Panzer Survival In France

[rexford]

Marders and PzKpfw IVH's are the equal of Panther at close range when it comes to penetrating Shermans and M10's, and lots of tinny panzers may have been needed to stop lots of Shermans. 10 Shermans trying to flank 7 PzKpfw IVH's in defensive positions is more difficult than 10 Shermans against 2 Panthers.

Panzers benefitted from two factors that are little known but significant.

When penetration exceeds effective armor resistance by 5% to 25%, above 25% hits succeed due to momentum. Projectile nose may shatter in 5% to 25% excess penetration range and hit may fail. This is referred to as shatter gap.

Shatter gap occurs because back pressure on nose exceeds allowable limits for lower nose hardnesses used by Americans, British and Soviets.

When penetration equals armor resistance, half of the hits succeed and there will be certain back pressure due to movement of armor material. When penetration reaches 5% above armor resistance, back pressure causes shatter fail which continues until penetration exceeds armor resistance by 25%. Then pieces and fragments start to penetrate again.

75mm APCBC from Sherman will shatter fail against PzKpfw IVH driver plate out to 300m, and then will penetrate. So at close bocage ranges 75mm APCBC from Sherman fails to penetrate 80mm driver plate on StuG and PzKpfw IVH. Some penetrations might occur when nose hardness exceeds shatter gap area, since actual projectile hardnesses in field would vary from design value.

76mm APCBC from M10 and Sherman should penetrate Tiger driver plate at 1000m, however, in France it was reported that hits failed beyond 300 yards. Blame it on shatter gap.

British reported on shatter gap in North Africa, where 2 pounder would penetrate out to a certain range, then would fail over some distance,and then would penetrate again. Or 2 pounder would fail to penetrate at close range and then penetrate further out.

German ammo nose hardness was usually above the shatter gap region.

The other factor favoring panzers is that at close range hits tend to bunch around the aim point, which is often right in the mid section of the upper hull front or glacis. We calculated that range estimation errors and shot-to-shot dispersion would result in the following % of turret hits when M10 fired on the front of a Panther:

100m 2.5% of hits on turret

200m 12.5% of hits on turret

300m 25% of hits on turret

When these close range hits strike the turret they tend to land on the lower areas and avoid the vulnerable mantlet center which is almost vertical.

The 899th Tank Destroyer Bn reported on initial battles with Panther in Normandy, using M10. No penetrations of Panther front armor occurred, a few penetrations occurred through MG port and a few hitson mantlet bounced through hull top armor. This supports the concepts presented in this message.

Unusual phenomena came to the aid of the panzers.

[Guest Michael emrys]

Interesting post. Thanks.

Michael

[Guest Seimerst]

Rexford,

A very good read. I had not heard about shatter gap but it makes sense from your explanation. In close in fights as the Germans, I am going to take more IVs just so I have more barrels firing against the swarming Amis.

[Jarmo]

I want shatter gap!

BTS must immediately code it in.

[Gremlin]

The shattering of solid AP rounds (at velocities around 2600 feet/sec and up) was a major factor in anti-tank ammo development and implementation, leading to ballistic capped and sabot rounds during the war, as well as shaped charges. Check out books by Ian Hogg on these issues. He seems to be the major authority in the English language, at least as regards WWII. Fascinating stuff if you're into the science and engineering side of the equipment.

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War is cruel and you cannot refine it. --Sherman

[rexford]

American and British rounds with armor piercing caps also shattered,and at velocities below 2600 fps.

British 2 pounder AP shattered below 2600 fps.

The published research does not appear to tell the whole story.

[Gremlin]

I believe the armor and round metallurgical composition and properties (e.g., tungsten round or not) would make the difference, afaik.

Where did you get your research, btw? Sounds like interesting reading I'd like to get my hands on. Thanks.

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War is cruel and you cannot refine it. --Sherman

[rexford]

ACHTUNG! Highly technical stuff follows!

We have collected and analyzed firing test and battlefield reports for about 25 years, and have tons of reports from NTIS and other sources that date from WW II. U.S. report on nose hardness effects address shatter gap and penetration increase as nose gets harder.

20mm Test

Projectile Velocity

Nose at

Hardness Complete Penetration*

63.5 Rockwell C 1930 fps

61.5 Rockwell C 2055 fps

56.0 Rockwell C 2185 fps

---------------------------

52.0 Rockwell C 2350 fps (estimated from extrapolated curve, 52 Rockwell C is Soviet ammo hardness from U.S. tests on rounds given to U.S. by Russia during war).

German APCBC and APC nose hardnesses were analyzed by British during war, captured rounds,and results follow:

75mm Pak 40 58.5 Rockwell C

75L70 57.5

88L71 60.0

50 APC 61.5

50 APC 61.5

88L71 61.8

75L48 64.0

------------------

Average = 60.7

U.S. ammo about 56 Rockwell C,a nd British rounds had about the same penetration in tests so we assume effective hardness of British ammo equals U.S.

German rounds averaging 60.7 Rockwell C nose hardness should outpenetrate U.S. ammo by about 7%, based on above data for penetration velocity vs. hardness when data is converted to equivalent thickness using DeMarre equation:

If it takes softer nose 2030 fps to defeat armor when harder nose does it in 1930 fps, harder nose would penetrate 7.5% [(2030/1930)raised to 1.4283 power] more armor at same velocity.

A British table gave 75L70 and 88L56 penetration at 30° versus British plate, which is roughly equivalent to U.S test plate. We converted the figures to 0° penetration using slope effects and T/D ratio and it came to 190mm at 0° and 0m against U.S. quality test plate (3068 fps).

U.S. 75mm APCBC weighs the same as 75L70 APCBC but was shot at 2030 fps. Using DeMarre equation, if Panther 75mm was same hardness and quality as U.S. 75mm it would penetrate 91 x[(3068/2030)raised to 1.4283 power], or 164mm at 0°/0m.

190/164 => German ammo about 15.8% better, so it exceeds prediction from U.S. tests with 20mm ammo, which makes sense since using small ammo to predict large stuff is risky. U.S. compared German 75mm penetratin against Sherman 75mm in a test against same plate at same velocity, German rounds penetrated more armor ("somewhat more armor penetrated").

Germans estimate 168mm/0°/0m penetration for 75L70 APCBC, German test plate about 10% stronger than U.S., for 185mm penetration by 75L70 against U.S. plate.

If 75L48 APCBC were same quality and hardness as U.S. 75mm, it would penetrate 91 x [(2460/2030]raised to 1.4283 power], or 120mm at 0m/0°. Comparing penetration ranges to penetration and armor data, 75L48 penetration should be more like 139mm at point blank.

We have done research on how armor loses effectiveness due to high hardness, casting, flaws and have various graphs that are based on the T/D ratio and other factors. The above analysis is speculative in nature but we try to support estimates and conclusions by cross-checking penetration range reports and other sources.

The research also picked up on some unusual tank, armor and projectile characteristics, such as:

Panther A and D used face-hardened armor on front lower hull and side hull armor (upper and lower), which increased vulnerability to APCBC and APC, although front nose could only be penetrated a short distance by 76mm APCBC. Panther D glacis was face-hardened, based on data we've seen.

T34 used high hardness armor and lost 24% of resistance when hit by 75mm APCBC.

Published data for Soviet AP and APBC is based on face-hardened penetration figures, and may not represent what ammo was capable of. Russian APBC had unbelievable effectiveness against sloped armor due to flat nose.

Pointed noses may bend when sloped armor is hit, and since rounds penetrate sloped armor by going thru hole in downward direction for upward armor slope, noses tend to get in way and retard penetration as they bang against sides of hole. Sloped armor is defeated by driving a plug of armor out of the material, the round then slips through the opening.

122mm AP penetrated Panther mantlet to 700m in combat, 122mm APBC penetrated beyond 2500m due to ballistic cap and superior performance against sloped armor.Valera Potapov has a big article on IS-2 and IS-2m at http://military.virtualave.net/is2_1.html

See British report PENETRATION OF ARMOUR PLATE for more on flat head ammo, how rounds penetrate sloped armor, shatter gap and other topics. The report indicates that shatter gap with 2 pounder AP occurred at less than 2600 fps. Since 76mm APCBC shatter failed against Tiger front beyond 300 yards and was fired at 2600 fps, this suggests that capped rounds do suffer from shatter gap and at velocities below 2600 fps.

Uneven resistance of Panther glacis against repeated hits by same round at same range due to flaws. At Isigny, France, Allied test firing during August 1944 showed that 2 of 3 Panther glacis cracked after defeating hits due to flaws and brittle behavior, follow-up hits near cracks penetrated. U.S. armor prior to October 1943 prone to flaws.

[Jasper]

"Russian APBC had unbelievable effectiveness against sloped armor due to flat nose."

So how come everyone didn't use it I wonder?

[rexford]

U.S. went to HVAP and HEAT after war. APBC was old Russian navy round, and American pride and prejudice during McCarthy years and Red Scare probably wouldn't allow copying a communist ammo type.

Naval rounds at long range strike armor at steep angle, and Russians found way to increase effectiveness. Soviets may have hid true penetration of APBC during war by publishing false penetration data that everyone seemed to accept.

In desert war when M48 met Stalin III, slow rate of fire of 122mm APBC (1.5 rounds per minute) gave M48's time to bracket Stalin with HEAT and hit on third or fourth shot.

First shot long, second short, third and fourth closer and closer. HEAT is slower than other rounds but bracketing improves accuracy.

[illo]

Punt!

[illo]

Bump!!

(where is everyone..i thought this might be interesting)

[Jarmo]

Well this is interesting. But what's there to add to it?

[Ari Maenpaa]

Mensch's recent 'Natter gap'-parody post reminded me about this interesting shatter gap phenomena. For easier reading I quoted Rexford's data about 76mm's shatter gap from other thread:

Originally posted by rexford:

U.S. Navy tests on 76mm APCBC suggest following scenario vs. 76mm at 30° from vertical:

1900 fps impact no penetration

2076 fps impact half penetrate

2134 fps impact about 85% penetrate

2148 fps impact half penetrate

2200 fps impact all fail in shatter

2400 fps impact all fail in shatter

2426 fps impact half penetrate shattered

2544 fps impact all penetrate shattered

Shatter gap is area where round should penetrate but doesn't, from 2200 to 2400 fps.

In general, armor thickness has to be at least 85% of projectile diameter for shatter gap, based on limited test data.

If U.S. 75mm follows typical pattern vs 80mm vertical plate, it would penetrate from 750m to 950m using CM data, and fail inside 750m range. Side angles would change effective ranges.

No wonder if US76mm didn't fulfil the expectations.

Anyway, BTT

Ari

[Dittohead]

I was reading a book on the 2nd AD and some tanker was talking about how he fired 4 rds from 200m at the side of a panther and did no damage. but the 5th one finally penetrated. Must have been shatter gap.

[rexford]

We have now revised our views on shatter gap after looking at Shoeburyness tests. 75mm APCBC did not shatter fail when penetration exceeded resistance by more than 5%. It appears that impact velocity must be at least 2000 fps for rounds to break up, armor thickness must be close to, equal to or greater than projectile diameter, and penetration must exceed resistance by more than 5%.

[Paul Lakowski]

Originally posted by Ari Maenpaa:

Mensch's recent 'Natter gap'-parody post reminded me about this interesting shatter gap phenomena. For easier reading I quoted Rexford's data about 76mm's shatter gap from other thread:

No wonder if US76mm didn't fulfil the expectations.

Anyway, BTT

Ari

One principle reason American ammo did so poorly in WW-II had nothing to do with metalurgy but every thing to do with buraucracy.

They never actually tested against slanted armor . Instead they fired at vertical plates and just assumed the geometrical LOS would tell them how much it would be @ 60°. Thats to say if it penetrated 100mm @ 0° it should penetrate 50mm @ 60°, right?

Well had they tested they'd have found out that for there sharply pointed rounds vertical penetration of 100mm @ 0° would translate into 40mm @ 60°[ 80mm LOS] or even worse 53mm @ 45°[76mm] ...looks like the german idea of leaving sloped glacis at 45-55° made a lot more sence than the Russian idea of 60°!

And if you think thats bad you should see the HVAP figures!