On protection of armoured vehicles

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The protection of tanks was always driven by assumptions, especially assumptions about threats. Such assumptions can be off at times, of course.

The typical armour protection up to 1938 was a mere bulletproofing. A 7.92×57 mm bullet fired from 100 m and from a position of same height should not penetrate, even if it has a core made of simple carbon steel. Such an ambition could easily be met with 15 mm normal rolled homogeneous armour steel.

An even slightly lower ambition was used for half-tracked armoured vehicles and wheeled armoured vehicles throughout the Second World War and also by many wheeled armoured vehicles in the post-WW2 period. NATO STANAG 4569 levels 1 to 3 are approximately at this protection level (level 3 is higher).

German early WW2 light tank armour layout: bulletproofing

 

This light and unambitious level of protection was very successful: The classic early Blitzkrieg campaigns of 1939…1941 used mostly this level of protection on German tanks, albeit at least frontal armour plates were usually increased to 30 mm to provide protection against anti-tank rifles as well. The German tanks that invaded and overran France in 1940 were really just bulletproofed, not shellproofed. All opposing forces’ anti-tank guns (then of 25…47 mm calibre) easily penetrated these German tanks, and so did the ubiquitous 75 mm field guns (equivalent to a 37 mm anti-tank gun in penetration) and all other artillery pieces of the day.

The downside was that tanks were often abandoned by their crews in battle when the crew noticed 25 mm shells penetrating. The morale was good enough for the crew to usually return soon if the tank did not catch fire. 

The much more extended campaign in Russia clearly called for shellproofing, considering the gazillion of Soviet artillery pieces, tanks (in 1941 mostly with 45 mm guns) and (mostly weak 45 mm) anti-tank guns faced by the German army. Shellproofing was required (first introduced briefly before the war by the British and French in heavy and not very mobile tanks), but the issue of surface area was a tough one. The more areas you shellproof, the more the tank weighs. The problem is that tanks are also supposed to drive over soft ground without sinking in too much and getting stuck. So thick, heavy steel armour could only be applied to some surface areas and the rest remained at a high bulletproofing level, proofed against 14.5 mm anti-tank guns only (~STANAG 4569 level 4).

Halftracks and wheeled armoured vehicles were never shellproofed because their smaller groudnd contact area supported less weight than tracks and they strongly tend to have larger surface areas than a tracked vehicle of equivalent payload.

The shellproofing of the turret front and upper glacis (upper side of hull front) or simply vertical hull front grew in some medium and heavy tanks to thicknesses (and angles) that could defeat 85 mm tank gun shots (with outliers protecting against 107 or 122 mm cannons on some areas) by the end of WW2.

Late WW2 German Tiger 2 armour layout: extreme shellproofing of the front

This kind of compromise was kept in the post-WW2 period: The tank would be protected against powerful shots from the front (up to frontal 60°, which includes the sides of the crew compartment) and the rest would be protected poorly, some areas not even protected against light anti-armour weapons weighing less than 3 kg such as RPG-26.

The assumption was that the tank crew could turn its turret towards powerful threats and largely avoid surprise shots from its flanks. Moreover, the hull had to be oriented at the powerful threat as well, so all that shooting on the move was super risky against powerful threats if one did something else than moving (in shallow s-lines) towards or backwards away from said threat.

So the assumptions were among others

  • a need to protect against a single known severe threat direction (roughly 60° wide)
  • a need to have all-round protection for the crew against even lightweight anti-tank weapons
  • both kinetic energy (APDS, APFSDS) and chemical energy (shaped charge, to a lesser extent HESH/HEP) threats needed to be defeated
  • both hull and turret require approximately the same protection, maybe the turret a bit more

This is not a nature’s law. Different opinions about land warfare could lead to different perceived needs, different compromises.

For example, you might assume that a tank front does rarely face another tank and its 100…125 mm gun, then you could drastically reduce your requirement to defeat kinetic threats. The armour layout would be very different with a dedicated anti-chemical energy armour scheme. Such an anti-HEAT protection could defeat a 105 mm tandem shaped charge and still provide protection against a 40 and maybe even 57 mm gun kinetic threat as a side effect. Likewise, a dedicated anti-kinetic threat armour layout would be much less effective against shaped charges than a versatile layout.

Another expectation could be that you never face threats with your side armour. Vehicles fighting only in a desert could have this expectation built in. We might see such an armour layout if the United Arab Emirates commissioned the development of a tank just for themselves.

The opposite would be the assumption that almost all shots at a tank would be surprise attacks, and maybe even shots from the front would be rather unlikely because the tank crew could react with its own firepower quickly. Then we would see an almost even all-round protection. The turret could be protected all-round against a 120 mm tank gun if the hull was armoured lightly only, but this would only fit a doctrine that assumes tanks fight in a hull down position.

top image: turret down position, lower images: hull down position

To protect the entire tank’s crew compartment all-round would restrict the protection level to protection against autocannons and moderately powerful shaped charges (calibre ~80 mm) unless active hard kill defences were employed (but those are unlikely to last for long when hit much with bullets and fragments).

So the threat assumption is two part; the technical nature of the threat and the tactical situations the tank crew will be shot at in. 

The Russian war of aggression and failed conquest against Ukraine appears to very largely ignore the old assumptions about and doctrines for land warfare in Europe. It’s more reminiscent of the Bosnian Civil War than the common 1980’s World War Three scenarios despite being fought with almost exactly the latter’s equipment.

Tanks do not appear to attack in company or battalion strength together. They fight at most in platoon strength. Tank vs tank combat is rare, and images of tanks that survived frontal large calibre hits are almost non-existing. Anti-tank missile shot videos are widely distributed and almost exclusively show shots at unaware tank crews, typically from the side (if you get to see the tank at all, as with the Stugna-P videos showing the suitcase-style user interface). The frontal armour does not protect against top attack munitions.

All in all, the Cold War era’s fixation on protection against tank guns looks foolish and inappropriate AND the fixation on the forward about 60° looks foolish as well. Moreover, secondary explosion hazards inside the crew compartment such as munitions stored in Soviet era autoloaders (but also 120 mm cartridges stored in the hull of Western tanks) looks like an intolerable design flaw.

This is all about assumptions, the layout of a T-72 makes sense within the assumptions of its designers half a century ago, and the layout of a Leopard 2 makes sense within the assumptions of its designers half a century ago. It’s just that the assumptions were maybe always wrong, and certainly do not describe what’s going on in Ukraine. They don’t describe what went on in Syria or Yemen, either. Soviet assumptions and layouts also did not prove appropriate for Iraq, either.

Soviet-style tanks are better-protected in hull down position than NATO tanks


The West has fought many small wars in the past decades, facing extremely poorly-equipped and low-skilled opposition. This did not put to full test and did not expose flaws in Western tank designs, albeit it was obvious that the assumptions from the Cold War did not describe the Iraq occupation war situation, either.

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Is it possible to quickly adapt tank design? Yes and no. The likely path is that hard kill active defence systems will be added at great costs, but their vulnerability to bullets and fragments means that they would be of little use in sustained combat. You might win a tank battle with such systems, but could not so much protect a tank through dozens of combat days with it. So again, only certain assumptions make a certain protection look like a good idea.

The addition or change of existing add-on protection is another option, but tanks have little removable armour mass (some armour inserts, some added external armour modules). To change add-on armour allows only for a slight reorientation of the protection layout.

A radical approach would be to remember that steel is fairly cheap and you could simply design a new steel hull for a different protection layout (all-round for the crew, 600 mm RHAeq CE and 200 mm RHAeq KE, all 120 mm munitions in a replaceable turret bustle under blast doors). It’s just some RHA or HHA armour plates that need to be cut and welded, after all. All the other already existing equipment such as wheels, powerpacks, sensors, electronics, tank gun, user interfaces, seats and radio could be ‘plugged in’ to this new steel shell. The might cost less than € 3 million for such a full tank makeover.

This option is extremely unlikely. It would be a major investment in a prestige object, but without adding quantity. Some quality would be added, some quality would be lost, there would be an admission that the armed bureaucracy was in error before. It’s MUCH more likely that an army would instead call for funding for an all-new tank design that would become effective for deterrence and defence only after the 2030’s. It’s hard kill APS, unofficial removal of 120 mm munitions from the hull and some added side protection in the meantime; costs € 1+ million per tank, about a ton of added weight.

Abrams tank with Trophy hard kill APS installed.
It appears to have more gadgets outside of its armour than behind it!


Likewise, we won’t hear or see admissions that the IFV concept is stupid only because it fails once again in Ukraine. The Bundeswehr’s Heer in particular will simply point that it simply stores no anti-tank guided missiles inside the Puma IFV and both 30 mm APFSDS and 30 mm AHEAD (electronic times kinda shrapnel round) have no or negligible explosives in the warhead. The 30 mm propellants will be described as insensitive and maybe the next batches of them will have less sensitive propellants and then the Bundeswehr will claim that the Puma IFV won’t blow up all the time like BMPs. That will be true, but it’s nowhere near as cheap per dismount seat, either.

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And then there’s the issue of artillery fires. 1980’s NATO’s experts believed that DPICM (bomblet) munitions would be the most serious artillery threat to tanks on a battlefield. Turret roof bomblet protection had been added to some tanks (Swedish Stridsvagn 122, for example) and also to few other AFVs (PzH 2000 SPG ad Puma IFV use the ‘hedgehog’ protection that sabotages specifically bomblets).

‘hedgehog’ add-on armour against bomblets

This old blog post /2010/08/who-says-dumb-artillery-rounds-cant.html already covered the issue that this assumption was a poor one. 152/155 mm high explosive shells are a serious threat to tanks, even without penetrations into the crew compartment. The open source intelligence on the war in Ukraine shows that armoured vehicles of all kinds get ruined by nearby explosions of such shells. A quick look at the STANAG 4569 link shows that this was to be expected for lightly and medium armoured vehicles, but near misses also mess up (up to cook off) main battle tans in Ukraine as well. Students of military history should not be surprised by the accurate targeting of individual tanks by the Ukrainians; I remember a report about how the first few long-barrelled Panzer IV in North Africa 1942 were routinely and quickly targeted by hostile artillery because their new powerful gun was such a grave threat to the Commonwealth forces there.

Bomblet submunitions are extremely rarely shown in action in Ukraine war footage. I remember only one such video, and it appeared to show bomblets from a cluster bomb, not fired by artillery. Neither Russia nor Ukraine signed the cluster munitions ban, but I suspect their Cold War era cluster munitions are degraded to a point that few of those are still effective. To not sign the ban may have been more of a deterrence bluff than anything else.

So tank protection layouts should not obsess about the bomblet threat. There’s little you can do against the blast and fragmentation threat though. The tanks’ basic armour is already most that you can do about it. The issue is the vulnerability of the many external items; optronics, running gear, antennas and even the main gun barrel (even if its bore evacuator is hardened, it’s not hardened much).

Optoronics may be protected against bullets with small and where needed movable relatively thin very high quality steel plates, but this does little against the larger fragments of old school 152 mm HE shells. It does likely help more against modern 155 mm pre-formed fragment shells, though.

The best protection against such dumb 155 mm HE shells is probably to be well-camouflaged and easily concealed (behind buildings and maybe in woodland) due to small size. That’s not exactly a strong point of the large main battle tanks used by NATO.

 

Finally, there is the issue of top protection against powerful anti-tank munitions, as in Ukraine the NLAW and Javelin. I don’t see any passive or reactive armour being able to cope with that at acceptable bulk and mass. The overflight top attack of NLAW might be defeated by countermeasures to its fusing, but this is pointless, as other countermeasures would also affect the dive attack of Javelin ATGMs, some Spike ATGM versions, UAV-dropped glide bombs and diving loitering munitions: A multispectral smoke + chaff (or equivalents to chaff) combo would temporarily affect the accuracy of such an attack and a hard kill active protection system would hit the incoming munition and reduce its penetration capability below what the turret roof offers as protection. Both approaches might lead to close explosions and a showering with fragments that would endanger external equipment such as optronics and i case of open hatches also the crew. To avoid being identified as a high value target by camouflage, concealment and deception would be much more helpful.

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I actively disliked for years the fetish about tank vs. tank duels and the assumption that tank crews would fight tank crews that they’re aware of as found in Rolf Hilmes’ books, for example. By now there’s a mountain of evidence that even this German tank tech pope was very much wrong with his assumptions.

It appears that KE protection only needs to be available against calibre up to 57 mm (hypothetical 57×347mmSR APFSDS cartridge), at most up to a hypothetical 85 mm APFSDS cartridge fired from a L/70 smoothbore barrel. Likewise, hard kill active protection systems may be limited to 950 m/s warheads, excluding the >30 mm KE threats of today (which travel at 1,300…1850 m/s). This makes the realisation of an active hard kill protection system much less demanding if not practically feasible today at all.

The Russian T-14 Armata approach (also widely discussed and modelled in the West for a long time) of a small well-protected crew capsule and relatively poorly protected turret and powerpack does not convince me on protection grounds, but it may be necessary to enable enough large calibre munitions be carried without endangering the crew. A secondary explosion would still produce a total vehicle loss, so nothing more than crew survival would be gained. That’s great for the crew and its morale, but not necessarily satisfactory from a national&collective deterrence and defence perspective.

Last but not least, we should keep in mind that even the tank hull and armour scheme layout makeover that I described would need a decade in the extremely slow-moving bureaucracies and arms industries of today. This begs the question whether we expect main battle tanks to be worthwhile in the 2030’s at all, probably surrounded by ten thousands of drones and loitering munitions. Personally, I would focus on a a rather small tracked armoured personnel carrier (less than 20 tons, more like M113 than like a Boxer) with focus on protecting against bullets and fragments. Such vehicles will likely remain useful the longest. All other new armoured vehicles should be protected versions of soft-skinned wheeled vehicles that are also in use.


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