Benefits of larger caliber main guns against tanks

[KV7]

On 6/28/2024 at 2:19 AM, Burncycle360 said:

A small 4th camp that believes future APS will not be able to reliably defeat APFSDS class threats will suggest using novel design approaches / unmanned turrets while also going heavier to class 90 vehicles to defeat the new threats conventionally, but it won't be seriously considered due to weight limitations of supporting assets; you'd not only be replacing the MBT but also all the other supporting assets (LCAC, bridging, prime movers, etc) and will be rejected on cost grounds.  

I can see something like this occurring in a milder form, with something like "part the turret front is resistant to 140mm" type objectives being met with new armour packages and a modest increase in mass and/or smaller profile turret. Or in some Armata style layout, achieving "glacis is resistant to 140mm" level protection, which is possible even with a similar mass to current western MTB. 

Here "140mm" is just a placeholder for whatever similar threat is salient. 

[On the way]

On 6/21/2024 at 4:46 AM, Samsa said:

With the new KNDS and Rheinmetall demonstrators predictably allowing for 130/140mm guns - in my understanding mostly for added armor penetration - I've heard some more doubts about the general usefulness of the larger calibers.

Especally with the rather large amount of documented tank losses recently, I myself also wonder wether that is the right move.

Many of the tanks getting hit and not penetrated seem to be abandoned or at least need to retreat anyways. That suggests, that the tactical objective of "get the enemy out of that area" can be achieved quite often via mission kill without full penetration. 

Plus, even if it weren't so, it seems that engagements vs a heavily armed targets in the frontal arc are a rather small percentage of all tank engagements in this war, making smaller guns good enough for most cases.

Also the most recent designs seem to reduce turret armor and move the crew below the turret ring anyways, making missions kills vs the turret easier for smaller guns. Crewless turrets also obviously rely on sensors for Situational awareness too which, I suppose, are also susceptible to fragment damage from non penetrating hits or HE hits.

I can see the better HE effect of larger rounds as a benefit, but that doesn't seem the driving factor behind these developments to me. Does having the ability to penetrate the crew capsule of an Armata from the front really warrant the costs of increasing caliber?

I know this topic comes up mixed in in different threads every now and then. Still, I'd be interested in hearing some opinions on this in a dedicated discussion

I tend to agree with this. The only case I can see to go to a heavier calibre round in the 130mm-150mm range, would be the greater killing power at a longer range. Assuming the round itself is bigger then say a 120mm/125mm round, you can pack more propellant into it and get it out to a further distance whereby it will still retain decent kinetic end force. With a larger calibre, 5000m kill range might be the norm. 5000m kill range for the current 120mm/125mm is considered an anomaly.  Having said that, how many potential battlefields (other then desert), do you need to kill out to 5000m? And tank engagements using ambush tactics will almost never occur frontally. The opposing force will wait for the enemy column to expose it's side before engaging. Another consideration is the inevitable reduction in belly load when going to a larger calibre. How many tank crews are happy with lesser rounds in their tanks?

[Ssnake]

A reduction in ammo load is not inevitable. The switch to an autoloader and an unmanned turret will free up a lot of volume in a tank. Whether that's used for overall mass reduction, new capabilities, stronger armor, or retaining a similar or higher number of main gun rounds is a decision driven by the tactical demands of the customer.

Whether the current battlefield in Ukrain is an anomaly or the harbinger of a general trend is hard to predict at this point. Both sides have largely neutralized their air power. Cheap FPV drones take over the role of ATGMs, the overall level of air-based reconnaissance has gone way up - but whether that's an inevitability or a result of the lack of low level AAA (and air dominance for either party) remains to be seen. If this is a temporary fluke, duel situations may occur again. Even if they don't and beyond line of sight engagements become the norm, a bigger caliber may still offer benefits WRT terminal guidance packages, sensors, and of course payload.

[Rick]

2 hours ago, Ssnake said:

A reduction in ammo load is not inevitable. The switch to an autoloader and an unmanned turret will free up a lot of volume in a tank. Whether that's used for overall mass reduction, new capabilities, stronger armor, or retaining a similar or higher number of main gun rounds is a decision driven by the tactical demands of the customer.

Whether the current battlefield in Ukrain is an anomaly or the harbinger of a general trend is hard to predict at this point. Both sides have largely neutralized their air power. Cheap FPV drones take over the role of ATGMs, the overall level of air-based reconnaissance has gone way up - but whether that's an inevitability or a result of the lack of low level AAA (and air dominance for either party) remains to be seen. If this is a temporary fluke, duel situations may occur again. Even if they don't and beyond line of sight engagements become the norm, a bigger caliber may still offer benefits WRT terminal guidance packages, sensors, and of course payload.

Have not thought of the "...Cheap FPV drones..." in that way, good point. Will we see cheap drones take the place of close-support mortars or artillery? I am thinking of several such drones carrying the equivalent of a 120-155mm explosive warhead. 

[Ssnake]

I wouldn't rule it out because I try to bridle my fast-judging nature, and to observe more.

But I suspect that we won't see it because while FPV drones might reduce the number of munitions per target, there's currently a limit of volume of fire that they can bring. You'd need autonomous, long-endurance, hard-to-intercept loitering munitions for the task. There are times when you simply want an area effect and then the fire volume of a gun battery is unbeatable. Plus, sensor-fuzed rounds, while being somewhat more expensive than an FPV drone that can carry a 50kg load (for an extended range and duration), are less sensitive to interception so the cost-to-benefit ratio does not seem to tip dramatically in the FPV drone's favor.

Will AI become cheap and localized enough to be reduced into a gun shell-integratable sensor package? Arguably, with higher precision we might be able to afford reducing calibers, and if you can make a 30kg-explosive-shell-equivalent payload fly for 10...100km and loiter over the target area for 10...100 minutes, then autonomously (and reliably) attack discovered targets (and reliably avoid non-targets) with 1...3m precision, it might become a viable alternative. But that's a lot of conditions that depend on unsolved engineering challenges.