"125mm tank cannons: as big as they will ever get?" Topic

Just some musing here, but do you think that MBT main guns have hit their ceiling at 120mm for manual loading and 125mm for autoloaders?

My hypothesis is yes. I don't think that a crew loaded weapon could be any larger than 120mm and still have the rate of fire and ammo supply needed for a modern MBT. Even if the west adopts autoloaders I cannot see them being bigger than 125mm (maybe 130mm but I think that really is a hard ceiling for MBTs).

Why? it comes down to weight. A bigger gun means heavier tank, which means a bigger engine is needed (more weight) and since inevitably the gun/armor race will continue it will need more armor to face guns comparable to its own (more weight).

It seems that the practical weight limit of an MBT of about 70-80 tons. There is a reason the concept of the heavy tank was supplanted by the MBT. Even if you have an engine that can move it (and enough fuel). You run into the problem that civilian bridges and roads cannot handle them. Not to mention the impossibility of moving something 80+ tons on anything but firm dry ground.

You could argue that a 130mm+ gun could be put on a vehicle, and then reduce the armor and have it rely on superior range and speed for defense. But at that point that is not really a MBT, with the balance or armor, speed and firepower, but a mobile gun system.

Semantics aside you also run into the issue that the vehicle has to carry less ammunition as the caliber go up. It is likely that a MBT with a 130mm cannon could only carry about 20-30 rounds (this is consistent with rate ammo stores have shrunk from the M48 to M60 to M1), limiting battlefield endurance.

I suspect that we have seen the zenith of MBT main gun calibers with the current generation of technology.

I think that in the next big leap in MBT armament will be to move away from kinetic sabot rounds to either a support gun/ATGM system like the M60A2 had (hopefully with better luck than that system) or to something new like a railgun system.

What are your thoughts? Will we see a 130mm+ main gun on a MBT or has the MBTs hit an evolutionary dead end with traditional cannons?

Rate of change has slowed but i would think you're correct.
Next is some other technology and likely a railgun.
All they need is a better way to store electric or some sort of weird generator.

I think railguns are a bit of a question mark. I think we are still a few years out from them as a practical weapon on a warship or static ground defense. On a MBT? I would be surprised if we are even 10 years from a prototype and by then what will the landscape of MBT technology look like? It is hard to say.
Perhaps a gun fired ATGM system is a good interim solution. But active defenses are getting pretty good and these systems would need to be developed to overcome them.

Part of me wonders if in 30 years eventually the gun/armor race will end and fire power will win out and MBTs will be seen as 20th century anachronism like armored knights of the high middle ages.

Robots will be used in the near future (or ground-based drones if you prefer) and I can see electronic jammers being more useful than old fashioned high-velocity shells, so we could well see the end of the MBT.

I go back and forth on whether drones are the future of warfare or not. It is certainly possible. But I wonder that once drones move from the peripheral to the center of combat if they will not be too unreliable due to jamming/electronic warfare.

The other option would be semi-autonomous AI drones (kind of a spooky thought) but that has its own host of issues. I don't think AIs will stack up well against human opponents. Just look at video games. There is no real time game on the market were a AI can hold a candle to a decent human player.

But if drones can be reasonably well shielded from jamming we may see full drone on drone warfare in our lifetime.

By eliminating the kinetic penetrator and going towards something with a HEAT warhead, the active protection system employed by the defender will become paramount. Less armor needed, easier to strategically move the vehicle. All great and makes a heftier "light" force to deal with small hotspots around the world. Good Idea fairy written all over it until you come up against someone with a kinetic energy weapon that your APS can't deflect and it blows holes thru your "light" armored vehicle.

There will be significant development in the visual spectrum where I can see you and you cannot see me. We really are in the age of "If it can be seen, it can be killed". There are already products on the market that can be fired from a weapon and just need to pass over a target to be able to get a kill. For most of todays weapon systems, just as back in WW2, keep fuel from them and they don't go anywhere.

I'm expecting Active Protection Systems to grow to be able to swat APFSDS. They can already swat any ATGM in service.

I think that we might see some tanks armed with 130 or 140mm guns, but I expect that they will have too few rounds to be usable in extended combat.

Going to something like the MGM51 Shillelagh used in the Sheridan and M60A2 Starship is not really an option, either, because of the APS.

I'm expecting lighter tanks in the future, to be more easily transportable and more mobile. Yes, this does mean less armor, but you get around this by shifting to the naval protection model.

You'd have multiple layers of Active Protection Systems: one relatively long-range (equivalent to the SM2-MR); another one shorter ranged (equivalent to Sea Sparrow); a third even shorter ranged (equivalent to RAM missiles); a final hard-kill system equivalent to the Phalanx gun; plus chaff, flares, and decoys.

As an anti-tank weapon, they can actually get smaller. It is all about the ammo used that will kill a tank.

However if attacking fortifications and buildings larger rounds of HEP work well.
I used a lot of it in 152mm guns on Sheridan's and M60a2.

I'm going to be a bit of a hippie and just say that the combination exponential cost increases in weapon systems and the realization that those will make warn economically untenable, will hopefully see the current generation of tanks as the final generation.

Hopefully someday we'll look at an M1 or T-90 and think it made as much sense as a means of problem solving as the rack or the iron maiden.

The Germans experimented with a 140mm gun a while back, but abandoned it. They are supposedly planning on using a 130mm gun on the Leopard 3. They may also be planning on replacing the 120mm gun on the Leopard 2 with the 130mm gun link link

Read somewhere that the Russians are working on 152mm guns and the T-14 was designed to be upgraded to that in the future……….could be smoke and mirrors……

Since we had the 152mm firing Sheridan and M60a2 since the mid 1960s, why should anyone be surprised at their are many in the experimental inventory now?

It is hard to say what way MBT tech should go. There has been no tank on tank battles between forces with roughly equal training and technology parity since… well you could argue WWII, but certainly no sooner that 1973. Tactically you could argue that tank use is today is very much like in the 1930s. There are a lot of ideas out there but know one really knows what a modern tank battle would look like anymore.

There has been no tank on tank battles between forces with roughly equal training and technology parity since… well you could argue WWII, but certainly no sooner that 1973.

Disagree on how far back one needs to look, but agree on the general premise.

One need look no further back than the mid-1980s for the Iran/Iraq war, to find examples of combat between forces with roughly equal training and technology parity. Credible first-hand sources are a bit limited from the Iranian side, but Iraqi sources are now reasonably available.

However, while the two sides were reasonably balanced on training and tech, they were not first tier in either case, and anyways it was 30 years ago, and A LOT has changed in the technology of warfare since then.

So I do go along with the premise that we are looking at a modern equivalent of the 1930s. There are a lot of ideas, but very little practical experience at the level of combat that these systems are designed for.

I think if we want to reach a conclusion about 125mm guns, we need to break the question down to some component pieces.

1) Do we believe we have reached the end of the kinetic energy penetrator? I do not.

2) Do we believe we can get more velocity out of the same size of kinetic energy penetrators? I believe we are at the point of diminishing returns on velocity. Within the atmosphere, we just can't go much faster without a VERY significant increase in propulsive force.

3) Do we believe we can get more penetration through changes in the construction of penetrators? I believe there is still a bit of room left here for improvements. But we are approaching an asymptotic limit, and soon will enter the realm of diminishing returns here as well. Maybe another 10 or 15 years of progress (just a WAG on the timeline).

4) Do we believe an alternative propulsive mechanism with substantially greater force (to overcome the velocity limits) is around the corner? Railguns have potential. Will they be small enough and mobile enough in the near future? Not at all a sure thing, but worthy of investigation and experimentation. But … see below.

5) Do we believe that automotive propulsion systems will improve in ways that allow even MORE armor to be carried? Or do we believe that active defense technologies will be developed that can degrade the performance of kinetic energy penetrators? I believe some combination of both of these are likely. And that means that it will be possible to build MBTs that have some substantial level of immunity to existing 120/125mm KE penetrators. Then what?

If we believe that kinetic energy penetrators will be needed, and we believe that defenses against them will continue to develop, then we should conclude that KE penetrators need to develop further as well.

If we believe we are at, or near, the practical limits in velocity that can be achieved buring chemical propellants in a barrel, and further advances in the construction of penetrators will provide diminishing returns, then we should conclude we must either move away from burning chemical propellants, or add mass to the projectile. Or … both.

And that will be the key. Because anyone who does only one of the two will be out-matched by those who do both.

Which is why the 60mm APDS-firing guns never took pride-of-place in MBTs. Yeah, you got very impressive performance … for a 60mm gun. But at the same velocities, a 105mm gun did SO much more.

If you solve the problems of rail guns, you get to take away the bulk of chemical propellants. Carry only the projectiles as ammo. Your gun will go up in caliber, probably doubling the mass of the penetrator as a reasonable first step.

Well, you can start to take that step now, if you take something else bulky out of the tank. More compact powerpacks? More compact suspension? Externally-mounted fuel? Reduced crew size? Any of those approaches save space that can be given over to larger cartridges.

As you reach the limits of what you can achieve with velocity and construction of 120/125mm KE penetrators, and consider what happens on the next step of protection for the MBTs of your potential adversaries, the conclusion becomes obvious. You WILL go up to 140mm – 160mm guns. Or you will be at a serious disadvantage in any future conflict. The question is more of when, and how. Not so much if.

At least that's my reading.

-Mark
(aka: Mk 1)

I think we are going to see a tectonic shifted in warfare in the next (and heaven help us when it happens) war between great powers. The more I think about the 1930's analogy the more I think it is wrong. We are not in 1930s we are in 1910s. We have been retreading the tactics and tools of WWII to the point that we can no longer fight the war they were designed to be a part of. What will a war where both sides have cruise missiles, attack helicopters, advanced AA, stealth aircraft, cyber attack abilities and drones look like? We have no idea. Just as in 1914 the great powers of Europe all had experience with machine guns and modern artillery, but they did not know what war would look like both sides used it on a mass scale.

The question is what is our modern equivalent to 1914 cavalry? The tool of war that is deemed indispensable but we have not seen that it is past its' prime yet?

I think if we want to reach a conclusion about 125mm guns, we need to break the question down to some component pieces.

1) Do we believe we have reached the end of the kinetic energy penetrator? I do not.

No, we are not at the end of the KE dart.

2) Do we believe we can get more velocity out of the same size of kinetic energy penetrators? I believe we are at the point of diminishing returns on velocity. Within the atmosphere, we just can't go much faster without a VERY significant increase in propulsive force.

We are getting very close to the upper limit of gunpowder velocity. 1700m/s is about it, I think the upper limit for gunpowder is 6000fps (1828m/s).

So we're probably at the point where we need to change propulsion.

I've seen liquid propellant of various types, but I think the better option is coilguns.

3) Do we believe we can get more penetration through changes in the construction of penetrators? I believe there is still a bit of room left here for improvements. But we are approaching an asymptotic limit, and soon will enter the realm of diminishing returns here as well. Maybe another 10 or 15 years of progress (just a WAG on the timeline).

We're pretty close to the limits, IMO.

4) Do we believe an alternative propulsive mechanism with substantially greater force (to overcome the velocity limits) is around the corner? Railguns have potential. Will they be small enough and mobile enough in the near future? Not at all a sure thing, but worthy of investigation and experimentation. But … see below.

Railguns have been in the works since Marconi's time. The USN railgun is still too heavy for land use, it'd take a pretty impressive breakthrough in materials to get the Navy Railgun down to tank weights.

5) Do we believe that automotive propulsion systems will improve in ways that allow even MORE armor to be carried? Or do we believe that active defense technologies will be developed that can degrade the performance of kinetic energy penetrators? I believe some combination of both of these are likely. And that means that it will be possible to build MBTs that have some substantial level of immunity to existing 120/125mm KE penetrators. Then what?

I don't think that more armor is really an option. The Abrams and Merkava are already considered too heavy. They have limited strategic mobility, or even tactical/operational mobility. Very few bridges can handle a 70-80ton load. Also, heavier tanks require exponentially more horsepower, which means more fuel.

I'm expecting the next generation of tanks to be down about 35-40 tons, with much more capable Active Protection Systems.