Jump to content

Penetration Probability and Effective Ranges

Recommended Posts

The World War II penetration data figures presented in the CM games appear to represent the 50% success thickness that can be defeated. If a gun with 82mm penetration hits an 82mm plate flat on, half the hits get completely through and half don't.

The 50% success criteria averages the highest velocity that results in a failure with the lowest success velocity.

The penetration probability curve is a bell shaped normal distribution, and actual "standard deviations" for the curve against good armor range from 4% during U.S. trials with 37mm APCBC to 7% for Russian 76.2mm APBC ammo. Firing tests against Tiger resulted in a "standard deviation" of 5.65%.

The "standard deviation" indicates the spread of the curve, where 68% of the results are within one "standard deviation" (plus or minus) from average.

If half the hits succeed when the penetration equals the armor effective resistance (after quality multipliers and slope effects), then the following table applies:

penetration equals armor resistance, 50% success

penetration -0.5 std deviations less than resistance, 31% success

penetration -1 std deviations less, 16% success

penetration -1.5 std deviations less, 7% success

penetration -2 std deviations less, 2% success

penetration -2.5 std deviations less, 0.6% success

penetration -3 std deviations less, 0.1%

penetration 0.5 std deviations over resistance, 69% success

penetration 1 std deviation over resistance, 84% success

penetration 1.5 std deviations over, 93% success

penetration 2 std deviations over, 98% success

penetration 2.5 std deviations over, 99.4% success

penetration 3 std deviations over, 99.9% success

Actual firing tests against the Tiger side armor by the Americans, British and Russians show an average resistance of 84.5mm with a standard deviation of 5.65%. The 84.5mm takes into account thickness variations above the 80mm design spec and ballistic advantages.

If the Sherman 75mm hits the Tiger side armor at 750m range with APCBC and no side angle, the penetration is 77mm and the armor resistance is 84.5mm. The penetration is 8.88% less than the resistance.

With a standard deviation of 5.65%, the Sherman penetration is 8.88/5.65 or 1.57 standard deviations below the resistance. The penetration probability works out to 5.8%.

Reports on the combat where Michael Wittmann's Tiger was knocked out suggest that Sherman 75mm APCBC rounds were bouncing harmlessly off the Tiger side armor at 700 to 800 yards, which could be a function of inadequate penetration at range, side angles to the shots and "unlucky rolls".

If the standard deviation for the 750m hit on the Tiger side armor was 4% or 7%, the corresponding penetration probabilities would be 1.3% and 10.2%.

Poor or flawed armor not only reduces the effective resistance of armor, but the standard deviation appears to be about 60% greater than the figure which would apply to good armor (quality = 1.00).

When rounds do defeat armor despite less penetration than the resistance and the penetration probability is very low, chances are good the round will have little remaining energy when it passes through the armor, and the shell structure may be sufficiently damaged to prevent the HE burster from going off.

At Kursk, one of several 76.2mm hits on the side of a Ferdinand made it into the vehicle but did little damage.

[ March 19, 2004, 04:38 PM: Message edited by: rexford ]

Link to comment
Share on other sites


How does BFC's penetration/lethality model square with British Western Desert experience which found

that if a German AT shell penetrated halfway into the fighting compartment (not a clean penetration according to several criteria previously discussed in related threads) and detonated, it would basically destroy the tank beyond economical repair

and put the crew out of business by killing or wounding most of the men? I don't recall the reference right now, but it is locatable by searching appropriate threads under my member number.


John Kettler

Link to comment
Share on other sites

If 50% get through and 50% dont, the 50% that get through would have a minimal velocity (I would think). A direct strike by a 12 pound metal object on a person would not need much velocity though. The spall particles may still have sufficient velocity even if the main penetrator doesn't. Basically the kinetic energy could be transferred to the armor.

Its a good point about base HE making any penetration a bad thing. In the confined space of a AFV, any detonation would be hazardous to both the vehicle and the crews will to stay inside. The HE may actually re-accelerate the penetrator also. The HE blast would act like an igniter to any gunpowder from ruptured ammo or to fuel spray from broken fuel lines or fuel tanks.

I have read quite a few accounts of German APHE rounds getting into Shermans and not detonating inside. They may have had a failure or the HE detonated outside the armor itself.

[ March 19, 2004, 07:44 PM: Message edited by: Mr. Tittles ]

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Unfortunately, your content contains terms that we do not allow. Please edit your content to remove the highlighted words below.
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...