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Suppose in the future tanks are able mount higher velocity guns such as railguns or electro chemical technology (ETC) guns. Suppose these tanks slightly larger normal (no you can't mount a railgun on an M60). These cannon rounds are going to make mincemeat out of most armor systems, especially as they go beyond the prototype and first deployment phase. Simply slapping thicker armor isn't going to work eventually. Suppose we have these rounds being slung at us fragile humans inside our big metal tanks. In terms of the survival onion we are at the Don't get penetrated phase.

As a tank crewman, how do we survive. What active and passive defense systems could be employed so that we aren't turned into ground meat. Replacing the tanks with AI or remote control is off the table. Unlike missiles these kinetic weapons are coming incredibly fast but are unguided.

Time frame wise imagine that we have sufficient enough technology to mount a railgun on something slightly larger than the size of an M109 Paladin or M1A2 Abrams. The ETC guns are in a similar vein but aren't weighing down a tank as much.

Edit: Current tank rounds travel at around 1.8 km/s/. For ETC guns, if we're being semi realistic. Then around 4km/s or slightly more as the upper end.

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    $\begingroup$ Title and body are asking two different things. And it would help if you put some numbers to help us give an answer. Up until c there are a lot of possible velocities. $\endgroup$
    – L.Dutch
    Jan 27 at 8:23
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    $\begingroup$ Wouldn't Electro Chemical Technology be ECT not ETC? $\endgroup$ Jan 27 at 21:14
  • $\begingroup$ We're already on the don't be on the business end of it with conventional weapons. I'm unaware of there being anti-anti-tank rounds. Same problem with ballistic missiles; they're un-interceptable. Unless you got lasers in a 747 but I think we scrapped that project. $\endgroup$
    – Mazura
    Jan 27 at 23:38

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I assume for this question that you specifically want a human crew to do everything in a WWII feel rather than the more modern hunter-killer idea where both gunner an commander can identify a target and a computer aims the gun & elevation for the shot while the commander and gunner find the next target. For that reason:

  • electronic warfare, lots and lots of electronic warfare.

The current complexity of electronic warfare is already high, with bouncing, ever changing signals that have to be both specific and random to prevent interception or to ensure that you seem somewhere else. Just like today you don't really talk about it, just say that the onboard computers still have problems identifying targets due to all the electronic warfare that has come out. From realistic false IR/Radio signatures to false shapes and lasers that blind cameras meant to identify the shape of objects and stealth materials, all reduce the effectiveness of computers and increase the necessity of humans at the wheel.

  • first defense: don't get hit.

This is the cheeky one and likely what you will be completely buried in. Stealth, camouflage and speed would be key components to avoiding getting accurately shot at. The MBT design is actually partially based on this, as its speed needs to be high enough to avoid getting hit while crossing the distance to an enemy position.

  • second defense: whipple shield.

https://en.m.wikipedia.org/wiki/Whipple_shield

At high velocity impacts metals start acting like liquids. A whipple shield is used on space objects against high velocity impacts. The outer shield isn't designed to stop the projectile but to break it up so that the projectile spreads out over a larger surface area beneath the whipple shield. For your large and more designed high velocity projectiles your whipple shield will likely see some adaptations, like Explosive Reactive armor additions, more dense filling, thicker outer whipple shield etc.

  • third defense: active defense system

This might be a harder sell due to the electronic warfare present, but an advanced active protection system could identify the projectile and fire its own projectile at it. At such high velocities you won't be changing the projectile's path much but you would essentially use the APS as an early whipple shield: the projectile is damaged or broken up and no longer flying tip-first into your tank.

  • Fourth defense: metamaterials

You've got the future tech of high velocity projectiles, so why not some metamaterials? Synthetic spiderthread can be much stronger than even the strongest natural spiderthread, mass-producing that would help create many strong materials to intercept a projectile before it enters the crew compartment. Graphene and other molecularly perfect metamaterials at bulk production could offer an immense increase in the amount of armor available.

Diamene (https://www.google.com/amp/s/www.graphene-info.com/new-graphene-material-called-diamene-switches-flexible-harder-diamond-upon-impact%3famp), a form of Graphene with two layers of graphene on top of each other, could be mass produced with a third layer of another material at one end. That would mean you could start stacking diamene. A back of the envelope low estimate calculation would let you place 7250 layers of diamene per centimeter of armor, which would likely be a good boost to your armor. Pure Graphene layers would be 28.785 layers of Graphene per centimeter. Many such technologies together could help give the armor enough strength and still lightness to handle high velocity impacts.

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  • $\begingroup$ Actually I don't mind the automation of modern tank combat. There's definitely a lot of computer assisted systems in modern tanks. I'm totally fine with the having a computer handle plotting an intercept course or guiding a weapon to counter the enemy round. The reason I put the no AI/remote control is that usually I tend to get the whole "just remove people, problem solved." answer. While valid in reality, it just takes away the whole character aspect from a story. $\endgroup$
    – FIRES_ICE
    Jan 27 at 12:03
  • $\begingroup$ Your active defense system could be a laser - it's easier to hit a a fast target with a laser than a bullet, and even if all you do is heat it up a little, that should make the Whipple shield more effective. $\endgroup$
    – codeMonkey
    Jan 27 at 19:42
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    $\begingroup$ Don't get hit. Fullstop. Do not pass go. Do not collect $200. $\endgroup$
    – Mazura
    Jan 27 at 23:49
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There are a number of ways to defend against a 4+km/s long-rod penetrator (LRP), which is the most likely warhead to be fired from such a high velocity gun.

  1. Active armour: By having the outer layer of armour seperate to the bulk of the armour, and on impact, propelling it sideways with high explosives, the projectile can effectively be made to penetrate a greater thickness of armour, and the lateral motion of the moving armour slab applies a torque to the projectile which makes it turn and effectively impact the armour side-on. As Newton's Impact Depth Approximation relies on a LRP to be long to penetrate thick armour, making the LRP impact mostly side-on makes it effectively very much shorter and very much less penetrating.

  2. An emphasis on operating hull-down: Modern tanks have their crew in both the hull and the turret. A hit to either the tank's body or turret may result in fragments bouncing around inside the tank and causing crew injuries, due to the relatively large opening between body and turret. If the size of the turret ring was minimised by moving all crew into the body, and light armour was placed between the turret and body, then hits to the turret might disable the tank's weapons, but would be less likely to injure the crew. By emphasizing operating hull-down, protecting the tank's body by only exposing the turret to the enemy above crests in the landscape, most hits will occur to the turret. For the body to be hit would mean that a tactical error had been made.

  3. Each crew position should be compartmentalized and seperated from one-another by armour and light energy absorbing materials. While a direct hit may kill one crew member, unless the shot is also aligned with another crew member, this internal baffling should catch any spall and protect the crew from injury in the event of a penetrating hit.

  4. Emphasis on remote operation and automation: By loading and aiming the turreted main weapon remotely, it can be made smaller, and present a smaller target silhouette. Additionally, by separating the crew and having them perform other functions by wire rather than by viewports, fewer vulnerable points are created in the hull. By requiring fewer crew, the tank's body can be made smaller, and due to the square-cube law, the armour can be made thicker without adding as much weight.

  5. Emphasis on smaller crew members: By requiring the necessary crew members to be physically small, less space need be allocated to them, also allowing the vehicle to be smaller and more readily armoured.

  6. Greater armour slope: By making the vehicle as low as possible, and making the main armour sloped at as great an angle as possible, the flatter trajectory of higher-velocity shots means that deflection of the shot is more likely. Of course, even if the shot is deflected, there may still be spalling, but less energy will be delivered to the vehicle, and spalling is easier to mitigate.

It might seem logical that the higher the impact velocity, the higher the penetration, but once velocity gets high enough, both projectile and armour begin to behave as if they were liquids. Newton's Impact Depth Approximation shows that the impact depth is proportional to the length and density of the projectile vs the density of the armour. If densities are equal, impact depth is approximately the same as projectile length. So, the battle between projectile and armour boils down to density vs density and length vs thickness. However, transmitted energy is still a factor. Armor might stop or deflect the projectile, but the transmitted energy might still cause spalling. Computer or real-world modelling would be required.

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    $\begingroup$ There are two problems with the approach: 1 - active/reactive armour is of limited use against kinetic penetrator. 2. with increasing velocity to 4km/s you're basically increase the kinetic energy by almost an order of magnitude (i.e. M829A4 produces 11 MJ of kinetic energy on impact with 1530 m/s end velocity, penetrating maybe 1000mm of RHA, with 4 km/s it is 80MJ of energy, which would be at this point KEW). Penetration is then easy and then explosion won't be significantly mitigated by compartmentalization. OP is correct, in this scenario enemy hit is an instant kill. $\endgroup$
    – AcePL
    Jan 27 at 10:37
  • $\begingroup$ So like, just how they are, except it's coming at you at 4km/s instead of 2. That it was electrically propelled doesn't change anything. If you double the speed of a slug, what multiplier do you have to apply to the armor? Times two? Or more like times 4? $\endgroup$
    – Mazura
    Jan 27 at 23:45
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    $\begingroup$ @Mazura Actually, no. Newton's Impact Depth Approximation shows that once the velocities are high enough, the armour and projectile act as if they were liquids. Impact depth at high velocity is independent of the actual speed. Energy delivered is another matter... Computer modelling would likely be required. $\endgroup$
    – Monty Wild
    Jan 28 at 0:01
  • $\begingroup$ @AcePL 1: CURRENT active defenses are of little use against kinetic penetrators because they react too slow. However if you have a fast-reacting one you can break/shatter/tumble the projectile, which would instantly remove a tremendous portion of what makes it lethal (a long rod hitting with all its weight at one spot and not spreading out). 2: sometimes more speed is not as good. A bullet at bullet velocities would make it to the other side of a whipple shield intact and be able to deal more damage than at orbital velocities where it breaks up under its own pressure at impact. $\endgroup$
    – Demigan
    Jan 29 at 9:14
  • $\begingroup$ @Demigan - Actually, they aren't too slow. Kontakt-5 was designed to defeat sabot rounds and was quite successful. But not all of them, and newer APFSDS are designed specifically to defeat ERA and then armor with little to none difficulty. And I don't think you quite grasp the concept of kinetic energy. Bullet at orbital speeds is basically a micrometeorite, regardless if it breaks up at impact or not, as it has still tremendous energy... Grain of sand at speed of light is equivalent to a multi-megaton nuclear device. That is why it's called kinetic energy weapons... $\endgroup$
    – AcePL
    Feb 1 at 8:43
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What you're describing is basically how the APFSDS-T (also called, among other things, a sabot)projectiles work. They are sub-caliber projectiles, made from very dense and heavy material (depleted uranium, tungsten etc), which travel at high velocities to achieve kinetic kill.

Current variants do reach 1.8 km/s, as you mentioned. This allows them to achieve successful penetration of (at minimum) 850mm of RHA armor. That is a lot, but new ones, entering service now, have much more penetration. How much is yet unknown - numbers are unavailable. But they do it in one of two ways: increase velocity at the moment of strike and/or increase mass of the penetrator.

There are in development new types, where the increase is in speed. It is estimated that with all other factors staying the same, increase of velocity from current 1.6 km/s-1.8 km/s to desired 2 km/s adds a bit over 10% to penetration values. Though it may require different material of the penetrator. There's a reason why US is sticking with depleted uranium penetrator - where velocity is actually lowered, but mass is doubled, and ERA-defeating capabilities have been added... It has been found that there is a point where too fast is actually a thing.

So, if you plan to go up to 4 km/s of penetrator velocity, it means that this projectile will have anything between 2x and 10x increased lethality compared to defenders. Depending on the end of that scale it will at be at least enough or way more than enough, then. For example, latest US APFSDS produce on impact almost 11MJ of kinetic energy from 10.5 kg penetrator at 1.65 km/s velocity. If same projectile would travel at 4 km/s, then the energy yield is just around 80MJ. For comparison, 155mm HE projectile from current-tech howitzer explodes with about 55MJ of energy (though from 10.8 kg of TNT explosion), and it has been demonstrated that it will basically crush an M1 Abrams tank no problem. What an 80MJ kinetic penetrator does to a tank is pretty much the same, just bigger still.

Current defensive tech is basically what you described, as well: don't get hit. Of course, there are additions, like composite armor, reactive armor, shape of the armor (sloping and angling to increase chances of projectile bounce), which increase survivability - and it is worth noting that explosive reactive armor (ERA), while developed against high-explosive-anti-tank (HEAT) rounds, can be quite effective against some of the sabot penetrators (i.e. Kontakt-5 ERA uses the brittleness and rigidity of tungsten against itself, in effect shattering the penetrator and rendering it useless) but the tactics are basically shoot and scoot.

So if you look for something to increase survivability in the face of enemy with superior firepower you have two ways, one of which you already discarded (add more armor).

That leaves the other way: stealth. Make your vehicles smaller, add some stealth tech to them and basically adopt tank destroyers tactics across the board. Which is basically concentrated fire from ambush, and then retreat.

Alternatively, if enemy uses mostly kinetic-based firepower, then consider producing man-portable weapons and/or technicals in large numbers (where platform is civilian-market vehicle with added gun). Because in this case no armor is the best armor...

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Guided redirection/deflection

You might not be able to fully stop such a projectile, but you might be able to deflect it so that it either goes past you or causes less damage. Relying on passive deflection, even with the best armour designed to do so, can and will fail, so you're going to have to have some way to actively re-orient the armour to provide the least damaging/most perfect deflection on a per projectile's path basis.

If it were me I'd give each tank a 'shield arm', a powerful mechanical arm with a large, lengthy, and thick metal plate(probably made of spring steel) designed to not stop/block an incoming projectile but rather to redirect or deflect it. You can have this be guided by a soldier trained to handle the equipment, but you'd get much greater accuracy(a better angle for deflection) when you implement an AI behind the control of this arm.

Should an actual arm prove to flimsy an attachment for this(more than one joint/point of failure), you could design the hull of the tank itself to be adaptive to the path of incoming projectiles, like large scales that re-orient themselves. I personally still think an arm would be better though, as it'll give the projectile more time to be redirected and the action won't be happening so close to the tank itself(which houses your soldiers if you haven't gone the way of remote warfare)

The entire practice of a tank's deflection will be similar to how bullets can skip off of vehicles(despite most cars not having much to speak of in the way of armour), video example, but being better at the whole thing due to actual armour being in place as well as the angle being adjusted for perfect or near-perfect deflection.

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    $\begingroup$ This seems like a neat idea, but I have a hard time imagining it wouldn't be too slow. $\endgroup$ Jan 27 at 21:23
  • $\begingroup$ @coppereyecat a world where rail/coil guns can be mounted on tanks & reliably shoot projectiles at mach 8-12 probably implies huge advances in material science, so I think it's consistent w/ the premise to assume they can make the arm out of something lighter than carbon fiber & several times stronger than anything available today, & they'll already be designing the tank w/ super-capacitors to drive it. Could be physically realistic as long as it can sense & react in realtime I think $\endgroup$ Jan 28 at 8:40

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