76mm HE INFERIORITY

[Guest Andrew Hedges]

This is very interesting. It is certainly well-known that tankers (at least pre 6/44) generally preferred the Sherman with the 75mm gun because of what they felt was its much more effecive HE round. Unfortunately, anecdotal evidence like this is never really quantifiable, and may have been made in a context that has since been lost (such as the German tankers in Italy in Panzertruppen who said that they would prefer to be equipped with Shermans).

It's too bad the tanker didn't say something like: we prefer the 75mm HE shell to the 76mm shell because we find it 30% more effective, especially against soldiers in woods. We estimate that it is 150% more effective than an M1919 MMG at 250m.

On a more serious note, this does seem to be pretty important information. I have a couple of thoughts.

Assuming that the 75mm sheman HE underperforms the historical 75mm HE:

1. The most significant piece of data that Rexford posted was, IMO, the data showing the chance of hitting a 6 sq. ft. target at various ranges. It's easy to extrapolate from this to what happens on the battlefield, and it would be consistent with descriptions of the 75 as the better anti-infantry shell. If the shell drops infantry 20' beyond where the 76 drops them, it's obviously better.

2. Fragments aren't the whole story, but in the anti-infantry role, they are most of the story. I would note that the 105 is about 25% (if my math is right) more effective than the 75 at 35', and that's not too shabby. To the extent that blast (and not fragmentation) matters (such as for blasting down buildings or for shells landing very close to heavily entrenched infantry), the 105 would probably be much more effective due to its higher HE charge.

3. Muzzle velocity: it would be interesting to know how much of this can be explained by muzzle velocity.

4. Field tests: Rexford, do you know how these field tests were conducted, or what the target(s) were? If the targets were ground targets, a lot of the 75 vs. 75 discrepency could, maybe, be explained by the fact that the 75mm shell buried itself 1' in the ground before exploding, while the 76mm shell buried itself 4' in the ground. This would make sense, although it might be too simplistic. It might also require different rules for shooting HE at people not on the ground. Although maybe those are already there.

5. On a completely unscientific and biased note, it would be nice if this evidence suggested that the decision not to switch to the Sherm 76 before Normandy was more rational than it seems.

[109 Gustav]

Excellent points, Andrew.

<BLOCKQUOTE>quote:</font><HR>Originally posted by Andrew Hedges:

4. Field tests: Rexford, do you know how these field tests were conducted, or what the target(s) were? If the targets were ground targets, a lot of the 75 vs. 75 discrepency could, maybe, be explained by the fact that the 75mm shell buried itself 1' in the ground before exploding, while the 76mm shell buried itself 4' in the ground. This would make sense, although it might be too simplistic. It might also require different rules for shooting HE at people not on the ground. Although maybe those are already there.

<HR></BLOCKQUOTE>

If so, than wouldn't the 76mm shell be more effective thant the 75mm when shooting at infantry in stone or brick buildings? I'm guessing that it would cause a lot more fragments and stuff, because the shell would dig deeper into the concrete before exploding.

I know that if you want to take out a building, you use high explosives, but if you want to move a lot of soft dirt, you use low explosives, which I guess explode more slowly. If anyone wants, I can try to find the reference to this.

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[This message has been edited by 109 Gustav (edited 01-07-2001).]

[Vanir]

Anti-spam bump.

[rexford]

HE tests from tank guns would probably strike at a small angle from ground level, like a few mils (thousands of a degree), and probably wouldn't bury themselves in the ground.

If a Sherman is 100m from infantry cowering in the brush and fires HE at them, the angle from gun to ground impact is maybe 1° above horizon. Burying seems a remote possibility.

HE effectiveness, after considering all thoughts in the spread, should be a function of target status.

1. Need to shoot HE through a bunker opening, hit a stone wall or knock infantry off a StuG III, got to have velocity and a flatter trajectory so U.S. 76 HE gets more FP than 75mm HE

2. Going after infantry in the open or in vegetation (including trees), 75 gets the call

3. Need to blow something up with blast, collapse a sandbag MG nest or intimidate with alot of noise so people keep their heads down, bring on the 105 and forget about the 75-vs-76 controversy

As an aside, Australian infantry in Nord Afrika found an innovative way to reduce sandbag MG emplacements when artillery could not be there. They used anti-tank rifles to knock over the bags, one by one.

Did not look at relative armor penetration between 75 and 76 HE, will do today after work.

[rexford]

While 76mm HE would have a bit more total weight shrapnel than 75mm HE (thicker walls and bigger round), it is the number of pieces and their velocity that does damage, not the total weight.

If one round has 15 lbs of shrapnel but 3 pieces due to a little explosion, and a 7 lb round puts out 500 pieces with effective velocity (sufficient velo to penetrate clothing and get through skin), which is more effective at 2' range?

Having twice the weight of shrapnel but only two pieces means the chance of hitting someone standing right next to the blast is less than 50%!

The bigger the explosion the more little pieces and the higher the velocity of the pieces, and the higher the probability of hitting someone and doing something.

Fragments and velocity is the key factor, pounds of shrapnel is almost a non-issue if the velocity and number isn't there.

We believe that the U.S. HE data is based on tank gun shots at the ground at some range that isn't listed on our pages. The blast area heavily sways to one side, suggesting it is a gun shot.

[rexford]

The total weight of shrapnel is a non-factor, the payoff is in pieces and their velocity. Here is an extreme case that illustrates the point.

A 15# HE shell with small HE detonates on the ground and breaks into two low velocity pieces. There is less than a 50% chance that folks at 5' will be hit, and even then the fragments may not be able to pierce coats and skin (low speed).

Compare to a 5# HE shell that puts out 300 high speed pieces that have enough speed to pierce infantry clothing and skin.

15# of shrapnel has no meaning if it is too slow, and does not cover sufficient area, to yield a high injury probability.

Higher TNT in 75mm means alot of high velocity small pieces, small TNT in 76mm means fewer and larger pieces that often lack the speed to do anything worthwhile.