In Ukraine, tanks seem to be mostly be used as assault guns. Under those circumstances, I am wondering, do vehicles like the Lynx120 or CV90120 make sense? Or the US 105mm MiniAbrams? Or are you still better off with something like 40mm gun (+ 120mm mortar)?

  When/where/how has it ever been demonstrated that you are better off with a 40mm gun than 105mm or 120mm gun?

we;;, simply put: if the 40mm is powerful enough, then the increased ammo load would make it peferable over the bigger gun

The major advantage a tank has, even old ones like the T-34, is that they're basically immune to man portable kinetic weapons, and all but immune to some HE lobbers too.

Being on the receiving end of a tank's main gun might give you a paper cut.

These two factors combined mean that gun range isn't really a factor, and tanks can roll in to the midst of enemy positions, just like we saw repeatedly during the Ukrainian war.

A (partial) solution for this is to distribute AT weapons down to the platoon level, which is not only expensive but also heavy enough to impair dismount mobility.

Another solution, even more expensive and probably very risky is putting your ATGM armed IFV closer to your dismounts, but this has obvious limitations on mobility (especially within cities) and does basically nothing to deal with airborne threats.

One thing about Ukraine; both sides have been unable to suppress air defense enough for heavy air support, and have had issues sustaining high artillery fire rates. If you had one or both, it would probably be guys with GLs taking out hard points, not tanks. Taking fairly heavy losses while doing it.

That said, AFVs for direct fire are useful. As pointed out elsewhere, they often can survive when used against infantry positions. As much as all of us here like "heavy, HE-oriented" infantry formations, they tend to not be common. And their loadouts as usually proposed aren't really gear towards busting a methodical assault. 40mm GL, Carl Gustav, RPG-X, and various LAAW systems aren't good against tank frontal armor, and most have trouble hitting the tank past a few hundred meters. Stand off 500 meters from the enemy MLR, and blast emplacements as necessary to allow a breakthrough.

It's doubtful that any army will be deploying NLAW/NLAW 2.0 or Javelins in enough numbers to change this scenario. Though, "If you're not carrying an MG, GL, or Comms/drone, you're carrying an NLAW", would be an interesting concept to try in war games.

From what I read, T-55s and Leo-1s are ebing used in those roles, so their armour is not up to snuff compared to modern tanks.

graylion said:

In Ukraine, tanks seem to be mostly be used as assault guns. Under those circumstances, I am wondering, do vehicles like the Lynx120 or CV90120 make sense? Or the US 105mm MiniAbrams? Or are you still better off with something like 40mm gun (+ 120mm mortar)

For a fire support / assault gun, it seems hard to argue with the BMP-3 philosophy of "get both" - a rapid fire 30mm AC + 100mm HE chucker. 

That level of firepower paired with a tanks level of protection would be hell on tracks. 

For a US system, something like the NEMO 120mm mortar, paired with a coaxial 30mm, would be awesome. 

In fact the 100mm shell of the BMP-3 (~13kg shell weight, 250-350m/s velocity) is pretty analogous to the 120mm mortar which averages 13-16kg (unknown velocity.)

Superb article on the BMP-3 I stumbled across:

https://thesovietarmourblog.blogspot.com/2014/10/bmp-3-underappreciated-prodigy.html

That is kinda what I was thinking. MBT armour and mobility, AMOS with 40mn CTA in one turret.

They've made the BMP-3/BMD-4 turret into a sort of drop in modular thing.  How long before we see some of those old T-55s and T-62s with a new, more multi-purpose weapons system?

gatnerd said:

For a fire support / assault gun, it seems hard to argue with the BMP-3 philosophy of "get both" - a rapid fire 30mm AC + 100mm HE chucker. 

That level of firepower paired with a tanks level of protection would be hell on tracks.

I dunno.  What makes you think it would be better than a 105mm gun tank?