CMFB patch released

[NUTTERNAME]

I recall the M61 75mm basically just had better penetration against face hardened armor. Since most AFV had moved away from FH armor, I wonder what the crews used if given the option of M72 or M61.

The M61 did not do well against sloped armor also. I believe even the US documentation showed this.

I really wonder about these lower hull hits and the vulnerability AFV like Panthers etc. supposedly have. The major factor, that I can guess, is that sloped armor might behave differently if either swept back (like the upper hull) or if swept downward (like the lower hull). At first this may sound irrelevant, but I suspect the dynamic might have to do with the spin orientation. Most weapons have a right hand twist and this might help when attacking back-swept armor, and actually hurt performance when attacking downward swept armor. The main problem is that ricochet is induced better by the downward swept armor.

Also, I do not think most games take into account the descent angle or actual flight orientation that a projectile has when striking these lower hull araes. While small, it would add to the sloping just like obliquity would.

 

[mOBIUS]

I don't include FH values as it isn't used in our games.
There are also a lot of small factors that could change the numbers. Target angle, relative height or tilt. Firers cant can affect targeting as the gun may shoot low. All those things probably are greater than the descent angle.

The descent angle of 76mm M1 M62 at 1200m is about 43'.

 

[NUTTERNAME]

I don't include FH values as it isn't used in our games.
There are also a lot of small factors that could change the numbers. Target angle, relative height or tilt. Firers cant can affect targeting as the gun may shoot low. All those things probably are greater than the descent angle.

The descent angle of 76mm M1 M62 at 1200m is about 43'.

Actually, relative height differential is part of descent angle. It is just the physics engine may not take that into account.

An example from CM is the following:

A sherman 75mm is firing at a jgdpnzr IV/70 that is at a higher elevation. The descent angle is actually a major factor when taking the range and height into account. In simple terms, its somewhat plunging as it 'sees' the target. if you have ever fired a weapon 'uphill', you know what I mean. In fact, the velocity is lower than expected.

Likewise, if you are firing at a target at lower elevation, the lower hull is again being 'seen' as the projectile approaches at a greater 'slope' than the spec, but is also a smaller target. So, it s not only an increase in armor slope, it is actually a smaller target area.

An odd anecdote from CM was just this scenario...that is, a sherman firing at a jagdpanzer that was about 900 meters away and at a higher elevation. The game reported a hit on the jagdpanzer floor plate! This is impossible given the trajectory of the projectile. That is, unless the game models ricochets off the ground.

Artillery ricochet fire (using a delay fuse) is affected by spin. If I recall, at lower translational velocities, high rotational velocities have an influence on the shell actually bouncing off the ground.

 

[NUTTERNAME]

An interesting note is that THE US FIRST ARMY TEST AT ISIGNY: 12-30 JULY, 1944 used M61 for the 75mm exclusively. The 3 in. M10 used M79 and also M62. they concluded that m62 was superior, at least against panthers mantlet.

http://www.freerepublic.com/focus/f-chat/2998207/posts

 

[mOBIUS]

The M79 might have shatter gap issues. In the Yugo tests it penetrated the 90mm rounded T34-85 turret front at 900m. So you might expect it to penetrate the 100mm rounded Panther mantlet at 200m.
[edit]
On page 35 in this test document http://www.dtic.mil/dtic/tr/fulltext/u2/301343.pdf
The 76mm M79 penetrated 4" plate of various BHN strengths (200, 260, 320 BHN) without shattering 'SI'.
When faced with 5" plate it also penetrated 212-263 BHN plate intact.
However, vs. 5" plate of 311 BHN it shattered at 2577 ft/s which is under 50yd.

Other tests 4" @ 30° 207-302BHN penetrated intact and some shattered. So maybe more test shots to the mantlet would result in some penetrations and some shatters.

I found some citation that the Panther mantlet was "while the mantle cast hardness was reported to be 210-245".
So the M79 not penetrating this seems to be at odds with the test data.

 

[NUTTERNAME]

The M79 might have shatter gap issues. In the Yugo tests it penetrated the 90mm rounded T34-85 turret front at 900m. So you might expect it to penetrate the 100mm rounded Panther mantlet at 200m.

Reading the tests pre-D-day (Shoeburyness, UK; 23 May, 1944), and the subsequent 'field shoots' after D-Day, I am basically left with the feeling that too many variables are being 'tested' in a non-scientific manner.

I have also seen the 'Yugo Test' data, but one should know that while the targets are probably representative of WWII objects, the ammunition in many cases was rebuilt and improved. Very little details is known other than what is on the internet.

I WOULD expect the M79 3 inch projectile to penetrate the frontal cast armor of the Panther turret. This includes the mantlet and the turret front armor (both castings BTW). An important test issue is how many rounds were fired. I suspect it was just one to three by each weapon and that in this test, "Firing Tests conducted 12-30 July 1944 by 1st U.S. Army in Normandy" (aka #2), here is the methodology...

(Purpose: To conduct tests to determine the effectiveness of tank and anti-tank weapons in First U.S. Army, against the German Mk V “Panther” and Mk VI “Tiger” tanks.

1a. Firing was conducted on terrain permitting 1500 yards maximum range with zero angle of site. All guns and types of ammunition, suitable for anti-tank purposes, available to First U.S. Army were defeated on targets whose armour plate was slightly burned. Upon determination of critical ranges, all penetrations were proven against the armor plate of a German Mk V “Panther” Tank with armor undamaged and in excellent condition. All firing was conducted normal to the target. No firing was conducted against the German Mk VI “Tiger” Tank as there were none available.

So, it would appear that these critical ranges were somehow surmised (penetration charts, etc.), and then "proven". I don't think the conclusions can be made given the small sampling.

I don't think the following conclusion can be justified...

7) 3-inch Gun, M5, mounted on Motor Carriage, M10

a) APC M62 w/BDF M66A1 will not penetrate front glacis slope plate at 200 yards. Will penetrate gun mantlet at 200 yards and penetrate sides and rear of the ‘Panther’ Tank up to 1500 yards.

b) AP M79 will not penetrate the front slope plate or the mantlet at 200 yards. It holds no advantage over APC M62 ammunition w/BDF M66A1.

http://wargaming.info/1998/us-army-1944-firing-test-no2/#.V1LYfMArLcs

It's very interesting that 90mm M82 ammunition, that had been tested pre-D-day, is not part of this post D-Day test (they used M77 and it is actually one of the best weapons tested).
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.

The recommendations call it out...

2. That upon availability of 90mm APC M82 ammunition in this theater, tests be conducted to determine the effectiveness of this ammunition against the ‘Panther’ Tank.

...But, the M82 clearly had fuse issues in the pre-D-Day test...

 

[mOBIUS]

Per the ballistic limit of the US tests the M79 will penetrate 4" armor in 1500m-1700m depending on BHN. So 90mm rounded at 900m should be in its wheelhouse.

 

[NUTTERNAME]

I suspect that both hellcat and sherman 76mm used M62 APC and not M79 in the M1 weapon (perhaps M79 was a substitute-standard but not actually needed). The M10 and towed ATG used different cartridges than the M1 76mm and seemingly used M79 and M64 since they were tested in the field using both. Sherman 75mm probably used M61 as normal AP especially later in the war.

The 'Third' test U.S. Army Firing Tests conducted August 1944 by 12th U.S. Army Group at Isigny, France, seemed to focus on 75/76mm weapons and ammunition. Also, they are clearly focused on penetrating panther upper and lower hulls. The US 76.2 mm firing M62 ammunition fails to penetrate the lower hull of a Panther at 400 yards.

As stated in the test, the Panther hull armor is actually greater than the 'spec'.

Glacis Plate 85mm (3.35″) at 55º and Nose Plate 65mm (2.56″) at 55º. using U.S. armor basis curve, the verticle equivalent of the glacis plate is 187mm (7.36″) and of the nose plate 139mm (5.47″). Due to the inclination of the ground, the angle with the verticle of the glacis plates on the tanks used in this test were: 57º 34′, 57º 05′, and 56º 53′. The nose plate on one of the tanks tested measured 66.67mm (25/8″).

Wargamers should understand that the correct way to understand this is that the armor thickness is actually 'in spec'. That is, the specification may call out that armor plate delivered is -zero/+10%. That means if a plate is 50mm on a drawing, it can actually be 50-55mm and still will work in the jigs needed to manufacture the tank. Obviously, an armor manufacturer is not going to flirt with the low side of the spec because that would mean that after a tremendous amount of investment in alloying and cross-rolling, etc. They have made scrap.

My understanding is that cast armor is even more variable. i would suggest it is used in such a way that it is not dimensionally critical.

 

[NUTTERNAME]

Per the ballistic limit of the US tests the M79 will penetrate 4" armor in 1500m-1700m depending on BHN. So 90mm rounded at 900m should be in its wheelhouse.

This is the Panther cast Turret front armor without the mantlet. The big giveaway it's a casting is the '106' number. This casting includes the 'rounded 'ears' and would be welded to the side turret armor. This frontal turret area underneath, and to the sides of the mantlet would be vulnerable.

The mantlet may have given superior protection beyond its thickness and casting by the shape itself. Full bore projectiles have trouble getting through the armor due to the strength that a curved surface possesses. I recall debating this with Redford.

View attachment 53600

 

[mOBIUS]

The mantlet may have given superior protection beyond its thickness and casting by the shape itself. Full bore projectiles have trouble getting through the armor due to the strength that a curved surface possesses. I recall debating this with Redford.
View attachment 53600

Correct. It does some normalizing as well. In the Yugo test the 75mm Pzgr 39 penetrates the round 90-94mm Sherman front turret of 230BHN at the same range (1000m) as it does the round 90mm T34/85 front turret of 406-444 BHN.

Other rounds seem to come within 0-250m of similar capability.

Wargamers should understand that the correct way to understand this is that the armor thickness is actually 'in spec'. That is, the specification may call out that armor plate delivered is -zero/+10%. That means if a plate is 50mm on a drawing, it can actually be 50-55mm and still will work in the jigs needed to manufacture the tank. Obviously, an armor manufacturer is not going to flirt with the low side of the spec because that would mean that after a tremendous amount of investment in alloying and cross-rolling, etc. They have made scrap.

My understanding is that cast armor is even more variable. i would suggest it is used in such a way that it is not dimensionally critical.

Variable penetrations, angles, armor thicknesses, flawed, unflawed armor.
Yeah, who says that there isn't dice rolling in armor and penetration modelling?

I think the solid shot M72 and the M79 came out before the APHE rounds. They were replaced as production ramped up.

I put together two of my graphs on the 76mm M1
http://www.panzer-war.com/Images/76mmM1M79vsM62.jpg

 

[NUTTERNAME]

Correct.

I put together two of my graphs on the 76mm M1
http://www.panzer-war.com/Images/76mmM1M79vsM62.jpg

How do your graphs compare to the 3rd shoot data as far as M62 76mm tests against panther lower frontal hull armor?

400 meters
76mm
APC
Nose #2
4 fired
3 hit
one miss
1. Two rds failed to penetrate nose.
2. One rd penetrated through old hole; not a fair hit.

 

[mOBIUS]

If the glacis is at 57° then the lower hull ought to be at 53°. 65mm @ 53° is ~108mm LOS. My graphs show 105mm penetration at 366m.
So there is less than a 50/50 chance of penetration.
(Though my normalizing process probably as a +/- 3-4% error in it.)

 

[NUTTERNAME]

If the glacis is at 57° then the lower hull ought to be at 53°. 65mm @ 53° is ~108mm LOS. My graphs show 105mm penetration at 366m.
So there is less than a 50/50 chance of penetration.
(Though my normalizing process probably as a +/- 3-4% error in it.)

Do you think M79 would have faired better in the test?

The test states...

a. The above ammunitions were fired at the front plate of three Panther tanks. The general characteristics of the frontal armour are: Glacis Plate 85mm (3.35″) at 55º and Nose Plate 65mm (2.56″) at 55º. using U.S. armor basis curve, the verticle equivalent of the glacis plate is 187mm (7.36″) and of the nose plate 139mm (5.47″). Due to the inclination of the ground, the angle with the verticle of the glacis plates on the tanks used in this test were: 57º 34′, 57º 05′, and 56º 53′. The nose plate on one of the tanks tested measured 66.67mm (25/8″).

So, the M62 would have no chance if the nose plate was ~139mm. The M79 would need to fire point blank and even depress its gun!

If the jgdpanzer IV/70 had a nose plate at 53mm (for the sake of argument) and it compared in quality to the Panther, given the same angle, it would be 113mm or so. That would be much less than your initial estimate as far as range? Maybe vulnerable to M79 at 500m?

 

[mOBIUS]

Do you think M79 would have faired better in the test?

I don't think so. I don't have any penetration curves for the M79 except 0 and 30°.
I do have firing curves for the 75mm M72 and at 55° with a MV=2543f/s. In comparison to penetration at 1000 yds @55° it is only 44.7% of that @ 0 degrees. So that loss of penetration of the M79 even at point blank on normalized data this would not penetrate 65mm@55°. On 237BHN armor it would penetrate at about 500yds.

OTOH, look at the Yugo tests. The M79 penetrates 46mm @60° at 1100m where using the 44.7% number says it should only penetrate 41mm.

So, the M62 would have no chance if the nose plate was ~139mm. The M79 would need to fire point blank and even depress its gun!

You mean equivalent armor? Per TM9 1907 The M62 would penetrate 2.25" (57mm)@55°at 400yds.
That is 237BHN armor. There is a small chance of penetration.
(The 55° degree curve lines are dashed so may not be the result of tests and more or less theoretical.)

I ran the chance to penetrate 65mm@55° vs 3" APHE in Nathan Okun M79AP program and it can be penetrated at 400yds with certain quality armors and will not with other better quality armor.

 

[NUTTERNAME]

You mean equivalent armor? Per TM9 1907 The M62 would penetrate 2.25" (57mm)@55°at 400yds.
That is 237BHN armor. There is a small chance of penetration.
(The 55° degree curve lines are dashed so may not be the result of tests and more or less theoretical.)

I ran the chance to penetrate 65mm@55° vs 3" APHE in Nathan Okun M79AP program and it can be penetrated at 400yds with certain quality armors and will not with other better quality armor.

So, in the case of the Jgdpanzer IV/70 lower hull, you still believe this?

76mmM1 M62 upper front hull 0m
76mmM1 M62 lower front hull 1350m
76mmM1 M62 super@60mm 900m
76mmM1 M62 super @80mm 0

 

[mOBIUS]

I'm looking for anecdotal accounts of penetrations of the front of a Panther. AFV-G2 has an account of the 'belly' of a Panther penetrated from 150yds by a 3 inch APCBDF round. I don't know what that is.

 

[NUTTERNAME]

APCBDF=armor piercing capped base detonating fuse? 76.2 mm M10 perhaps. M62 ammo. I believe the first encounters in Normandy with US forces had Panther's getting knocked out at very close ranges.

 

[NUTTERNAME]

Here is a roughly done comparison of Jgdpzr IV and Panther. The third test is also an accuracy test as well as penetration shoot. I sort of chuckled in that they said it was difficult to target the lower hull so they counted the upper and lower hull together to score a 'hit'. Makes sense. Want better accuracy? Increase the target size!

The 76mm M62 actually had a miss when trying to hit the 'nose' or lower hull. At 200 yards. A known distance under test conditions. perhaps anecdotal, but it is what it is.

Note that the height on the jgdpnz IV lower hull armor is even smaller than the panthers...

View attachment 53631

 

[NUTTERNAME]

An interesting test shoot was the Soviet tests of Elephant TDs captured after Kursk. They tested sherman 75mm using both M72 and M61 ammunition. M72 failed yet M61 made it through. Perhaps it was face hardened armor? I will have to search to see what the range was.

Edit: It was the side superstructure armor.

 

[mOBIUS]

So, in the case of the Jgdpanzer IV/70 lower hull, you still believe this?
76mmM1 M62 lower front hull 1350m

By the TM9 1907 it could be 1500m-1600m. An average of various M62 data sets from US and British sources gives the 1350m. So somewhere in there.