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sandbagged shermans?


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I see that the 76mm M4A3E2 Jumbo has been added to the US vehicle list. That is great.

I was wondering if there was any thought as to having the common sandbagged armor on the shermans. Alot of the shermans after Oct-Nov 1944 were field modified to carry the sandbagged armor. This is especially true of the attatched armor battalions who faced german infantry more.

There are critics of the sandbag armor that say that it was totally ineffective. But there are books from the vets experiences that claim that many of the panzerfausts would bounce off of this armor and also absorb the blast. The sandbags that were the most effective were ones that were mixed with cement and water to make the sand hard and concrete like. This was very common and I feel it was fairly effective in standoff protection against HEAT weapons depending on the depth of the sandbags. The only problem was that each hit would remove some of the sandbags.

The argument against the sandbags is that there ar many pictures of knocked out shermans with sandbag protection, even ones knocked out by panzerfausts. This being the case, out of all of the pictures of the knocked out shermans I have never seen one that was actually hit in the sandbags. Most pictures look like top hits from windows and buildings. Wondering if this could be added to the game?

Also the field armored M4A1 76(W), don't know if the earlier post was seen, but it was quite common towards the end of the war. I would e-mail you pictures of the mod. but I don't have a scanner. Very good video of these in the Chronos Video from Remagen to the Elbe. Also talked about in "Death Traps" with picture in "Sherman in Action" from Squadron.

Anyways keep up the awesome work!!!

dano6

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<BLOCKQUOTE>quote:</font><HR>This was very common and I feel it was fairly effective in standoff protection against HEAT weapons depending on the depth of the sandbags.<HR></BLOCKQUOTE>

As for the commonality of this ad hoc armor modification, I have seen original war footage of Shermans with sandbags on them and they are usually rolling along in column with other Shermans that do not have sandbags on them. I have also looked in the books and found in most pictures of Shermans after 10/44 they do not have the sand bags on them. This may be because the war photographers did not want to take pictures of the less graceful looking sandbagged tanks though, I do not know. It seems to me that if this "upgrade" was as effective as you say the Army would have issued general orders for the rest of their tanks to be so modified. This is not to mention the word of mouth endorsement "hey Bob, Joe's tank got hit yesterday by a Panzerfaust, right in the old sandbags, and he survived!" "Really? that's great, I'm going to tell the whole platoon to start stacking sandbags right now!". I would bet that this was looked upon more like "what ever brings you luck". I would guess that it was marginally effective at best and that is why it was applied to the tanks in a rather haphazard manner.

It is just a guess here but I would tend to think that the non-cemented sand bags would be more effective in that they would distribute the energy of the explosion to more individual pieces rather than the cemented bags which would tend to shatter into a relitivly few pieces. In Vietnam they used sandbags (non-cemented) in and on the APC's and the Tanks. These were applied not as extra armor against RPG's but as mine protection for the crew and the soldiers that ride on top of them.

<BLOCKQUOTE>quote:</font><HR>Most pictures look like top hits from windows and buildings.<HR></BLOCKQUOTE>

Boy this would be a brave PF operator! If the infantry supporting the tanks had swept the tanks avenue of approach properly, stuff like this would not happen. German standard practice for using the PF would be to try to get a side shot before firing. The PF could take out a Sherman from the front but who is going to wait there while a Sherman advances with it's guns (MGs included) pointing at you. smile.gif

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Rhet

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I see no reason why sandbag armor wouldn't be effective as a sort of reactive armor, assuming the space was large enough. I can't imagine they'd offer anything signifigant against AP though. Where exactly did they put the sandbags? It seems like it would be difficult to get good coverage (percent wise) and good standoff over a signifigant portion of the tank.

My guess is that placing sandbags on the tank was one of those "try anything, it might help" ideas.. sort of like mounting tracks links on the front armor.

Chris

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Guest Scott Clinton

Sand-bagged armor was very common.

In Hunnicutt's Sherman book (the undisputed source on Sherman's--only $70 now at Amazon btw) there are prob. over 100 photos of Shermans with sandbags and REAL concrete POURED onto the hull.

In one phote in particular is shows and ENTIRE Canadian Battalion lined up with each and every single one having extra tracks welded onto the hull and turret for added protection. IMHO even a humble track welded on to the turret would add at least another 1/2" of armor...nothing to sneeze at when you only had 2" to start with!

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The Grumbling Grognard

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Rhet,

As to the commonality of the sandbag armor, you are completely wrong to say that it was not common. Each armored division and attatched tank battalion had its own view on up-armoring the sherman. The 14th armored division used the sandbags on every single sherman in its division including its own 105 shermans.The sandbags were applied by the tank maintenance battalion and engineers attached to the division or battalion.

Lets see who else used the sandbags:

781st tank battlaion attatched to the 100th inf. division

747th tank battalion(don't know attatchment) also used welded tracks underneath the sandbags.

37th tank battalion, 4th armored division

750th tank battalion, 75th infantry used concrete armor on the fronts of tanks as well as sandbags.

I also don't know the numbers of all of the tank divisions that used this but I'm sure there are more.

Oh and again the entire 14th armored division.

That makes for quite a bit of shermans covered in sandbags. Also in Patton's 4th armored many tanks went to the sandbag armor and were reprimanded by Patton because he felt the added protection was not worth the weight on the chassis.

As for the effectiveness of the sandbags, it was primarily against HEAT weapons. This was due to the standoff capability of the hard sandbags. There is no absorbtion of kinetic energy on a HEAT round therefore the loose sand would have little effect because the loose sand would be blown out by the initial explosion of the HEAT round. The cemented together and hard sandbags that were used more often would resist the initial explosion easier and would then give a resistance to the HEAT stream from the panzerfaust. I will search for the quotes from tankers that actually back this up in the many books that I have read written by US tankers themselves.

As for the other armored divisions many welded extra plate armor over the front glacias plates. By March 1945 I would say there were more field modified(up-armored) shermans than there were unmodified shermans. And by the end of the war, almost every sherman was field modified(up armored) in some way.

dano6

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<BLOCKQUOTE>quote:</font><HR>As to the commonality of the sandbag armor, you are completely wrong to say that it was not common.<HR></BLOCKQUOTE>

Dano6, it appears so. wink.gif In my defence though, I went back and looked at the footage (only footage I have that is definatly after 10/44)and it could be clearly seen that the sandbags were not applied to all of the tanks in the column. The footage is from the Ardennes so it could be Pattons tanks, and as you said not applied to all his tanks.

<BLOCKQUOTE>quote:</font><HR>As for the effectiveness of the sandbags, it was primarily against HEAT weapons. This was due to the standoff capability of the hard sandbags.<HR></BLOCKQUOTE>

The best way to defeat HEAT weapons is to disrupt or dissipate the flame jet that is created by the shaped charge. This is the principle that spaced armor (meaning armor plate mounted in a standoff fashion) was developed by. The flame jet upon burning through the outer plate dissipates in the "free atmosphere" that is between the outer plate and the armor of the tanks hull or turret. Even this method, which I believe was the most effective method of the war, was not 100% successful. Modern reactive armor uses a counter explosion to disrupt the flame jet and is the most effective defence from HEAT weapons to date. Since I do not have empiricle data or a computer model for the following I would like to stress thatwhat follows is based on imagineering only! smile.gif The "cemented bags" are not filled with high strength reinforced concrete they are for a lack of a better term filled with poor quality brick mortar. They would indeed withstand the initial impact and explosive blast of the HEAT round better than the non-cemented sandbags. But, I believe that the cemented bags would confine the flame jet (instead of allowing it to disperse) and thus allow the heat energy of the jet to be maintained and thus delivered more directly to the tanks armor. In my earlier post I was talking about the explosive energy released by the HEAT round not the flame jet.

More "standoff" can indeed be provided by laying more layers of either type of bag but this will reduce the tanks reliability and cross country performance which I believe was one of the real assets of the Shermans.

Note: one layer of "dry" sandbags/concrete sandbags (est. 4" thick) on the front and top of the hull only would add approximatley 2.75/3.5 tons to the weight of the tank respectivley.

<BLOCKQUOTE>quote:</font><HR>There are critics of the sandbag armor that say that it was totally ineffective.<HR></BLOCKQUOTE>

I am not one of these guys! I am just saying that the benefits would appear to be marginal with this method.

<BLOCKQUOTE>quote:</font><HR>Wondering if this could be added to the game?<HR></BLOCKQUOTE>

The guys at BTS are very much into modeling the real aspects of the vehicles of the war. You have provided proof that enough tanks were up armored in this fashion that they should take this into account. I have seen many types of application of the bags. It ranged from what appeared to be one layer of bags on the front slope and top of the hull to welded racks on the front and sides that looked like they held two bags deep (the latter shown in World War Two tanks, George Forty, p148). The variation of these applications, I believe, will make the modeling of this "uparmoring" more of a composite thing though. I don't think they will develope a new vehicle "sandbaged Sherman" for the vehicle list though. wink.gif

Respectfully,

Rhet

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Guest Big Time Software

Charles will have to weigh in on the sandbag issue, but I personally don't think the sandbags would do much good. Not only do Rhet's thoughts seem correct to me, I am pretty sure I read that the sandbagging did nothing but boost (falsely) the morale of the crew. Remember, sometimes totally ineffective things are done on a small or large scale simply because someone THINKS that it is worth the effort.

The problem with simulating crew up-armored vehicles is that there were SO MANY different methods, in different places on the same vehicle types. Some put roadwheels, others tracks, wood, sandbags, sheet metal, whatever... Generally I have read that these things were of marginal, if any, value. The famous shot of two smoking Shermans with sandbags (you all know the one I am talking about smile.gif) from 14th Armored in 1945 might prove this as they were most likely knocked out by Panzerfausts. I also doubt the shots were taken from above street level either. This was near suicide as routes of escape would be easily cut off.

Steve

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Guest Big Time Software

In addition to what Steve said, there's a very good reason why we're not specially simulating sandbags: They didn't work.

I think we're all in agreement that the sandbags were little, if any, use against AP rounds.

Some folks believe that the sandbags would have been more effective against HEAT rounds, however, because they would provide extra standoff range. While the standoff range would indeed be increased, it's highly unlikely that it would be increased to the degree required to stop a round from otherwise penetrating.

The reason is simple: according to the HEAT standoff-vs-penetration curves I've seen, you'd have to add TWO FEET of standoff simply to reduce a panzerfaust penetration by 50%. Not only is two full feet of sandbag thickness rather difficult to imagine (I've never seen them loaded up THAT thickly) but even a PF at only 50% effectiveness is still easily powerful enough to burn through a Sherman's armor at virtually all angles. Eight or twelve inches of sandbags might reduce the PF by about 20-25%, which is nowhere near enough to save the tank. PFs just have too much excess penetrative power.

In all my research I have yet to come across a single example of a vehicle surviving a PF hit due to sandbags. The benefit was psychological, not actual.

Charles

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Although it is convenient to think that HEAT rounds burn through the targets armor like a super hot cutting torch, this is not the case. HEAT rounds use the energy of a focused explosion to punch a hole through the armor of the target. Spaced armor works by moving the point of focus farther from the main armor of the target. However, there is a danger that using sandbags or other field expedients to provide extra armor could actually improve the penetration of the warhead. This is because there is an optimum standoff range for any HEAT round and it is not always practical to provide that amount of standoff in round that must be carried by infantry or manuevered within the confines of a turret. So the application of things like sandbags and track sections which have little or no armor value can actually move the focus of the blast to closer to the optimum distance.

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If something cannot be fixed by hitting it or by swearing at it, it wasn't worth saving anyway.

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I know that the "hot jet of gas" analogy for a HEAT round is really correct, but why then is composite armor more effective for stopping HEAT? The only value I could see for ceramic would be that takes quite a lot of energy to melt it. Does anyone know how ceramics are used in modern armor? Alternating layers? Fibers? Honeycomb? Anyone wanna explain Chobham armor to me while your at it? I promise if you do I won't tell anyone else.

Chris

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Guest Big Time Software

Chris, I don't know much about modern composites, but the main reason they are better is that they are lighter and stronger, therefore can be made thicker and even more resistant to things like HEAT. I also recall something about the ceramic stuff absorbing more of the enegergy, which makes sense to me wink.gif

As far as how it is made... all I know is that the process means it has to be in flat slabs, hence the angular look of MBTs that have this kind of armor.

Steve

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Think about the fact that the heat shielding on the Space Shuttle is a type of ceramic material and that might help one think of the possibilities.

I think one problem with discussions on this is none of us know anything for sure since this stuff is so secretive.

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Guest Scott Clinton

Another BIG reason why composite materials are much more resistant to HEAT warheads that is completely being missed (IMHO) is that they are by definition a ‘composite’ of several materials. Thus, the HEAT ‘jet’ does not just penetrate a single piece of homogeneous plate, no it must contend with various materials with various densities, various melting points and flash points. Sort of like what a ‘faust would have to contend with as it detonated against a sandbag and then had to burrow through successive layers of compacted sand, concrete and armor plate.

Now, back to the game at hand...I don’t think it is really a top priority that ‘sandbagged armor’ be modeled. And if it were it would be damn difficult to do! You would have to have a variable on what type of added armor was on your tanks as well as to how well it actually preformed when hit! Maybe in CMs third sequel (a return to the Western Front) ;)

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The Grumbling Grognard

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<BLOCKQUOTE>quote:</font><HR>I know that the "hot jet of gas" analogy for a HEAT round is really correct, but why then is composite armor more effective for stopping HEAT? The only value I could see for ceramic would be that takes quite a lot of energy to melt it. Does anyone know how ceramics are used in modern armor? Alternating layers? Fibers? Honeycomb? <HR></BLOCKQUOTE>

For answers to these questions and more go to this address:

http://lib-www.lanl.gov/pubs/number17.htm

The report titled Armor/anti-Armor materials by design is most informative.

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If something cannot be fixed by hitting it or by swearing at it, it wasn't worth saving anyway.

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Harold, do you know of a place where this information is available in something other than PDF? The PC I use to surf the web isn't my own, it doesn't have an Adobe-type PDF reader, and I'm not supposed to download and install plug-ins willy-nilly (I love that phrase!)

Failing that, could one of you kind people out there maybe download it, convert it to a Word (or even plain text) file format, and email it to me? I'm really curious about the "how does Chobham work" thing, and would appreciate it very much. My email is listed in BTS, but for the record it's

socrates1@home.com

'Zsanks!

DjB

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This is my final post on this subject. I spent last night looking through all of my books for a quote from an US tanker describing a panzerfaust attack against the front of his sandbagged tank that did not succeed. In the quote he called the panzerfausts "footballs". To my dismay and wasted time I could not find the story. Found other interesting things though. The 743rd tank battalion believed that sandbagging of the shermans stopped many AP rounds and panzerfausts(view from the turret)from penetrating.

My own view after a little research:

Upon looking at pictures of the typical sandbagging that occured after August 1944, I took a scale to the pictures and determined the average pile of sandbags on the front of the sherman to be 1.4 ft. perpindicular to the glacias plate. The rest of the bags on the sides and turret amounted to .92 ft. Some shermans had up to 2 ft. piled on the front of the tank. But the average of 12 pictures was 1.4 ft.

If you take the effective thickness of the bags to an AP hit at say 7 above degrees above the horizintal. You get an effective thickness of 1.73 ft. of cemented sand and gravel. I believe that this would definitely have an effect on an AP round. Perhaps a 20% reduction in velocity maybe more. How many of these walls would the round go through? Some kinetic energy would have to be lost due to friction and the energy spent breaking the slurry type cement mixture. While I know this would have little effect on the super high velocity german guns such as the 75mmL70 and the 88mmL71, It would definitely have an effect on the 75mmL40, 75mmL48, 50mmL60, 88mmL56 guns the germans used. The effect would have to be there because AP round had a hard time penetrating concrete. While I know that the sandbags are not reinforced conrete, they have to provide some form of absorbtion of the kinetic energy of the round. To just ignore this is to say that an AP round would go through everything.

Forces that would be taken into effect would be the force to shear the concrete from its surrounding addhesion and also the friction as the round passes through the hole. Both of these would absorb some of the energy of the AP round. This would occur for at least 1.73 ft. and more if there was an angle in the x,y,z plane.

Now for HEAT (panzerfaust hits) earlier posts by charles state that the HEAT stream will travel 2 feet with the panzerfaust before it breaks up. From what I have read the Panzerfaust 30, 60 and 100m all had penetrations of 200mm. So if the faust hit the front glacias of the tank at 25 degrees to the horizontal the effective sandbags would be 1.5 ft. thick. I believe that this would have to impede some of the HEAT stream as the slurry would not melt as easily as steel. As for the force of the stream some of it would definitely have to be absorbed in the penetration of the concrete-slurry. And remeber once it got through the bags it would still have to penetrate 60-80mm efective steel armor. While I don't know how much would actually be absorbed by the concrete-slurry it is something to think about.

Anyways I wish I could have found that story about the sherman and the fausts(it is a really good one becuase it stuck in my mind) but I got sick of researching, too many damn years in college I guess.

I guess the sandbags are probably too difficult to model for this game, and most people here feel that they were not effective anyways. I, on the other hand, like to believe that the people who actually rode in the vehicles knew what they were talking about. Some of the tankers actually believed that the sandbags were quite effective. I can't imagine an experienced tanker spending the huge amount of time to upkeep the sandbag armor on the vehicles if it did not present some sort of protection. Also it is hard to imagine an experienced tanker willingly giving up some of his mobility for ineffective armor upgrades. As for a moral booster, I would think that the tankers would initially be thrilled with the sandbags until they saw they didn't work, at which time they wouldn't still maintain and install new sandbags. The 743rd regularily maintained and gave credit to the sandbags for saving many lives from Aug. 1944, to May 1945.(view from the turret)

Seems like too much work for the letdown if they had no effect on either the AP rounds or panzerfausts.

I know the army has plenty of moronic orders and makes people do stupid ass things. But soldiers on their own intitiative did the sandbagging.

Just thought it would be cool to see some hell-of-sandbagged shermans running around with some better protection value on them. They just look so damn cool, at least I think so.

Still can't wait for this game, keep up the great work

dano6

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Guest Big Time Software

<BLOCKQUOTE>quote:</font><HR>I know the army has plenty of moronic orders and makes people do stupid ass things. But soldiers on their own intitiative did the sandbagging.<HR></BLOCKQUOTE>

Don't be so sure soliders know what they are doing when looking at a huge sample wink.gif There are plenty of examples of soldier views that don't survive when examined. One of them was putting wood and logs on the sides of tanks. Roadwheels even wouldn't do much, if anything. Charles has also shown that extra tracks (a particular favorite of the Germans) wouldn't do anything. Then there is the zimmermit paste on the German tanks. I also remember several US vets in a row swearing that the BAR was the biggest hunk of junk the Army ever issued, yet a survey found that a majority of soldiers would take that as their first weapon.

I'm not saying that vets are wrong all the time about everything, but sometimes their view of what is "right" is not always correct. This shouldn't surprise anybody. Take any sampling of a couple thousand men and ask them the same question about some reality. I bet you get back several different and conflicting answers.

Oh, and then there is also lots of other human nature at work on the battlefield. The "well, we did it because we felt it would work, and that is the story we are sticking to" mentality. Or how about "well, it didn't work for him, but I am sure it will work for me". And the always present "it's better than nothing" view. This last one was something that Allied tankers had in droves IMHO. Their armor was so thin that they figured that anything they could do to make it thicker was better. These guys did not have backgrounds in physics an ballistics, or lots of data on German penetration values. I know about the latter because I have several handbooks the US Army gave out and they lack all of this info.

In short, I put my faith in physics, which so far as I can tell say that sandbags don't do squat wink.gif They do, however, look really cool...

Steve

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Guest Big Time Software

<BLOCKQUOTE>quote:</font><HR>Seems like too much work for the letdown if they had no effect on either the AP rounds or panzerfausts.<HR></BLOCKQUOTE>

Dano, I think you're giving too much weight to the tankers' opinions about the effectiveness of sandbags. Keep a couple of things in mind:

1. It's hard to prove a negative. Thus, in combat, if a tank got knocked out despite the presence of sandbags, a tanker might say "Well, if the incoming round had been a little more off to the side, then the sandbags would have worked." And even if he's dead wrong, it's awfully tough to prove him wrong on the spot, when you're just a 1944 tanker with no history books and no detailed analysis or performance specs of German weapons and American armor to refer to, like we have today.

2. Sherman crews were sometimes desperate to find a way to survive heavy panzer and panzerfaust threats. Many carried good luck charms into battle but Combat Mission won't model those either. smile.gif So the use of sandbags smacks more of desperation than a sound judgement of defensive capability.

3. American tank crews were given shockingly sparse training and information concerning German weapons, therefore their opinions were not necessarily informed ones. Remember we thought that the 76mm gun would take out Panthers with no problem. Antitank engineering was cutting-edge at the time and the average tanker did not understand the mathematics and principles behind the weapons and armor, especially something whiz-bang like a HEAT round. Thus, in his mind "some" protection was better than "none".

4. Apparently the sandbags didn't hurt the Sherman's mobility too terribly much. The problem was one of wear and tear, and breakdowns were more frequent and greater maintenance was required. But a breakdown is rarely life-threatening to a tanker, so he'd much rather risk that even if the protection from sandbags is unconfirmed. In his mind, at least the sandbags might work, and might save his life, so if the only price to pay is occasional breakdowns (which ends up being someone else's problem), then why not do it?

5. None of us has been able to find any evidence of sandbags protecting a Sherman from a hit that otherwise would likely have penetrated. Not a single example. If it really worked, I bet even more Shermans would have used sandbags. But they didn't.

<BLOCKQUOTE>quote:</font><HR>I took a scale to the pictures and determined the average pile of sandbags on the front of the sherman to be 1.4 ft. perpindicular to the glacias plate.<HR></BLOCKQUOTE>

You said that the average thickness of sandbags is 1.4 feet. I disagree. The ranges I see are more like 6 to 12 inches. Once in a while it might be slightly thicker, but this is usually when the sandbags have fallen out of place and are arranged sloppily, with big gaps. 1.4 feet is more like a maximum, not an average. And even 1.4 feet of sand and low-quality concrete wouldn't have much effect.

Further, this is the actual horizontal thickness of the bags, not the "thickness before considering slope", so you cannot multiply to get a "sandbag thickness basis" like you would with normal armor. So the 6-12 inches is all you get. This is virtually worthless against AP rounds. I'm not saying is has zero effect, literally, but the effect is small enough that it's not worth modeling.

And 6-12 inches of extra standoff might actually improve the penetrating power of a HEAT weapon like a panzerfaust, as Harold Jones mentioned.

Charles

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Another factor that would limit the usefulness of the sandbags in that they are still just alot of individual bags, even if you do add concrete. Its like a wall built of sturdy bricks, but without any concrete, fairly easy to knock down.. especially when your hammer is an 88. The same I think would be true of a heat round.. They don't need to "burn" through the sand first, the explosive jet just knocks them out of the way.

Mind you, if you told me I was gonna have to ride around in one of those deathtraps, I'd be piling everything I could find up for a bit more protection.

Chris

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Harold, you dog! wink.gif Thanks for your post. I am a great believer of "you learn something new every day". I had read many books that talked about the "flame jet" developed by HEAT rounds so I was suprised by your post. It prompted me to do a lot of research on HEAT weapons and armor. I even called a friend (mechanical engineer) who works for the Army in weapons R&D (Abrams Projects). I will go over a few things that were brought up during this thread in hopes to provide a little more clarity to this issue. This maybe a little long but if you bear with me there is some cool stuff he told me about.

First things first, a HEAT round... upon detonation of the round the cone shaped explosive deforms a malable metal liner. The liner which is basically turned inside out, heated and compressed forms a pressure jet which is what strikes aginst the armor. This jet is made up of solid metal (from the liner) but it behaves as a liquid due the the emense pressure of the explosive charge. The velocity of this jet in modern rounds is around 31,000 feet per second (approx. 21,000 mph!). He said that the velocities of the WWII HEAT rounds would probably be a little lower due to slower burning explosives that were employed. This fluid like metallic jet does not actually "punch" through the armor but pushes the metal out of its path. Imagine blowing real hard into a bowl of pudding. wink.gif This is why the metal around the point of penetration appears to be melted. It is infact not melted it has just deformed in a fluid like manor. I imagine it is this aspect which leads people to believe that it burns its way through the armor (myself included). redface.gif

As to the standoff distance and the focusing of the jet. Modern HEAT rounds actually have a stand off tube called a "spike" which allows the jet to stabilize (reduces tubulance within the jet stream) before it comes in contact with the target. The PIAT which was developed and fielded by the Tommies and the panzerschreck (Gerries) had such a device but it was not as effective as modern "spikes". The others such as PFs', wurfmines, AT grenades and'zookas did not use this tube system to stabilize the jet. So there is no real "focus" distance for the HEAT round just a jet improving device. Modern rounds depend on this so that they can penitrate as much armor as possible with the charge that is carried (sort of a more with less thing but I won't get into that again wink.gif ). My friend said that the earlier warheads (without spikes) would have had the geometry of the round (internal & external) optimized so that the jet would be properly formed by the time it impacts the armor face. Or optimized as far as their sliderules could take them. smile.gif To my relief, he said that the physics that I described in my earlier posts were essentially sound. If the jet is contained in a channel such as the standoff spike or the tunnel it is creating in the armor it remains powerful. If the jet is able to vent to a free environment the pressure dissipates from the jet and reduces its effectiveness.

I questioned him about the HEAT rounds -vs- Sandbags. He first chuckeled... then said that they would have only a marginal effect if not neglegable. The velocities and pressures involved are far to great for them to reduce penetration by an appreciable amount.

This is getting kind of long so if anyone wants me to go into Chobham and Reactive armor systems just let me know and I will add another post covering these.

BTW I told him "of course my Physics were correct, I got better grades in it than you did". To this he retorted, "yeah but I kicked your Ass in Dynamics and Thermodynamics" Who said engineers are not competitive. wink.gif

P.S. thanks Dano6 for bringing this topic up, it has been a great learning experience. Maybe Steve or Charles can code up a sandbagged Sherman as sort of a tribute to this thread. wink.gif It has the same protection of the non-sandbagged Sherman but costs an additional point to purchase. Call it a beauty tax. biggrin.gif

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Rhet

[This message has been edited by Rhet (edited 07-08-99).]

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Welcome back to as the turret turns... when we left off last time Joe and Tommy were in desperate trouble as Klaus's 88 was targeting their tank... wait, sorry, different thread entirely! Oh yes, modern armor types...

Chobham armor is a type of composite armor that was developed to provide a higher level of protection from HEAT weapons. The word "composite" in this case does not mean carbon fiber or any other specific engineered material that this term is commonly used for nowadays. Instead, it simply denotes that an item is made up of more than one distinct type of material. In the case of Chobham armor these materials are steel and ceramics (not the coffee cup kind of ceramic either smile.gif ). The ceramic material is sandwiched between two plates of hardened steel. Now onto how composite armor behaves when hit by a HEAT round...

The steel (being relitivly ductile) on the outside of the composite "sandwich" acts as a shock absorber for the ceramic material. It absorbes the initial impact of the round and starts to dissipate the energy of the pressure jet. This is important because the ceramic is very hard and very brittle. The pressure jet has now reached the ceramic material. Ceramics have a very chaotic molecular structure compared to the very orderly crystaline matrix structure of metals. This chaotic structure does not allow the pressure jet to push the material away in an orderly straight line fashion as it does with the steel. As a result the concentrated force of the jet is broken up and forced to take irregular pathways and/or split into numerous weaker jets. This splitting of the jet is the real key. The law of conservation of energy dictates that the energy of the original jet is equal to the combined total of the smaller jets minus the energy expended to the displace the armor. Basically this means that you now have more jets but they lack the indivdual concentrated force of the original jet (loose any one yet? wink.gif ). As a result, these weaker jets do not penitrate as far as the original jet.

Chobham armor is fitted in flat plates because the ceramic "meat" of the composite armor sandwich is fashoned in a honeycombed structure. It is my understanding that this honeycombed structure cannot be bent, if it is the cells of the honercomb loose their structural rigidity. This has a some benefits, it is lighter which allows the thickness to be increased and the honeycomb allows for the pressure jet to vent along different paths more readily. The Russians can bend their composite armor. I was told that we do not have the technology to do this but I believe that they are not using a honeycombed ceramic so they could just cast the ceramic to the correct curve. This is just my guess though.

Stay tuned for the next installment Reactive Armor. Same CM time, Same CM channel. wink.gif If anyone has questions on chobham I will try to answer them in my next post.

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Rhet

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Guest John Maragoudakis

Here's a silly question. If the front armor of a tank was sloped forward instead of backwards, wouldn't that cause some of the energy of an incoming round to lift the tank thus disipating some of it's energy?

Timewarp back to 1942, John convinces his whole battalion to try it. The turrets are taken off and turned upside down. It's gotta be better than nothing. smile.gif

But doesn't it make a little sense though?

Next I'm working on the rotating armor plate on the turret concept. When the round hits the plate, the plate spins around, absorbing some energy and redirecting the round. Mad scientist at work. smile.gif

[This message has been edited by John Maragoudakis (edited 07-09-99).]

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John: I don't think help any more than the tank's suspension does when it deflect a round upward.. plus, upside down turrets have a nasty habit of sending richocets into the top hull deck.

Harold: The article you mentioned was great, not only informative, but it made all those materials classes really pay off.

Rhet: I believe that is true that chobham armor's honeycomb structure means it has to be used in flat plates. The russians are still using the more primative sandwich style composite which can be rounded.

Everyone: The article which Harold mentioned above taught a couple really neat things. First, HEAT rounds are best thought of as a cannon launched cannon. That is to say, what the heat round does when it detonated is deform the metal liner of the shaped charge into a small projectile. Its not melted, just deformed by the shockwave. This projectile isn't as heavy as an AP round, but it travels at about 4x the speed.

Second, the ceramic portion of composite armor works by applying friction to the projectile as it passes through. This effectively breaks it up. The article also mentioned that if the ceramic is constrained, it applies greater friction.. the analogy used was that if you fill both a beaker and a test tube with rice, its easier to push a pencil through the beaker's rice and harder to push one through the test tube's rice due to the contrained motion. They didn't actually say that chobham armor uses the honeycomb to constrain the ceramic's motion, but thats the conclusion I drew. Whatever it does, it must be something good to be worth giving up rounded armor for.

Chris

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