striking at high projectile diameter to armor thickness ratios. And then, even when it didn't fail, the BD fuse (common in all the US APC rounds) tended to go off before penetration was completed, destroying the projectile and preventing penetration. However, when tested at Aberdeen they weren't testing for behind-armor effects, so the cavity was inert filled, which improved the results. The problem was exacerbated by the simple fact they assumed the Germans would be using armor similar to our own and BRL did not have samples to test to destruction until late 1943 in the case of the Tiger, early 1944 in the case of a late-model Panzer IV, and late October 1944 in the case of the Panther, which was far too late since the 76mm gun development was completed in early 1942. On top of that, it wasn't until June 1944 that it was realized the hardness specifications for the American projectiles was insufficient as well, which meant that the solid AP projectiles were also deforming and shattering when striking the German armor, even though after the initial problems found with the APC rounds had led to the assumption relying on the simpler AP shot would solve the problem. The solution was re-heat treated AP shot, the M77 in the 90mm, which became the T33, while in the 76mm work on perfecting the HVAP continued.

    On top of that, the 76mm had major issues with flash and blast obscuring observation of the fall of shot. The flash problem was solved when it was found that it was caused by failure to completely combust the propellant in the cartridge...the solution was a longer ignition primer. Blast could be solved by a muzzle brake, but it was considered NIH - and too "German" - so was delayed in deployment.

    Of course, the worst problem was the conservatism of Ordnance. The flash problem could have been solved from the get go with flash suppressing chemical additives, but they were considered to cause excessive wear in the tube so were rejected, since Ordnance liked to achieve 1,000+ round lifetimes in its barrels, which hardly helped when the tank it was fitted to only fired 200 rounds before it was knocked out. On top of that, despite advice to increase the propellant load and thus increase chamber pressure and Mv (as did the Germans in the Pak/KwK/StK 40 and KwK 42 and the British in the 17-pdr) in the 3" and 76mm, Ordnance refused because of concerns with safety issues. Fundamentally, there was nothing mysterious about the 17-pdr that made it a better 3" gun than the American 3" gun, since, despite the nomenclature, the 17-pdr, 77mm, 76mm, and 3" guns were all very similar pieces.
     
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  2. DaveOB

    DaveOB Member

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    You mean all they had to do was increase the propellant load and they could have gotten more muzzle velocity with no modification to the gun whatsoever?
     
  3. Pacifist

    Pacifist Active Member

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    Increasing the propellant load would require a longer shell casing which would require a modification of the gun. Unless you're talking about using a different propellant.
     
  4. OpanaPointer

    OpanaPointer I Point at Opana Staff Member WW2|ORG Editor

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    Any candidates for that?
     
  5. RichTO90

    RichTO90 Well-Known Member

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    It already did. The 76mm rounds, the M42A1 HE, M62A1 APC, and M79 AP, all used a propellant load of 3.62 pounds of FNH powder to ballistically match the 3" projectiles with its propellant loads of 4.62 pounds of NH powder. There was room though in the M26 cartridge case for the 76mm for additional propellant, while the Mk II M2 cartridge case for the 3" also had room for more propellant or could have been loaded with the more energetic FNH powder. Either would have increased chamber pressure and Mv.

    After the second Isigny test it was recommended that American HVAP projectiles fired with 17-pdr cartridges would be a perfect combination.
     
  6. DaveOB

    DaveOB Member

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    Unbelievable
     
  7. RichTO90

    RichTO90 Well-Known Member

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    What is?
     
  8. RichTO90

    RichTO90 Well-Known Member

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    Sorry, major clarification above.
     
  9. DaveOB

    DaveOB Member

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    I find it unbelievable that they could have increased the MV of the 76mm gun and didn't do it.
     
  10. RichTO90

    RichTO90 Well-Known Member

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    Increasing Mv would decrease the service life of the piece and decrease the safety margin for the crew in the event of a malfunction. That was the rationale by Ordnance at least and they stuck to it. Please don't tell me you find it unbelievable the U.S. Army Ordnance Department was that conservative in outlook? They are the same people who delayed acceptance of breechloaders and magazine rifles because they would encourage soldiers to waste ammunition, then over 100 years later insisted on removing the full auto capability of the basic infantry rifle for the same reason.

    Anyway, it would not have done any good to do so since it was a combination of problems. Increasing the Mv without improving the projectile quality would have resulted in fewer penetrations, not more, since it would have increased the tendency for it to shatter. I think by August 1944 that realization was sinking in, which is why the Ordnance officers at Isigny recommended the T4 HVAP projectile on the 17-pdr cartridge. Of course, they were also likely unaware that the HVAP projectile would be prone to ricochet off highly sloped armored surfaces.
     
  11. DaveOB

    DaveOB Member

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    Would the combination of higher hardness, normalizing, full calibre projectiles and maximum propellant loads in the casings have resulted in them being able to penetrate the Panthers front glacis at reasonable combat ranges?
     
  12. RichTO90

    RichTO90 Well-Known Member

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    Indeed. Postwar tests of 90mm AP T33 resulted in consistent complete penetrations of actual Panthers at most ranges. IIRC. in one test at 1,000 yards the round penetrated the glacis, traversed the crew compartment, went through the Maybach, and exited the rear plate with sufficient velocity to carry it some hundreds of yards downrange.

    From another discussion at TankNet, my friend Ken Estes (Marine armor historian par excellance) mentioned Mike Baily's findings 23 years ago in Faint Praise, where he highlighted the mendacious nature of the postwar Ordnance habit of blaming others for their own technical failings.

    My reply was:

    The more I dig, the more I realize Mike got it almost exactly correct years ago. At the most he may have missed the second piece of evidence damning Ordnance, which was that ever since Jarrett swapped out German projectiles onto American cartridges, Ordnance was aware the German projectiles were superior. As early as 5 June 1943 after testing the German 7.5cm APC and APCBC from the KwK 37 they found it:

    "...superior to the U.S. 75min, M61 APC projectile in penetrating 3-lnch rolled homogeneous armor at a 20° obliquity, but was inferior to the same U.S. projectile in penetrating 3-lnch face hardened armor at a 20° obliquity. The fuze functioning of the German projectile was very regular. As the obliquity of an arrangement of 1-inch face hardened over 2-inch homogeneous armor was Increased, the relative effectiveness of the German projectile over the U.S. M61 APC projectile Increased. The projectile was defeated at velocities up to 1944 f/s by spaced armor arrangement 01 1-inch face hardened plate 10 inches in front of 1-3/4-inch face hardened plate at 30°."

    A later report of the same series of tests of German projectiles on 18 April 1945 (sometimes erroneously dated as "1943") compared German 7.5cm and 8.8cm APC and AP rounds versus US 90mm M82 APC, M77 AP, T33 AP, and 75mm M61 APC and found:

    "The German projectiles had better penetration characteristics against homogeneous armor plate than the American projectiles and demonstrated less tendency to shatter when fired against homogeneous armor plate at high velocities. It was recommended that the design features, hardness pattern, and composition of the German projectiles be studied for the purpose of improving American armor piercing ammunition."

    The only US projectile found comparable to the German rounds was the T33.

    That was two years after the initial report. In the interval, no effort was made to improve the quality of 75mm, 76mm, and 90mm APC and AP rounds, except for the frantic effort to produce the 76mm T4 and then the 90mm T33 (which may not have seen any field service). No effort was made to improve the design of the APC rounds by reducing the size of the HE cavity and burster. No effort was made to improve the hardness specifications and production of the APC or AP rounds.

    However, ordnance managed to escape censure by shifting the blame to McNair, who was conveniently dead and so couldn't reply. Somehow, it was his "obstructionism" and "poor doctrinal choices", which resulted in the technical failures of Ordnance. And yet people still eat up this baseless tripe and spew it forth ad infinitum. [​IMG]
     
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  13. DaveOB

    DaveOB Member

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    Frowny face indeed!
     
  14. USMCPrice

    USMCPrice Idiot at Large

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    There were other reasons for this particular change in addition to the one you mentioned. It was the correct decision.
     
  15. DaveOB

    DaveOB Member

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    Did these same problems affect the 3"guns on the m-10 as well?
     
  16. RichTO90

    RichTO90 Well-Known Member

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    Dammit Price, I was on a roll. I felt like Bluto. :)
     
  17. Terry D

    Terry D Well-Known Member

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    I'll say. A very, very informative comment which throws a lot of new light and tells me things I didn't know. I knew the 76mm gun had problems and that the testing in the States was done wrong, but I never realized before how much of the fault lay with the ammunition.

    One question, though. The British got some 76mm M4s and of course guns and ammo for same. Do you know if their ordnance people detected the problem?
     
  18. GunSlinger86

    GunSlinger86 Well-Known Member

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    Could we have developed a higher velocity 75mm gun similar to the Panther's 75mm gun? Could the turret have remained the same if they kept the gun 75mm, or since higher velocity meant longer barrel and more weight, would the turret have to be changed anyway?
     
  19. RichTO90

    RichTO90 Well-Known Member

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    The Lend-Lease 76mm-armed M4 supplied to the British were all delivered in 1945 IIRC and were allocated to the Poles. By that time the problems were well known.
     
  20. RichTO90

    RichTO90 Well-Known Member

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    We did. It was the 76mm Gun M32 as installed on the Light Tank T37 (M41), which began development in 1947.

    No, the standard 75mm turrets, both the early D50878 and late D78461 types, had issues accepting guns larger than the 75mm M3 Tank Gun. That is why the British welded an armor box at the rear of the turret to accommodate the tank radio. The 76mm D82081 turret could probably have been adapted to a larger gun, but the other issue is the size of the rounds and stowing and working them within the confines of the turret.
     

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