Shatter Gap, WW2 Armor Ballistics and Gunnery. I am not sure this makes sense.

[FinStabilized]

So first things first, I know the above book title had an influence on combat mission, but this post has nothing to do with combat mission and should not be viewed as suggesting anything wrong with the game. That is why I have posted in here in general discussion. From what I have observed, this effect is not modeled in combat mission (at least not as suggested in the book) which I think is a good thing.

This also should not be construed as lambasting WW2 Armor Ballistics and Gunnery, which I consider to be one of the best books on its subject matter.

 

Now to the point. I am not convinced that the description of "shatter gap" as explained on pages 29-33 of the aforementioned book makes any sense at all. As I interpret it, the book seems to be suggesting that all non-German ammo (and specifically 76mm M62) would have a tendency to fail when the penetration data exceeds a certain ratio above the plate resistance, resulting in unexpected failures. For example, at a range where a shell has 120mm 50% penetration, the round fails against 100mm of armor. The implication being that it fails more often than it should according to the 50% test criteria.

This would seem to be outright impossible, because the ammunition was empirically tested to 50% criteria. Meaning that definition the ammo was penetrating the armor of said thickness at said consistency. If the penetration chart says the round will penetrate 50% of the time 120mm of armor, than its not going to fail more often than that vs 100mm of armor. The explanation given is that some rounds may have had softer noses and the increased nose forces from shoving the armor out of the way would have resulted in shatter. However the issue is that these problems would have been worse against the thicker armor we know the round was tested to defeat. Its also hard to understand how the "laboratory" tests of the guns would have gotten their figures if the gun was found to fail consistently agaisnt a thinner plate at the same range. How would anyone have found the gun to penetrate 120mm at 100m if they ran into a apparent wall at 100mm?

Then there is the evidence that is listed, none of which appears to show anything other than what we would expect given the the penetration data. The evidence given are some Navy Ballistic tests of the 76mm gun, anecdotal evidence from combat reports, and in the field testing agaisnt captured tanks. The 76mm gun test shows some rounds failing above the expected 50% success velocity, and is taken as evidence of the shatter gap phenomenon. Except that is exactly what you would expect, since testing a 50% limit velocity requires penetrations/failures above and below that velocity. So this seems completely normal. Also the defeat velocities lists are only barely above the predicted 50% limit velocity. The same thing is true of all the field tests. These involve a very limited number of rounds fired and there are also ambiguities (like the impact against rounded armor like the Panther Mantlet) which means they dont show us anything to suggest the ammo is performing abnormally.

The anecdotal evidence I dismiss entirely because there are too many unknowns for it to be useful, especially with phenomenon suggested to occur over a very specific set of circumstances.

 

In any case, I consider the book in general to be of very high quality so I am interested in what thoughts others may have on this.

 

 

[Redwolf]

Hmmm, I need to dig out my copy.

From what I remember it made sense to me what he said, but the details are fuzzy.