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I have a setting where the environment is constantly changing on the ground level. As a result, hover tanks are used more often than tracked or wheeled tank destroyers/IFV/APCs. The ground can literally change from semi solid, to liquid to jagged/rocky etc in mere minutes. So simply using boats or wheeled/treaded vehicles isn't a straightforward operation.

One of the issues I have with my hover tank design is that the recoil for main guns is pretty massive. Infact they can put some serious stress on the turret basket/rings during prolonged combat operations.

I plan on using rockets, something akin to a recoilless rifle or general unguided rocket round as the hover tank's primary offensive weapon. However, one of the issue's I have is the negatives of rocket rounds. Rockets in general are slow and far less accurate compared to their shell-based counterparts. What changes would need to happen to a rocket/recoilless rifle to make them more effective/close the gap between unguided rockets and normal tank shells?

While I don't require the same velocity as tank guns, I'd like to get as close as possible as armor piercing rounds are a type of round that hover tanks would be equipped with. Normal explosive effect warheads such as high explosive anti tank or the occasional high explosive/ HE squash head are also types of munitions that I'd like to field.

One idea that I considered is to use a railgun apparatus. As in that a rocket is attached to a sabot which is in between multiple rails. An initial motor fires off, then a few moments later the rocket goes down the rails and exits the "railgun" barrel. Note that this isn't an actual railgun that uses power to launch a shell. Rather a rocket has a motor that's slowly burning up to maximum speed before it goes down the rails. Kind of like the locks on the Space Shuttle that prevent it from launching/tipping. The issue with this is accuracy.

All fired rocket rounds are unguided. The two main considerations are speed and accuracy.

Edit:

I should clarify what I mean by unguided. I don't want an active guidance system that such as MCLOS/NLOS that can change the vectors of a rocket. However, things such as fins, rollerons, simple gyroscopes etc are fine if they are being used to keep the rocket on a general path in the direction it was fired at.

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    $\begingroup$ Why do you want the rocket rounds to be unguided? A chief advantage of modern anti tank missiles is that they can be extremely precision and perform “top attacks”. $\endgroup$
    – user71781
    Oct 24, 2022 at 3:18
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    $\begingroup$ Also if you didn't know, some armies have already developed tanks that can fire guided rocket rounds via their main gun barrel, effectively usng them as another kind of ammo. $\endgroup$
    – Vesper
    Oct 24, 2022 at 7:19
  • $\begingroup$ About your railgun with unguided rockets - you have seem to reinvent the Katyusha, just on a hovertank chassis. Usable if your warring parties don't have access to missile guiding systems, and quite suitable to the environment from what I read. $\endgroup$
    – Vesper
    Oct 24, 2022 at 7:27
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    $\begingroup$ Iirc many missiles have a pretty high speed already, coupled with guidance that allows them to overcome wind, elevation and other factors. They might start slow, but continuous acceleration helps a great deal in speed. Not to mention that increasing speed with shells means exponential more stress on a gun. A rocket just needs to have more/more powerful propellant. In comparison shells are less accurate, have less variability in armament and less angles of attack. You can probably take more and in various cases are faster, but in general a rocket should be better. $\endgroup$
    – Trioxidane
    Oct 24, 2022 at 10:34
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    $\begingroup$ Beware of technologically escalating your vehicles out of a job. If your tanks get fast enough rockets to duplicate the role of direct fire artillery, presumably the infantrymen trying to kill your tanks also get them. $\endgroup$
    – g s
    Oct 24, 2022 at 21:09

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It has already happened in real life. Modern day missiles can have much longer ranges and explosive yields in comparison to artillery shells. Take naval combat for example. Naval warfare used to be dominated by huge guns, guns far larger than anything ever put onto a tank, but now naval warfare is utterly dominated by missiles. Missile interception in naval warfare exists, but as the sinking of the Moskva in the Black Sea earlier this year demonstrates; modern ships can be defeated by missiles. The ongoing Russo-Ukrainian War is further illustrative, as the Russian tank corps has been utterly decimated by anti tank missiles such as the Javelin. Russian conventional artillery was briefly giving the Russian army an edge, but the usage of the HIMARS missile launch platform and the accompanying ATCAMS missile has lead to devastating losses for the Russian Army.

These changes were brought on by advances in computer based targeting, as the javelin is a fire and forget missile that changes course mid air to perform a top attack, and the HIMARS calculates the trajectory of artillery fire to launch a devastating missile barrage.

Edit: If you are solidly against guided munitions, consider the merits of tandem charge or multi stage warheads. These warheads are designed to destroy any modern armor and consist of multiple sequential charges.

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    $\begingroup$ Politics aside, modern war is essentially missile vs missile indeed, with various stuffs that could also be called a missile (suicide drones, other kinds of drones, swarms, etc). $\endgroup$
    – Vesper
    Oct 24, 2022 at 7:24
  • $\begingroup$ Explosive effect warheads are definitely the major advantage a rocket has over something like APFSDS. However, the major problem I have with rockets is accuracy and speed. In this case most rounds will most likely be using some type of tandem charge, but hitting the target is the hard part. Especially since the tank itself can be moving rapidly. $\endgroup$
    – FIRES_ICE
    Oct 24, 2022 at 9:51
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    $\begingroup$ @FIRES_ICE rockets are much more accurate due to their ability to track target and adjust course. A shell is difficult to have correction or other electronics/propellant due to the shock of firing. At shorter distances the rocket speed will matter less as you have little time to react, while at longer distances they should increase in accuracy. Compare the slower hover to real life planes, where just because of speed and maneuverability rockets are king. Not to mention that plenty of (big) rockets can achieve much higher speeds than shells over time. $\endgroup$
    – Trioxidane
    Oct 24, 2022 at 10:42
  • $\begingroup$ @Trioxidane while MCLOS or NLOS guided rockets/missiles are effective, the rockets in this case are unguided. MCLOS and NLOS guided weapons exist in this setting, but unguided rockets are used as the ammunition for the main gun. $\endgroup$
    – FIRES_ICE
    Oct 24, 2022 at 11:40
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    $\begingroup$ @FIRES_ICE ...then don't use unguided rockets. If they can build hover tanks, they can build guided rockets. You would need an exceptionally good reason that they would build a system that does not take advantage of them. Having everyone arbitrarily ignore an obvious solution to their problems is rarely a good basis for a story. $\endgroup$ Oct 24, 2022 at 17:48
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Inertial Dampers

There is no way around your problem. Unguided missiles are inaccurate because they exit the tank slowly. This is the same reason they lack recoil. You are free to claim the missiles accelerate faster than real missiles. But I presume you want a simple reason for that.

Putting a railgun in the tank doesn't help. It makes no difference what happens inside the tank when it fires. It might be a shell. It might be a missile. It might be a catapult with a boulder. It might be Uncle Dan with the garden hose. It might be a flock of chickens taking off from the hull. Whenever something fast comes out one end of the tank, the tank is pushed back with proportional force.

Instead of ditching guns, just use your hover tech to balance the recoil. The tank has grav-plates on the bottom to push it upwards. It has plates on the front, back and sides to push it forwards and turn. Of course it does, that's how it gets where it is going.

When the gun fires, the grav plates on the opposite side of the tank flare temporarily to balance the recoil. It is not perfect but the targeting computer can predict the recoil and compensate so the shell goes where the human was aiming.

This is more exiting too when the targeting computer or balancing system gets shot off and the heroes have to aim and compensate manually. The tank crowd loves this kind of stuff. See Fury 2014 with Bradley Pittsburgh:

enter image description here

See Girl and Tank, with the same premise:

enter image description here

To lower recoil further you can use smaller shells that are either fast or contain concentrated explosives. Or you can have spikes on the bottom of the tank that stick into the ground if it is in place while firing.

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    $\begingroup$ Hm, well, rockets can impose no recoil because there is nothing pushing on the launcher, provided the launcher is side loaded and has an open back. Same reason infantry can fire rockets and not go flying backwards. The force of the rocket's takeoff is ejected from the open rear of the tube. So you could have a very fast rocket with still no recoil, provided there is some design that lets it exhaust cleanly through the tank. Perhaps with barrels on the side rather than one in the middle front. $\endgroup$
    – JamieB
    Oct 24, 2022 at 18:21
  • $\begingroup$ @JamieB Rockets are good because they can have no recoil. They are bad because they take longer to reach full speed. So unguided rockets are less accurate than shells. $\endgroup$
    – Daron
    Oct 24, 2022 at 20:27
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I think it could work. You just need one hell of a rocket propellant. I don't know the formulas for that, but I feel like it's at least within the handwavium "it's possible" realm. (Google research task: how fast is a tank shell. How fast is the fastest rocket. How fast do rockets accelerate to maximum speed.)

But the key to keeping the tank from having recoil would be to put the launchers on the side of the tank. Maybe a left and right barrel rather than a central one. They are loaded from the side, with an open back. Rocket goes in, rocket fires, exhaust comes out the back and the tank should experience close to no force at all -- the rocket is entirely disconnected from the tank. (If you put the rocket in a standard central tank barrel then the back-blast of the rocket would hit the tank, much like a shell, and you'd then have to deal with all that force.)

This wouldn't work with shells, I don't think, since I believe the back-blast is a key component of giving the shell maximum oopmh.

Then the question is really "how fast can we make a rocket go, especially with absolutely maximum acceleration".

But additionally, you really just want the speed for the sake of accuracy against moving targets. The actual lethality of modern rounds does not rely so much on the speed of the projectile, because the projectile itself is an explosive, armor-piercing warhead that can (and is) literally dropped from a drone and can still kill a tank. Or see also: anti-tank mines. Big enough boom and you don't need speed, except to help guarantee a hit.

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Spray and pray

Lets assume the requirement of the unguided rockets. Between a cannon and rockets, the rockets are much more versatile, devastating and accurate.

Lets start with the accuracy. As you say the hover tank is moved more easily by a cannon. This makes the tank immediately less accurate. It moves backwards compared to the barrel, but depending on how it's mounted it'll also tilt the whole platform.this changes the trajectory of the shell, as it is both moved and the barrel exit isn't pointed at the right location any more.

A rocket in comparison is much more benign, as the rocket doesn't use all it's propellant to push off the tank, nor does so all at once. At the speeds they travel the difference between a cannon or a rocket can be minor. It can even be in the advantage of the rockets if the engineers try to make more accurate cannons.

This comparatively benign fire allows for rocket pods. You can fire a ton of rockets all at once! On hover tanks that aren't hunkered down accuracy will still be a problem, but with some software compensation you can still hoze down a huge area with some accuracy. Why try to fire once and hope to hit if you can immediately take down one or multiple enemies in seconds? Regardless how they move they can't evade a barrage in a tight cone around them. Though evade is a misnomer with how fast rockets are going on many distances. It is more a question of missing than evasion.

If the higher chance to kill in a shorter time isn't enough we can look at armament. Rockets are more versatile in their payload. You can do any strike that a shell has with a rocket and more. Different explosives, fuel bombs, napalm, gasses and aerosols and even some electronics can all be transported by rockets. Maybe spread an aerosol that disables the hover. Or poison the crew. Or ram through several layers of armour to make metal spread at lethal speeds through the cockpit. The point is you have options.

To me unguided rockets on a hover tank are more accurate, can be fired faster in many modes and has the ability to have a large difference in armaments. If you can temporarily fix the hover tank in place the accuracy will go up wile still able to hoze down an area.

The only flaw is that you are more likely to go through rockets at a higher pace than shells. But this is a choice. If you want more effectiveness you would install guided missiles. These groups clearly have enough resources to just pump out a ton of unguided rockets and use these to spray areas for quick effects.

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Whilst it's true that a railgun imparts the same inertial impulse as a charged ordinance, it lacks the initial explosive force, but rather spreads the acceleration evenly over the length of the rail.

This results in lower stress on the mountings and the vehicle as a whole.

It's also potentially more controllable, so that you precisely match the force applied to the slug with the anti recoil force exerted by the tank's drive system.

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A rocket you can use beats a gun you can't use, no matter how superior the gun's theoretical statistics might be.

What matters here is the entire weapon system and the way it interacts with the environment, not just comparing numerical statistics.

If there are three armies, one with rocket-armed hover-tanks, one with gun-armed hover-tanks, and one with real-world tanks, which one actually performs best in the world you're creating?

You've already told us that the ground is too unstable/unpredictable for tracks, so real-world tanks are out. That means that main gun performance as observed on real-world tanks doesn't matter anymore. Your rocket tanks don't need to be capable of out-shooting something with that performance envelope, they can just play keep-away for five minutes and then watch their opponents sink.

So the next question is what the accuracy of the gun might be when on a hovering gun platform. Recoil is likely to play hell with the gun's theoretical accuracy advantage once you pull it off the ground - enough that it's entirely plausible that rockets are actually the more accurate weapon on these tanks. If you want to, you can lean into this further: the hover-tech being used causes unavoidable vibrations or rolling, so for accurate aiming the weapons need to be mounted in a gyroscopically stabilised turret, but the mounting system that isolates the turret from the motion of the main body simply can't handle the recoil from a cannon.

This is a world where tank combat is short-ranged and drawn-out relative to our modern world, as the weapons available simply aren't as accurate (and therefore lethal) on a single long-range shot, but that's not inherently a problem. There's a decent argument to be made that the 'first shot wins' dynamic makes for a less interesting story anyway.

If you go with this explanation, you do still need to consider what the role of heavy guns might be outside of tank weapons.

Maybe this world just hasn't pushed technological development of guns relative to rockets so it's not an issue (we can't put it on a tank, so it doesn't get a research grant).

Or maybe having a small number of weapons that can out-shoot standard tank armament is something you just want to roll with. If major strongholds are the only places that can put down a stable platform for guns (and the guns are significantly more accurate than rockets), then you've just created a big advantage for defenders who have proper fortifications - but that's not necessarily a bad thing, depending on your story.

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You should take a look at missiles like LOSAT. They have similar firepower to tank guns from a truck chassis, relying purely on kinetic energy rather than warheads. The success of top attack like Javelin or Hellfire made them currently unnecessary, but with active protection systems coming online something similar may be developed again because their engagement time is so much shorter APS might fail.

Unguided rockets are inherently a problem, because they are much less accurate than tube fired weapons. Without the ability to fire from the long barrel of a cannon, you just can't get the same level of accuracy with an unguided rocket regardless of how much you try and add precision components. If you're going to the trouble to put in passive stabalization systems, you might as well just make it guided. At this point even rocket pods are getting laser designators. What exactly is the reason you want unguided missiles in the first place?

MLRS vs tube artillery shows the other flaw with missiles. An MLRS rocket costs $150,000, while unguided artillery rounds can be as low as several hundred dollars. Would you rather have a single missile or 200 shells? This is also another reason tanks are valuable, as their cannons are cheaper than the missiles that would otherwise have to be used instead. If you rely on unguided rockets they are for grid squares rather than specific targets, which doesn't really work all that well in a tank battle outside of extremely close range.

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