47 Degree Glacis Sherman, 75mm HE Issues

[rexford]

The Shermans with the 47 degree glacis had some real weak frontal areas, like 89mm mantlet and 2" cast nose armor at 56 degrees that lost 15% of its resistance when it was hit by 75mm rounds. But the interesting thing is that the glacis provided more resistance than the Tiger E driver plate, and about the same as the Tiger nose.

2.5" rolled armor at 47 degrees resists 75mm APCBC hits like 116mm at vertical, as opposed to the Tiger driver plate 102mm at 10 degrees for 105mm. 10% more resistance on 47 degree Sherman glacis, about same as 102mm at 25 degrees slope. Pretty good, and no flaws in most 47 degree glacis tanks.

Too bad all the frontal hits don't land on the 47 degree glacis armor.

56 degree glacis Shermans with flaws might present about 95mm at vertical to 75mm hits. Big difference.

PzKpfw IVH tankers noted that their 75L48 gun couldn't penetrate 47 degree glacis at 1000m.

Further research on HE effectiveness adds to previous finding that US 75mm HE put out sa larger number of effective fragments than 76mm and 90mm HE at all meaningful ranges, and 94% of 105mm HE figure at 20' from blast.

75mm had very high percentage of total weight as HE filler and probably had thin walls, so more high velocity fragments, though they were small and lost velocity fast as suggested by data. So 75mm HE is close to 105mm at 20' in terms of effective fragments but only has half as many as 105mm at 200': data suggests that 105mm puts out larger pieces that lose velocity slower

Ricochet fire with 75mm HE has a 0.05 second delay between hitting ground and exploding, so US Army firing manual says round has to land within 20 to 25 yards in front of target to be effective with ricochet fire.

As discussed in previous threads, low velocity guns appear to be more accurate than higher velocity in terms of placing HE on or near a ground point, since flatter trajectory will have greater scatter in horizontal direction due to vertical dispersion.

So, not only does 75mm have more HE punch than 76mm and 90mm, but low velocity 75mm HE appears to better at ricochet fire due to less horizontal scatter.

The accuracy issue discussed above continues to support the need for two separate accuracies for HE fire, one based on ground target aim and another based on the ability to hit vertical targets. Low velocity better at hitting specific ground points, high velocity better at placing rounds throught bunker openings and hitting things like walls, buildings and vehicles.

German 75mm HE from PzKpfw IVH weighs 12% less than US 75mm HE shell, and has slightly heavier HE filler. US 75mm uses TNT according to British data on John Salt site, while German 75mm HE uses 60/40 Amadol (what is this stuff?). Is Amadol equivalent to US 75mm HE filler in terms of effectiveness?

Some British HE uses 60/40 Amadol, again from John Salt site.

Panther 75mm HE has less amadol than 75L48 HE, which is consistent with higher velocity HE having less filler and possibly thicker walls.

The data on German HE comes from Mark Diehl article in AFV-G2, American fragment info from TM9-1907. Conclusions are mine.

Would appreciate reader input on Amadol vs US HE filler, and anything else that comes to mind after reading through the above conclusions. I'am flexible and open to rational and factual input.

[John Kettler]

Rexford,

The weapon vs armor insights you keep coming up with never cease to amaze me. For once, though, I'm in a position to answer one of your questions.

First, I think you're looking for Amatol (not amadol), a name I've tentatively traced to a huge ammo production and filling plant built on a crash basis together with the town of that name in New Jersey during World War I.

Second, Amatol was developed as a TNT stretcher. It's therefore no surprise to me to see the Germans trying to make the most of their explosive resources by using it. Basically, its a blend of ammonium nitrate (AN) and TNT, with the ratios varying a bit from country to country. I believe the link will provide all the pertinent particulars including the all important detonation velocity. The information in aggregate should allow you to run the numbers you need in order to make proper comparisons.

Hope this helps. Thanks for your many labors!

Sincerely,

John Kettler

Amatol link

http://library.atlantic.edu/amatol/Amatol%20the%20explosive.html

[jasoncawley@ameritech.net]

On the explosives, the other fellow's link gives figures for detonation velocity of the 80/20 mixture. I ran across another figure of 3500 m/sec for 60/40 mixture, which seems to me consistent with his figure. That gives 71% or 1/(2)^.5 the detonation velocity to 80/20 vs. straight TNT, and ~50% of that ^2 to the 60/40 mixture. That is (all numbers approximate) - detonation velocity ~7000 m/sec for TNT, ~5000 m/sec for 80/20 amatol, ~3500 m/sec for 60/40 amatol, ~2500 m/sec for AN.

(Note that modern specialised ANs used in mining, with attention to crystal structure and what-not, can burn better than this - I am going by the other fellow's link with its 80/20 "almost twice" AN comment).

The explosive effect would be somewhere between linear in total charge weight, and linear in detonation velocity, I would expect. So, around 85% effectiveness for the same weight would make sense for 80/20 amatol, while around 70% effectiveness for the same weight would make sense with 60/40 amatol.

Obviously this is rough, but it will not be far off. Going by blast velocity alone would make the mixtures too poor, while going by weight alone would make them too strong. The above figures are the geometric mean of the two. Whatever error that estimate might involve is likely to be smaller than the error for either "endpoint" (by weight alone, by velocity alone), so the probably error range on the estimate, might be 5-10% (absolute figure - i.e. 80-90 for the 80/20 mix, 60-80 for the 60/40 mix).

The moral is still that the filler difference is not a minor matter. It is a large scale adjustment, comparable to the range of filler weights.

As for the weight of HE filler in the German HE shells for 75mm, I continue to have my doubts about the rounds used. You and others have in the past cited some shells with up to 860g filler, and I believe such 75mm HE rounds were made. But other types have 454g filler for straight HE, while HEAT have 500-650g in various ammo types.

The question of which rounds were most common remains, to me, very much an open one, and I am extremely skeptical of procedures that amount to taking the maximum HE load for any German 75mm shell that a gun could fire, and assuming that all HE shells fired by that gun were of that type. I call this "averaging up", and I think it leads to consistent overrating of actual performances available in the field.

Unless I see shell production numbers that suggest the 454g HE was a temporary stop-gap item and tons and tons of the 860g HE were made, I will continue to regard the former, or an average of the two, as a more realistic measure of the HE effectiveness of German 75mm.

Incidentally, on the comparison of U.S. 75mm HE with 105mm, I do not find the "fragments at 20 feet" measure a meaningful one. That is well inside the CZ for both shells on every estimate I have seen. The 200 foot figure is more meaningful, although at that distance the effectiveness of even the 105mm is likely to be low. But at 15, 20, 25 yards, I would expect a noticable edge for the 105mm.

Basically, the 75mm is not comparable in effect a 105mm round, and the comparison of what happens at ranges so close that either is effective, doesn't manage to say otherwise. I don't know that this is any disagreement; I simply offer my sense of the data you and others have given.

[rexford]

Thanks for responses.

The close similarity of 75 and 105 seemed interesting. Probability of landing a round within 20' of someone is small.

Next question: anyone have data on fuze delay times for HE other than Sherman 75mm. If faster HE rounds had shorter fuze delays on ricochet fire this would affect calculations.

Good point about using max HE filler weights, Russian ammo also presents a host of different weights and it is difficult to figure out which one is most common. Will have to ask fellow who published those figures about which was most common.

Once again, thanks so much for the responses. We're putting finishing touches on our armor booklet and all help is appreciated.