88L71 vs. SHERMAN JUMBO FRONT

[Aacooper]

While the theoretical lather is rich, creamy and excellent for shaving, let's take a look at one (great sample size for proving points!) real-world example. This is from "The Lorraine Campaign", p.363.

On November 12th, CCA of the 6th Armored Division was exploiting a crossing of Rotte Creek as best it could in the mud when...

"At Herny, ...the column encountered a battery of 88mm anti-tank guns, heavily supported by German infantry... Finally one of the 69th's headquarters tanks, a new and heavily armored model [footnotes state it was a M4A3E2], made a frontal assault on the German guns, taking seven direct hits without pausing, and enabled the medium tanks and tank destroyers to flank the position and destroy the battery."

Now, the range of the encounter isn't specified, but Herny is in front of a higher ground. The map in the book doesn't show a hill in the area, so the higher ground might be a plateau. The Lorraine terrain in the area is fairly wooded, though a photo of nearby Han-sur-Nied shows open fields. I think it is unlikely that the range of the encounter is more than 1600m, because without commanding heights in the area, Herny is probably in defilade from higher ground to the east.

Another possibility is that the German guns were smaller than 88mm.

But that's one example of a Jumbo's survivability in action.

[Guest machineman]

Saw this in the Panther Fibel on the Desert Fox's site, an illustration of penetration at different slopes.

[This message has been edited by machineman (edited 01-06-2001).]

[Spook]

<BLOCKQUOTE>quote:</font><HR>Originally posted by rexford:

TOBRUK had a hit resolution table where 30% or more of the 88mm Flak hits on the Stuart side armor would fail to damage the tank, due to angle and other considerations. U.S. penetration data clearly shows that 70° and 75° slope armor can be penetrated, and naval test data shows the same result for up to 85°.

(snip)

Angle alone will not cause a high percentage of ricochets, if it did we would see alot of 15mm at 80° glacis plates.<HR></BLOCKQUOTE>

Yeah, I remember a contributor's article in the Avalon Hill "General" (in the 1980's) that pointed out how the "Tobruk" game allowed a very high proportion of 88mm hits on a Stuart to "richochet." In fact, that article suggested that 2/3 (!!) of 88mm hits were richocheting off of Stuarts in that game.

Certainly, angle alone isn't the singular factor to shot richochet. But it isn't a linear factor either, by trigonometric considerations. Or to describe by example, a plate's 10-degree rotation, from 25 degrees off of vertical to 35 degrees, will not have the same richochet impact as a 10-degree rotation from 70 degrees to 80.

The reason we don't see see glacis plates of 80 degrees (from the vertical) and 15mm is that it require a LARGE vehicle to extend out such a glacis without a sudden angle-down due to size, length, weight considerations. Not very economical.

This is straying possibly into apples-and-oranges, but one could look at the modern US M1 tank series by example. Its glacis section is very shallow (or rather, approaching 90 degrees off of the vertical), but connects to a full-hull plate that is nearly vertical. I don't know offhand what the glacis armor of the M1 (or M1A1) is compared to the front hull plate, but I doubt it to be equivalent.

That's a limited example that can be spun off into distracting (and erroneous) conclusions. But in balance, rexford, I do concur that "other factors" have to be considered too (like the quality of the shell & armor metal) beyond just armor angle, and CM already does this to some extent (like armor quality). And I further concur that extended ranges can make the measurement of "penetration factors" more difficult.

[Jarmo]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Aacooper:

[bAnother possibility is that the German guns were smaller than 88mm.<HR></BLOCKQUOTE>

Or that the 88's were not L71. There are different models.

The one on the Tiger I doesn't have anything to say to Jumbo.

[Aacooper]

Did the Germans have an anti-tank 88 that wasn't an L71? CM doesn't, but I certainly no expert on the small details of German arms.

The book is clear that Jumbo turned back anti-tank gun fire, not tanks.

[Gremlin]

Tiger Ausf. E had the KwK 36 L/56. By the nomenclature, I assume that's a 56 caliber (length) 88. I think all the other AFV and AT gun 88's were 71 calibers long.

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

I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones.

--Einstein

[Jarmo]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Aacooper:

Did the Germans have an anti-tank 88 that wasn't an L71? CM doesn't, but I certainly no expert on the small details of German arms.<HR></BLOCKQUOTE>

At least there's the 88 Flak. I doubt the allies would spot

the difference. It was often pressed into AT role, for it did

such a good job at it.

[Gremlin]

I just read further that the KwK 88 was essentially the 88mm Flak 36 modified for a tank mounting.

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

I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones.

--Einstein

[rexford]

Oops! Meant to say in last message that few or none of Panther hits on 20mm at 70° glacis at 0m to 2000m will fail to penetrate.

[rexford]

Machineman's post shows that when round hits armor with fair slope it penetrates downward.

Americans were so afraid of Tigers that they often identified PzKpfw IV's as Tigers. 88mm Flak was an anti-tank gun to a Sherman tanker. Unless someone went up to enemy position and made positive ID it was often impossible to verify battle accounts.

What makes 4 hits in 4 shots by M18 at 2000 yards a lucky string is that 95.5% of shots would be within 4' vertically of aim point, so hitting StuG on one shot entails some luck at 2000 yards.

M18 commander called for lead based on 2 second flight time, it actually was 2.8 seconds to target. Still made four straight hits.

[rexford]

Rounds basically ricochet because penetration isn't sufficient to accomplish plate defeat. If penetration is sufficient, rounds almost always go thru unless one of the factors that don't show up on the firing range raises its' head.

[Spook]

<BLOCKQUOTE>quote:</font><HR>Originally posted by rexford:

Rounds basically ricochet because penetration isn't sufficient to accomplish plate defeat. If penetration is sufficient, rounds almost always go thru unless one of the factors that don't show up on the firing range raises its' head.<HR></BLOCKQUOTE>

I could well be misinterpreting that statement, rexford, but machineman's posted graphic seems to counter this to some degree. I checked the graphic by saving it into a Canvas file, opening, and checking the relative "armor" thickness and plate angles.

The plate shown at bottom is basically equal to the top plate due to the "sloping" effect (and recognizing in both cases that shell trajectory is virtually horizontal). But the angle off from the vertical is about 50 degrees.

[LynnL53]

I saw an earlier post with something from the desert fox site -- were would I find that site -- it looked interesting thanks

[rexford]

The hit at about 45° penetrates the plate and heads downward after defeating the armor.

The hit at a greater angle from vertical (the lower picture) faces too much effective armor resistance and drives into the plate and is pushed upward, plate wins and projectile loses. The defeat angle looks lile about 55° or 60° from vertical.

Whether or not a ricochet results depends on effective resistance of armor compared to penetration of projectile.

Hits at an angle win by pushing a plug out of the armor, the round follows the plug.

[Guest machineman]

Angle (from the horizontal, I believe) is given at the beginning of each 'film strip'. Lynn, the address of the site is:

http://www.geocities.com/Area51/Capsule/2930/

[Spook]

I re-checked, rexford, and actual angle from vertical for the lowest plate is 60 degrees. (I mixed up tangent with sine, doh!) I could see the numbers, machineman, but for the last plate, the number was hard to read. To your comment below on that last plate, rexford:

The hit at a greater angle from vertical (the lower picture) faces too much effective armor resistance and drives into the plate and is pushed upward, plate wins and projectile loses.

From my measurement (zoomed in), the relative thickness on the horizontal plane is the same as for the vertical plate.

Thereby, the shot richocheted.

Perhaps we're getting into parsing of terms on "ricochet." In a pure ricochet, the projectile would bounce off into another direction without a loss of kinetic energy and with no deformation to either the projectile or static plate. That isn't the case here, of course.

It's a basic concept in engineering dynamics, rexford. The increase of angle from the vertical causes a reduction of the "normal force" (perpindicular) that the plate must exert ot resist the projectile. And again, this magnitude of reduction isn't linear with angular change.

Of course, the plate can be so thin so as to be unable to apply the needed resistance force against a given projectile, regardless of angular setting. But that's not what the graphic is showing. It's showing "equal thickness" relative to projectile trjectory.

[This message has been edited by Spook (edited 01-06-2001).]

[rexford]

If plate thicknesses are equal, plate at 60°from vertical resists hits better than 45°, and that explains why one case penetrates and the other bounces after digging in for awhile.

Armor resistance determines if hit goes through or flies off.

[Spook]

That's just it. The true plate thickness (measuring perpindicular to the plate plane) doesn't APPEAR the same for the vertical plate shown on top and the plate shown on the bottom, angled off from the vertical.

What I measured from the graphic is that if you measure a horizontal line segment across from one plate surface to the other, the segment will have about the same length for either plate. Thereby, the thinner plate at the bottom of the picture has been rotated in such a way that its "effective thickness," relative to the horizontal, is about the same for the vertical plate.

However, my measurements are making one possibly erroneous assumption: that each photographed plate is truly scaled to the others. And regrettably, I can't translate the German language in the picture. Does anyone who can read German know if the picture says that each plate in the picture has the same TRUE thickness?