Content deleted Content added
Line 255:
:Aberdeen's documents show something different. Instead of pasting dubious all over did you read their report?[[User:Tirronan|Tirronan]] ([[User talk:Tirronan|talk]]) 04:35, 24 August 2021 (UTC)
Situations like Captain Farmer’s created a scramble to obtain upgraded 76-mm tanks. Some
started to make their way into service by September, but they were still relatively scarce with only
250 of the 1,913 tanks in the 12th Army Group equipped with 76-mm guns (ref. 14). The Tank
Destroyers were the only American vehicles equipped to defeat the German armor while upgraded
Shermans slowly trickled in. They fared better but still were not as successful as anticipated. The
only way the Panther could be defeated from the front was to deflect a shot off of the mantlet
downward onto the armor above the driver’s head (ref. 10). This was the fabled “lucky shot,” and the
odds of achieving this effect are extremely unfavorable.
It seems inconceivable that a 75-mm projectile would fail to penetrate a target at point blank
range. The picture makes sense when taking a look at the physics behind armor penetration. The
following formula is the Lambert-Zukas formula for deriving the limit velocity (𝑉𝑙
), commonly referred
to as the V50 (ref. 15).
𝑉𝑙 = (
𝐿
𝑑𝑝𝑟𝑜𝑗)
.15
∗ 𝛼 ∗ √(
𝑑𝑝𝑟𝑜𝑗3
𝑚𝑎𝑠𝑠𝑝𝑟𝑜𝑗) ∗ [[(
𝑡
𝑑𝑝𝑟𝑜𝑗) ∗ sec(𝜃)
.75] + 𝑒
[−(
𝑡
𝑑𝑝𝑟𝑜𝑗)∗sec(𝜃)
.75]
− 1] (1)
𝑉𝑙 𝐿𝑖𝑚𝑖𝑡 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑜𝑟 𝑉50
𝑡 𝐴𝑟𝑚𝑜𝑟 𝑝𝑙𝑎𝑡𝑒 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠
𝜃 𝑆𝑙𝑜𝑝𝑒 𝑜𝑓 𝑎𝑟𝑚𝑜𝑟
𝐿 𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓𝑝𝑒𝑛𝑒𝑡𝑟𝑎𝑡𝑜𝑟
𝑚𝑎𝑠𝑠𝑝𝑟𝑜𝑗 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑝𝑒𝑛𝑒𝑡𝑟𝑎𝑡𝑜𝑟
𝑑𝑝𝑟𝑜𝑗 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑜𝑓 𝑝𝑒𝑛𝑒𝑡𝑟𝑎𝑡𝑜𝑟
𝛼 = 4000 𝑅𝐻𝐴 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
The 𝑉𝑙
is the velocity that penetration occurs 50% of the time for a specific combination of a
given projectile against a specific target thickness and obliquity angle. A striking velocity below this
𝑉𝑙 or V50 can be considered the point the projectile will not penetrate the target.
The TM 9-1907 lacks any data regarding the Panther, but the Lambert-Zukas 𝑉𝑙 calculation
for the M61 75-mm APC against the frontal hull armor of the Panther is calculated as approximately
3700 fps. The front turret does not fare much better at 3200 fps. This is well over the 2030-fps
muzzle velocity of the 75-mm gun; failure at point blank is a given.
The M10 Tank Destroyer crews discovered in July 1944 that the 3-in. APC shell bounced off
of the front glacis plate of the Panther tank at all ranges (ref. 16). The M62A1 was also the primary
anti-tank round for the 76-mm M1 Guns, which proved unfortunate for the M18 Tank Destroyer
crews. The inability of the 3 in. and 76-mm to penetrate the frontal armor of the Panther sent a
shockwave through allied command.
The first appearance in technical data of the top assembly for the 76-mm HVAP-T round was
dated January 31, 1945, as the T40E20 (75-1-220), though its individual components are accounted
for earlier. The shot, HVAP-T, 76-mm or 3 in., M93 metal parts assembly (75-2-361) was official and
approved November 11, 1944. The initial limited fielding in September 1944 carried the T40
designation since the 76-mm HVAP-T round would be designated the M93 only after February 1,
1945. Figure 5 shows an exploded view of the M93 HVAP-T.
Figure 5
M93 HVAP-T exploded view
The T40E20 (M93) projectile, or “Shot,” consisted of a steel base, aluminum body, tungsten
carbide core, nose, windshield, and bourrelet ring. The tungsten carbide core was assembled to the
cylindrical opening through the center of the aluminum body. The aluminum nose threads into the
mouth of the body, covering the nose end of the tungsten carbide penetrator and holding it in place.
The steel base assembles onto the back end of the body, preventing the core from slipping out of the
body rearward.
The bourrelet ring rests in a recess near the forward end of the body, positioned flush with
the circumference of the body. The windshield was threaded onto the forward end of the body, in
front of the bourrelet band. This process encapsulates the nose and core and holds the band in
place. A tracer in the base of the projectile, ignited by the propellant combustion product, reduces
drag. In a similar fashion as the M62A1, this “Shot” assembly uses the M26 case, loaded with 3.9 lb
UNCLASSIFIED
Approved for public release; distribution is unlimited.
UNCLASSIFIED
10
of M2 powder and an M28A2 percussion primer. The total weight of the 76-mm HVAP-T round was
approximately 18.91 lb with an as-fired weight of the projectile of 9.4 lb.
BALLISTICS MODELING AND CALCULATIONS
Velocity Degradation versus Range
The first method that was considered for the expected degradation of velocity from muzzle
exit over a given range is via hand calculation. This can be represented as a function of the muzzle
velocity, or initial velocity (Vo), and the physical properties of the projectile and air.
Following this reasoning, the velocity at a given horizontal range (x) can be calculated via the
following simplified formula (linear velocity decay formula):
𝑉𝑋 = 𝑉0 − (𝑘2 ∗ 𝑥) (2)
The Constant k2 is derived via the interaction of the projectile cross section and mass with
the surrounding air (ref. 15). This constant was chosen because the velocity of the projectile is
expected to be 0.8M <Vx< 2.5M for much of its effective range.
This is likely a better approximation for the M62A1 APC since its muzzle velocity is in the
Mach 2.3 range. The HVAP-T is also within this Mach number range over much of its trajectory, but
with a muzzle velocity of 3400 fps, the close ranges exceed Mach 2.5. This introduces error into the
assumed linear velocity decay. The validity of this method is also suspect at longer ranges when the
striking velocity drops below Mach 0.8. The effect of Mach number/K constant after evaluating just k2
first will be examined as well as the shift in striking velocity decay when accounting for the subsonic
and above Mach 2.5 portions of the trajectory.
𝑘2 = [
(𝜌∗𝑆)
(2∗𝑚𝑎𝑠𝑠)
] ∗ 𝐾2 ∗ 𝑎 (3)
𝑆 = 𝐶𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑝𝑟𝑜𝑗𝑒𝑐𝑡𝑖𝑙𝑒
𝐷𝑒𝑟𝑖𝑣𝑒𝑑 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝐾2 = 0.841
𝐶𝑑 = 𝐷𝑟𝑎𝑔 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝐾2 = 𝐶𝑑 ∗ 𝑀𝑀 = 𝑀𝑎𝑐ℎ 𝑛𝑢𝑚𝑏𝑒𝑟
𝑆𝑝𝑒𝑒𝑑 𝑜𝑓 𝑠𝑜𝑢𝑛𝑑 𝑖𝑛 𝑎𝑖𝑟 𝑎 = 1120 𝑓𝑝𝑠
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑃𝑟𝑜𝑗𝑒𝑐𝑡𝑖𝑙𝑒 𝑚𝑎𝑠𝑠 = 11.09 𝑙𝑏 for (M62A1 APC)
𝐴𝑖𝑟 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝜌 = 0.0751 𝑙𝑏/𝑓𝑡3
Attempting to find the velocity at a range of 500 yd, 1,500 ft is inserted for x in the equation.
Given that the muzzle velocity for the M62A1 is 2600 fps, the expected velocity at 500 yd is
calculated to be 2433 fps. In order to determine the rate of degradation, a series of ranges are
evaluated similarly.
The predicted velocity degradation over range can now be predicted using the previous
equation. Given the velocity curves for each shell, it is determined how each should retain its
velocity. Figure 8 contains the two 76-mm (M62A1 and M93) and one 75-mm (M61) anti-tank shells.
This plot indicates velocity from muzzle exit to a range of 5,000 yd. The HVAP-T is expected to retain
UNCLASSIFIED
Approved for public release; distribution is unlimited.
UNCLASSIFIED
14
a higher velocity over the same given range as its counterparts, except for over a range of 4,200 m.
This is not surprising given that it starts out with a much higher muzzle velocity. What is surprising is
that the M61 75-mm APC seems to retain its velocity on par with the M62A1 76-mm APC. The lower
performance of the 75-mm is likely related to its lower muzzle velocity rather than an issue with the
projectile design. The “Y intercept” has also been adjusted to 3800 fps for the fourth case, which is
the M93 HVAP-T in an uncut original longer barrel 76-mm gun.
The bow is the thickest part of the Pz IV hull. The 76-mm M62A1 APC with a muzzle velocity
of 2600 fps would have no issue defeating the “E” variant at typical combat ranges in the ETO, which
were within 890 yd (ref. 7). The turret is more stubborn but is still vulnerable. These results support
the reasonable conclusion that the 76-mm gun with the M62A1 APC would have little difficulty
defeating earlier model German Panzers. However, by the time the M1A2 76-mm arrived in the ETO
in the summer of 1944, the Pz IV received several upgrades in armor and armament.
The Germans produced over 3,500 of the Ausführung (Ausf.) H by July 1944 and was the
most numerous tank in the Panzer corps during this timeframe (ref. 2). Since the “H” variant was the
most numerous tank in the German war machine, it was the probable adversary even after the
introduction of the Panther. The armor thickness increased for the bow and side turret over the
course of upgrading. Skirt armor strengthened the side of the hull and turret but tended to break off
under combat conditions. Table 4 shows the Lambert-Zukas comparison for the M62A1 APC versus
Pz IV H.
Table 4
Lambert-Zukas V50 - M62A1 APC versus Pz IV H
The effect of the armor upgrade is evident. The V50 is more than doubled for the side and rear
strike on the turret, which is the result of add-on armor applied around the turret. The front hull
increased to near muzzle velocity for the APC. This was a serious issue since the 76-mm armed with
the APC would be marginal at best to penetrate the frontal hull armor of the “H” and was reduced
significantly relative to the “E” model on a flank attack as well.
76mm Front Hull Front Turret Side Hull Side Turret Front Hull Front Turret Side Hull Side Turret
Lambert-Zukas 2176.41 2667.71 1803.37 1008.87 4176.45 3687.88 2327.01 2075.23
Thompson 1370.41 1681.01 1106.62 702.04 5060.99 2520.26 1338.22 1385.30
BAL 66 1873.00 2244.00 1582.00 987.00 3861.00 3067.00 2528.00 1818.57
M
LAMBERT - ZUKAS (ZERO DEGREE FACING)
Gun Caliber 75mm 76mm 76mm 76mm
Ammunition M61 APC M62A1 APC M93 HVAP-T
M93 HVAP-T
(Long Barrel)
Muzzle Velocity (fps) 2030 2600 3400 3800
Front Hull 725.00 3078.00 2173.76 3020.75
Front Turret 0.00 1712.00 1239.25 1992.35
Side Hull 1750.00 4170.00 2960.65 3908.00
Side Turret 4050.00 6722.50 5002.00 6400.00
Rear Hull 4050.00 6722.50 5002.00 6400.00
Rear Turret 4050.00 6722.50 5002.00 6400.00
Front Hull 0.00 50.00 163.15 832.00
Front Turret 0.00 1712.00 1239.25 1992.35
Side Hull 1238.00 3622.00 2562.50 3456.39
Side Turret 785.00 3140.00 2217.15 3069.25
Rear Hull 4050.00 6722.50 5001.90 6400.00
Rear Turret 785.00 3140.00 2217.15 3069.25
Front Hull 0.00 0.00 0.00 0.00
Front Turret 0.00 0.00 0.00 249.00
Side Hull 320.00 2653.00 1876.50 2691.00
Side Turret 1000.00 3370.00 2379.63 3250.00
Rear Hull 1385.00 3777.50 2673.95 3582.40
Rear Turret 1000.00 3370.00 2397.63 3
The 75-mm gun is ineffective at point blank even against the front turret of the Pz IV E and is
only effective at close ranges against the side hull armor of the Panther. Captain Farmer’s
predicament recounted previously in this report becomes painfully clear.
The introduction of the 76-mm M1 Gun and M62A1 APC shows a marked performance
increase against the Pz IV E in respect to its 75-mm counterpart. The effective range increases from
725 yd to over 3,000 yd against the front hull and from point blank failure against the front turret to
1,700 yd for the 76-mm APC. The velocity drop-off is more drastic with the HVAP-T than APC,
evidenced by the nearly 1,000-fps difference in V50 between the two against the frontal armor and a
drop-off from 1,712 to 1239 yd, which is in the effective range in table 6. Given most tank
engagements in the ETO were within 890 yd, this wasn’t a horrible drop-off in performance (ref. 7).
This is not the entire picture of the close-in performance increase with the HVAP-T, which is evident
when evaluating the up-armored Pz IV H.
The benefit of the HVAP-T round is evidenced in the close range fight. Penetration of the
frontal armor of the Pz IV H is increased from 50 yd with the M62A1 APC to 163 yd with the HVAP-T
round (table 6). The detrimental effect Pz IV H upgrade on 76-mm APC performance is evident. The
front armor was increased and is nearly invulnerable to the M62A1 APC shot. Side hull and turret
armor upgrades cut the effective range significantly in flank attack. The performance improvement
with the HVAP-T is evident at close range fight. A gun crew needed to know this distinction between
their APC and HVAP-T performance to effectively engage the enemy based on range to target.
Ramping the M93 HVAP-T muzzle velocity up to 3800 fps to account for the lost cannon
length yields some interesting results. The front hull of the Pz IV H would be vulnerable out to
832 yd, covering the full range of tank engagements in the ETO. The Panther is vulnerable at
249 yd, which is improved from the point blank failure. The Hellcat or Sherman armed with the
unaltered 76-mm gun would have had a much better chance of defeating the front hull armor of the
Panther. Cutting the muzzle length to save weight while reducing velocity on the muzzle exit was a
costly mistake that hampered the Tank Destroyer’s primary mission, which was destroying German
Panzers.
The British had no doctrine imposed limits dictating cannon weight. They incorporated their
own 76-mm gun, dubbed the 17 pounder. Three times the amount of propellant coupled with a
longer barrel than the US M1 76-mm meant that the muzzle velocity obtained by their Sherman tank
mounted weapon was significantly higher than their American counterparts. The armor piercing
discarding sabot (APDS) round for the 17 pounder had a muzzle velocity of 3950 fps. Without
conducting an analysis for the 17-pounder ammunition, a “what if” scenario can be conducted with
the M93 HVAP-T design. Ramping up the M93 to the 3950 fps results in a weapon capable of
defeating all German armor at ranges well beyond the average tank engagement in the ETO. Given
the 17 pounder was mounted on the same Sherman tank chassis as the M1 76-mm, this is an
entirely plausible and effective solution to the Panzer upgrade problem.
I could go on but I think I have made my point. I did some serious research to get the data. If you care to refute it then bring your proof and we can have a discussion about it. Otherwise please remove all references to dubious. [[User:Tirronan|Tirronan]] ([[User talk:Tirronan|talk]]) 04:51, 24 August 2021 (UTC)
| |||