I thanked my good star that when I was drafted into the German army (1991, freshly reunified) I got to be a Leopard 1A5 electronicd and weapons systems mechanic (EloWaMech), instead of having to fight in one.
Closer on topic, that tank had an additional no-holes layer of armor in front of the actual armored turret mostly on the two sides, and in the back with much more distance. Here is a model that nevertheless shows it pretty well:
If "detonate at a distance" does not work I wonder what the function of that kind of add-on armor was, on the sides specifically?
It should have worked fine against RPG from the back because as you can see it extended quite a bit there, creating external storage space and probably providing ample room that an RPG detonating there would not have done anything to the main unit. But on the sides it was just a few centimeters of space between the additional armor layer and the main armor.
I do remember it was really good steel. We had to replace one of those armor plates, and the new ones had the holes slightly different than the tank we were working on. Getting a new hole drilled into the armor plate proved to be impossible with the drilling tools we had.
>If "detonate at a distance" does not work I wonder what the function of that kind of add-on armor was, on the sides specifically?
It depends on the shell/threat you expect to come at you. I don't know if "capped" armor piercing shells were still a concept when those tanks were built. In that case, an initial, small amount of spaced armor is designed to "decap" the shell, because the shell under the cap has significantly less armor penetrating capability.
Well written. Sad how misunderstanding the function of cage armour
makes the AT warheads more effective. Who'd want to be in a tank? An
armour guy told me they call them "iron coffins". A bit off-topic, but
wrt statistical defences and tanks - I read an old Home Guard manual
about how to stop a tank column using dinner plates. You need a few
anti-tank mines too, which look similar. One of every 200 dinner
plates covered with dirt is an actual AT mine. Infantry sweepers have
to check each one. Another in every 200 dinner plates is booby trapped
with an AP device. Infantry want to check each one really slowly and
carefully.
> Hopefully the effect is becoming obvious - by impacting the statistical armour and detonating at that point, the armour has given the RPG a free c.300+ mm of free standoff extension. The armour just amplified the threat capability by a good 20%, making life worse for you inside that vehicle.
For an APC with ~5cm of armour, pretty much any garden variety shaped charge will penetrate it with ease. If the chance of penetration is already 100% it doesn't matter if the charge is 20% stronger. But having the cage at least gives a small chance of stopping the charge from ever detonating.
Different story with tanks though, where the extra 20% could mean the difference between a badly damaged hull and the complete destruction of both tank and crew.
> Different story with tanks though, where the extra 20% could mean the difference between a badly damaged hull and the complete destruction of both tank and crew.
This kind of additional armor is usually on the rear, which is much less protected. In fact it wouldn't make sense to put them in front of a piece of armor thick enough to survive and RPG shot by itself. So in practice this extra 20% would never change anything?
It's clear that the writer is very passionate about this topic. I didn't realize that the idea was for the RPG to get stuck in the bar. I always though it was so the explosion was outside of the vehicle. This article doesn't paint a particularly good picture for the armor. Which makes me believe that the person who came up with this got a lot of good money, but the value for the soldiers isn't there.
I don't know; I get the sense that it was "Someone shoots an RPG-7 at your MRAP; you're definitely screwed. Someone shoots an RPG-7 at your MRAP with bar-armor, you're only maybe screwed"
Seems like "maybe screwed" is a big improvement over "definitely screwed"
Indeed. The author of the article came to the opposite conclusion:
> Is bar armour worth it? It depends, but broadly yes, it is cheap, simple, and adds a layer of increased protection against a common and widely proliferated threat that would otherwise be very likely to do significant damage to a vehicle, particularly lighter classes of vehicle like protected patrol and utility vehicles (MRAPs in old money) that are vastly overmatched by the threat.
> The reality of this myth is actually more significant - detonating the warhead on the bars can be at least as bad as if it had hit the defended vehicle and, in some cases, actually a worse result for the defended vehicle.
Probably from this paragraph. It confused me as well. Throughout the whole article he’s building a case for how bad the armour is, if not worse than no slat armour, then concludes the article with “well broadly, it’s probably still better”.
Aha, I think I can see how that would be confusing. My interpretation was that it had a small chance of making a bad event worse - but I assumed a regular hit would usually be lethal anyway, and you cant kill some one more dead, so whatever probability of deflection they got out of it was pretty 'free'. I think he was going into extra detail on how the weapon performed to dispel rumours, and perhaps inadvertently created one (now some people are convinced this armor is somehow out there to line a fat cats pocket!
So why are the Russians using the very specific small and flat turret-mounted type 'Javelin' cages? The article says they're not-designed for that and would be ineffective anyway and of course RPG has no top-attack (unless you're firing from a building, which as we've seen is tricky to get it to arm in time)... so why are they doing it?
You can't stop a Javelin. Its too sophisticated. If a Javelin is launched your tank is dead.
> and of course RPG has no top-attack (unless you're firing from a building, which as we've seen is tricky to get it to arm in time)
These tanks were planning to assault Kyiv. The assumption was that cheaper RPGs (such as the AT4) would be used against these tanks. The AT4 isn't designed to be used vs main-battle-tanks (AT4 has penetration of 450mm), the frontal-armor is too thick (500mm to 700mm effective frontal armor, depending on the tank, depending on the angle the attack hits from... Largely due to geometry, not physical thickness). But the "cope-cage" might be strong enough to deflect an attack against the turret (especially if the AT4 is "top down", because it was fired from an urban building).
There's many, many, many weapons of war. There are many different types of "anti-armor" weapons.
The Russians also know that the turret has the critical weakpoint of the tank: the autoloader. If the autoloader is hit, the entire tank's munitions blow up simultaneously (aka: cooks off), and everyone inside the tank dies. Protecting the turret with a "cope cage" (even if ineffective vs Javelins) to try and mitigate damage from other RPGs (AT4, RPG7, Panzerfaust 3) just makes sense.
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Javelins are the most expensive man-portable anti-tank weapon. There's relatively few of them (yes, I know USA sent thousands of Javelins, but we also sent far more simpler anti-tank weapons as well). Javelins are $170,000 per shot, and the AT4 is $1500.
The other man-portable weapon discussed, NLAWs, are like $40,000, much cheaper than a Javelin but still an incredibly sophisticated and expensive weapon.
Media ignores the cheap stuff (AT4, RPG7) because they're not really interesting. But those are probably the workhorses and the more common weapon in the battlefield.
Also in use in Ukraine presently are the Stugna-P, a domestically produced antitank weapon [1] as well as the German Panzerfaust 3 [2]. In the footage available online, the infantry are carrying a surprising quantity of all these types of weapons - It's a quirky group of antitank weapons from a bunch of different countries. There are videos circulating in Ukraine on how to use the more foreign systems. [3] [4]
Stugna-P, Javelin, and NLAW all kinda have the same properties. They're large, bulky, and filled with a LOT of explosives. They also have a guidance system: laser for Stugna-P, some kind of computer for NLAW/Javelin, so these weapons can be shot at 1000 meters to 5000 meters and still hit their targets consistently.
But since they're larger / heavier / more expensive, they are the primary-weapon of the soldier (or squad, in the case of Stugna-P). If you're equipped with one of these, your job is to kill tanks.
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Panzerfaust, AT4, RPG7 are variants of the same concept. They're more of a "sidearm" than anything. You don't really want to be facing down a tank with one. They are manually aimed and therefore only effective at 100m to 300m (depending on how good your aim is).
Because they're smaller warheads (84-caliber for the AT4, yes its a pun/joke), they're less effective at penetrating armor. So you really want to use them vs lighter vehicles, such as IFVs instead of proper tanks. If you need to use it against a tank, you should aim for a weak point, like shooting from above, or hitting the side/rear armor.
So your snipers / riflemen / machine gunners have a job, that's the 50-cal, or machine-gun. But what if they come across an enemy vehicle? Well, the AT4 / Panzerfaust are light enough to carry _WITH_ your other weapons. Its better than nothing, and light enough to be a secondary weapon.
Alternatively, maybe you're in an environment where hitting the weak top-armor is possible (ex: Urban / high-rise building in Kyiv). Giving many, many cheap AT4 weapons out to the crowd of defenders will effectively kill even main-battle-tanks, if they are attacked at the proper angles / from their weakpoints.
> Stugna-P, Javelin, and NLAW all kinda have the same properties. They're large, bulky, and filled with a LOT of explosives.
This is a very common mis-conception. These weapons don't have a lot of explosive. They instead rely on very precise application of a little explosive, through an EFP design.
If you see a Javelin or NLAW hit an inert target, it's very modest. If you see a big explosion in a demo it's because they've filled it with fuel!
Javelin is a 50 lbs weapon. Sure, some of that weight is computer and night-vision. But most of that weight difference is explosives (I assume the 2nd tandem charge in particular).
NLAW is 28lbs, somewhere in-between.
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Tandem charges (dual-explosives: first explosion disables reactive armor, second explosion penetrates the tank) basically means carrying 2x warheads with every warhead... its weight and heavy.
Each of those Javelin explosions you see is __TWO__ explosions, timed carefully to defeat Russian reactive armor. Its a sophisticated weapon for sure, but you still have to physically carry all those extra explosives somewhere.
> Javelin is a 50 lbs weapon. Sure, some of that weight is computer and night-vision. But most of that weight difference is explosives (I assume the 2nd tandem charge in particular).
No most of it is the motor. The entire warhead of Javelin weight just 8.4 kg. That's the entire warhead - not just the explosive. An EFP contains a lot of 'inert' metal that gets formed into a projectile.
(Can we not use pounds in a technical military discussion, lol.)
I think that out of all the weapons only the javelin strikes from the top of the tank while flying over it, everything else is a direct fire missile that will hit the tank from the side.
So a 'cage device' on top of the turret seems to be intended solely for Javelins, since every other weapon simply won't strike from that direction.
NLAW also strikes from the top, just not exactly like the Javelin.
The latter does that by having a steep trajectory. The NLAW just flies horizontally over the tank, then fires down vertically. It also has the other mode where it just hits directly head on.
> everything else is a direct fire missile that will hit the tank from the side
Kyiv has skyscrapers. A dumb RPG (AT4 or RPG7) fired from the 5th story of a building will hit from the top down... onto the weaker top-armor of a tank.
Javelin rockets are $80k-$100k a piece, $170k figure is the launcher and the rocket together. Unlike NLAW the launcher is reusable (and even useful on its own because the targeting unit is detachable and has thermal vision)
That's a good point. Just like the best tool to use is the one you have at the time, mobile infantry would be more than likely to have AT4s only. I vaguely remember a section of 9-12 men would carry only two AT4 equivalents, and we were supposed to use both against the same target.
Once the tanks get bogged down, then anti-tank platoons would be deployed with the heavier gear.
nitpick--The AT4 is a recoil-less round with the propelling charge in the launch tube--not a Rocket-Propelled Grenade. I imaging firing one from inside a building would be a regrettable decision.
Those aren't javelin cages, they're called "cope cages"[1], because they're just a psychological coping mechanism for the troops inside, but offer no protection against modern smart munitions like NLAW or Javelin.
They're a relic since Russia's war in Chechnya where those cages could protect against ancient RPGs fired from buildings in narrow city streets.
> They're a relic since Russia's war in Chechnya where those cages could protect against RPGs fired from buildings in narrow city streets.
USA sent IIRC 3x as many "dumb" RPGs (the AT4) as Javelins, assuming that the Ukrainians would be fighting in narrow city streets.
Turned out that urban warfare didn't really happen much. But... I think everyone's plan was for urban combat, and then everybody turned out to be wrong. On the USA side, not a big deal, we sent the wrong mix of weapons but we're fixing that with lend-lease / additional aid packages.
> Turned out that urban warfare didn't really happen much
The war isn't really past tense; the swift advance to and battle for Kyiv with the intent of forcing capitulation didn't happen, but as the shift to seizing territory Russia really wants rather than getting handed it by a friendly government imposed on Ukraine has happened, urban warfare has become a thing in Mariupol, and if Russia continues prosecuting the war it’ll probably happen more places.
The slat armor is also only effective against the RPG-7 type warheads, where the fuse is in the nose and crushing the side of the warhead keeps the electric detonation signal from getting to the detonator.
Other warheads will detonate when they hit the slat armor. With the net result of improved standoff distance. Most warheads don't incorporate enough stand off because it's hard to do so. The extra standoff actually improves penetration.
That said, the AT4 is perfectly usable for side shots, such as in an ambush.
Hitting an enemy fuel truck from 5000m away is a lot safer than running up and shooting it at 200m.
200m shots are common in a city, because cover / concealment is everywhere. Sure, there are still trees and hills to hide in the countryside, but having the option for super long range really helps.
Perhaps it is pedantic, but in case someone reads your comment and doesn't click on the image, the name "cope cage" is a meme based around making fun of them. I think these things don't have convenient a real name because they are improvised. "Improvised top attack armor" or something like that is probably what a journalist would call them. And they probably won't get a real name because they apparently they basically suck.
>They're a relic since Russia's war in Chechnya where those cages could protect against ancient RPGs fired from buildings in narrow city streets.
Actually even in 1945 facing Panzerfausts in European cities Soviet tankists tried to similarly bolt/weld onto the top of the turret the spring metal bed frames. It didn't work well if any. While at the same time it showed the precise position of the tank while in bushes, far in the field/etc. Ukrainians have been joking about those "chicken coops" showing the tank position as another sign of a Russian fail and lack of thinking through in this war.
I'm quite interested about military technology like this, are there any good books or resources HN would recommend to learn more about anything from engineering to tactics?
In addition to military history visualized (mentioned by another commenter), I recommend:
* The Chieftain: https://www.youtube.com/c/TheChieftainsHatch . He has a series on the development of Armored doctrine for various nations prior to WW2 which is a very interesting dive into what military doctrine is and how it is formed.
* Battle Order https://www.youtube.com/c/BattleOrder covers how troops are organized and divided into squads/platoons/companies/battalions/etc in various countries and at various times.
* For getting the perspective of national security experts dealing with current events, I would take a look at https://warontherocks.com , which has a mix of articles and associated podcasts. The war on the rocks podcast has been doing weekly updates on the state of the war in Ukraine with Michael Kofman, director for the Russia Studies Program at CNA. I've found those very informative.
* Arms Control Wonk (https://www.armscontrolwonk.com/ ) the blog and podcast are interesting for looking at the military from the point of view of strategic stability.
* https://acoup.blog/ is run by a professor of military history. He covers a variety of topics; he does several series analyzing the historical realism of video games and movies for example. But he also discusses some of the fundamentals of military theory, and tends to focus a lot on what the popular imagination gets right and wrong about the military and warfare throughout the ages.
* There are think tanks like the RAND corporation, CSIS, and CNA that publish papers on a variety of topics in military theory and policy. With a little effort, a lot of them are fairly readable to the layman
* For the deepest dive, the US Army field manuals are publicly available if you search around. Skimming through them gave me a much better understanding of how an officer goes about planning an attack, preparing a defense, setting up an ambush, etc.
If youre interested in the organization and operations aspect, especially of russia and other warsaw pact countries, check out lester grau. I recently read over https://www.armyupress.army.mil/Portals/7/Hot%20Spots/Docume... as a refresher. His translations of USSR after actions in afghanistan were also worthwhile in the past.
openasocket has made good suggestions in a sibling comment. I would add that one thing that can be illuminating is works by professionals (whether current or past) recommending new directions; reading about arguments for paths not (or not yet) taken can provide a broader perspective.
(It's been a while since I’ve spent time with this; one which I remember finding interesting was Breaking the Phalanx: A New Design for Land Power in the 21st Century. [0])
Haven't seen this channel recommended yet, so checkout Perun.
I found him through the youtube algo, used to be a gaming youtuber but seems to have a day job in defense and started talking about the Ukrainian war. Hour long data dense powerpoints about what's going on over there. Easily my favorite source.
If you are interested in the field, almost everything written by Richard M. Ogorkiewicz will be a worthwhile read. He was THE go-to compiler of military engineering information in the 80s and 90s.
While the technologies he describes are a bit dated, his presentation is very comprehensive. Only problem is that many of his works are out of print.
The thing that is really dooming Russian armor in Ukraine isn't really the ATGMs and RPGs being deployed, it's the complete lack of functional thermal gear. Other than IR spotlights on most of the tanks I've seen, they're lacking in the high quality thermal sights found on most Western tanks and IFVs. If they use the IR spotlight, it's like shining a flashlight in a dark room. Everyone knows exactly where you are...
This means two things. First the UA owns the night to a large extent. This gives their SOF and TDF troops the ability to hunt the Russian vehicles at night and survive the encounters. It also helps them during the daytime as well; thermal sites are very handy in low light conditions. A hot tank engine stands out a long ways to a thermal site.
Even the Javelin CLU used by the UA has incredible thermal sites. This give troops armed with it much better situational awareness. I believe the NLAW has a good thermal sight as well, but it's disposable.
Multiplying the saved cost by probability of a defeat (which is ineffective mentioned by writer) does not seem bad considering the grid is low-cost design.
But placing timer/accelerator in RPG as a backup plan for fusing in case the warhead is shortcircuited also seems low-cost. I must be missing something here.
I'm wondering why tank armor is (appears to be) basically flat, when the AT warheads appear to be based on creating that super-heated jet, optimized for striking a flat surface?
Why not stack a few layers of corrugated steel/ceramic plates to try to split the jet apart?
Basic theory would be to present the projectile with a surface that has drastically different amounts of resistance across the front of the projectile, in the hope of destabilizing it & the jet it creates.
I guess it would make the armor quite thick, but with varying density/composition it may not end up that much heavier?
You basically invented composite armour, which is a thing already, and actually somewhat outdated.
The problem is that at such high velocities, during the impact everything acts like a fluid. Tensile strength and shape is almost irrelevant. You can think of the atoms in the armour not as a solid but as individual particles just hanging in space. Their mass — and hence inertia — is more important than anything else!
Modern armour design is about trying to have moving components that present “fresh” volume/mass to increase the effective thickness. Either via rubber layers that can distort, moving steel plates, or explosive reactive armour that do the same thing but faster.
> Statistical armour is exclusively for defeat of shaped charge munitions using a double-skinned nose as conductive path for a piezoelectric-based fuzing system.
Is there a reason for this to be a common design for RPGs? If it turns out everyone is using statistical armor, shouldn't RPG designers "catch up" by redesigning them to trigger when any part of the tip is collapsed, instead of just the tip, thus defeating this entire category of defense?
A piezo based fuse in the nose is an easy way to construct the fuse. It's also easy to construct a safety for it: stick a cap to protect the piezo from getting hit.
That said, the safety cap doesn't help if you accidentally trip and fall after taking the cap off. Most western single use AT designs use a different safety that deactivates on firing.
Not really, everybody has known that tanks on their own, unsupported by infantry are incredibly vulnerable to anti-tank missiles since, at least the Yom Kippur War (50 years ago) probably longer. The Russians for various reasons didn't and the results were predictable. So no MBTs aren't obsolete they just are very easy to break if you use them wrong.
Also there are newer active protection systems that can defeat missiles like the ones being used, the Russian tanks in the invasion either don't have them or don't have the ones that can detect threats from above.
Re: Yom Kippor in the south is where Egyptian anti tank misses did shocking damage to Israeli tanks which caused a lot of people to predict the imminent death of the MBT 50 years ago.
The Russian active protection system is called Arena [1]
Looks like a very selective view of the Yom Kippur war given what has happened on the Syrian front and the subsequent development of Israel's own MBT. Can you please share some references to "caused lot of people to predict the imminent death of the MBT 50 years ago" ?
Well, what would an MBT be replaced with? You'll still need a vehicle carrying heavy weapons to take out bunkers, enemy vehicles, etc. Maybe you can have an ATGM carrier with a bunch of missiles. But missiles are expensive, so maybe if you fit a specialized fire control system to a gun you can get the same accuracy as a missile but cheaper. That's going to be heavy, so you'll probably want tracks to spread the weight[0]. Then you'll want to protect your big and heavy vehicle too so it can't be killed by say someone with a common RPG-7. And now what do you have? A tank.
Certainly things are going to change in the future. Active protection systems (APSs) are going to be basically required, and I wouldn't be surprised if APSs became the main armor. After WWII the effectiveness of HEAT made designers believe armor was ineffective, so many post-war designs sacrificed armor for speed, such as the Leopard 1, so something similar could happen again.
But an important part of the equation is tactics. A very similar question to "why do we still need MBTs" is "why do we still need infantry" and the answer is the same: they synergise[1]. Infantry need tanks to blow up hard points, and tanks need infantry to keep an eye on the surroundings, suppress and occupy potential firing points, take buildings to prevent them from being used to fire ATGMs and to use to look out for enemy ATGMs, etc. Infantry itself doesn't do anything to reduce the threat of missiles, but infantry-tank coordination tactics do.
[0] For example, the Stryker MGS is a wheeled vehicle carrying a gun. It's widely regarded to suck badly, but in principle there's no reason you couldn't have a good wheeled gun carrier.
[1] Also you need infantry to go places tanks can't go and root out defenders, plus actually do the work of holding enemy territory like talking to local leaders, clearing the radio station of hostile DJs, etc
Shtora is really not an APS. It's more of a countermeasure system designed to fool the laser guidance used by missiles etc. Think of it like ECM for a tank.
APS is more along the lines of Trophy (Israeli and eventually US), or Drozd/Arena (RU) where radar senses projectiles, and fires counter projectiles at the incoming round/missile.
Drozd was never really implemented; partially due to cost, but also because it tended to kill any infantry accompanying the tanks. Arena appears to be much of the same tech, focused on RPG type weapons as well as ATGMs. I think the reason we don't see much of it on the Russian tanks is again, cost. The export version was pitched to South Korea at $300k per unit. And compared to the cost of a T-72B3, that's a significant amount to add. Or it could be the typical Russian military corruption we've been seeing in Ukraine.
I think you are confusing APS systems in general (of which Shtora is one) and the subset of APS systems that are hard-kill such as Trophy.
Of course regardless of efficiency, an APS system has to be installed in the first place and it is possible that that is not the common case in Ukraine.
APS generally refers to hard-kill systems like Trophy/Arena. Things that actively go kill the missile or projectile coming towards the fighting vehicle. Shtora is not active, it simply disrupts the laser guidance (if it can detect the beam in time). It's no different than an ECM jammer on a fighter or surface ship.
For taking out hard targets: precision artillery firing guided munitions from further behind the front lines, with minimal armor but protected by APS, and highly mobile to shoot and scoot?
Both the US and Germany bought Trophy, the Dutch bought Iron Fist (another Israeli APS), a few other NATO members are evaluating Trophy and also working on their own APS.
So MBTs are going no where, APS would become more common and more important and the doctrine of now not having your tanks alone without infantry and ISR proving support would be even more solidified.
Both are advertised as being effective against high elevation threats, both Trophy and Iron Fist have been tested against missiles launched from helicopters when during their acceptance testing by the Israelis.
Trophy has a +- 38 degrees of elevation firing, Iron Fist can do -40-+60.
At least against something like an NLAW that flys above the tank both would have a firing solution.
The US when evaluating the system for both the Bradley and the Abrams tested it against the Javelin and other modern anti tank threats.
As far as non-western weapon go Trophy has intercepted fairly modern ATGMs like the Russian Kornet-E and it’s licensed Iranian clones which also employ a top-attack attack profile.
I'm guessing we're going to see more active protection [1] that tries to detonate incoming projectiles at a distance to nullify the effectiveness of shaped charges.
Good lord.. While I know about existence of APS especially on Merkava tanks, this video really shows how modern warfare can brush right up against science fiction.
We're able to detect an incoming round and automatically kill it with a directed explosion, all faster than you can blink. What, are we going to see munitions that has submunitions of its own to counter the countermeasure next? (That might be a reasonable development actually)
Either way I'm fortunate that these things aren't used around me, and I'm not in any danger. I would love to one day see those C-beams glitter, as a spectator in safety
> Either way I'm fortunate that these things aren't used around me, and I'm not in any danger.
At the 2m20s mark, they claim this leaves personnel 10m away unharmed. So, it seems you can watch from quite nearby. You’d have to avoid being hit by the incoming stuff, though, and I guess wearing hearing protection is strongly advised, too.
As to countermeasures, I would guess this doesn’t work well against kinetic energy projectiles that don’t explode but depend on mass and velocity to do damage. Or would it?
Tanks have always been vulnerable to cheaper weapons, whether that's an anti-tank gun hidden in rubble or a NLAW. This is why tanks require infantry support---to locate and deal with those threats while the tanks deal with things the infantry cannot.
Many of the videos from Ukraine have been ambushes (sort of a separate matter) or of AFVs operating without close infantry support. That's not a good way to do things.
Closer on topic, that tank had an additional no-holes layer of armor in front of the actual armored turret mostly on the two sides, and in the back with much more distance. Here is a model that nevertheless shows it pretty well:
https://www.super-hobby.at/zdjecia/0/7/3/35478_rev03320-4.jp...
If "detonate at a distance" does not work I wonder what the function of that kind of add-on armor was, on the sides specifically?
It should have worked fine against RPG from the back because as you can see it extended quite a bit there, creating external storage space and probably providing ample room that an RPG detonating there would not have done anything to the main unit. But on the sides it was just a few centimeters of space between the additional armor layer and the main armor.
I do remember it was really good steel. We had to replace one of those armor plates, and the new ones had the holes slightly different than the tank we were working on. Getting a new hole drilled into the armor plate proved to be impossible with the drilling tools we had.