The difference between a MBT and an assault gun

I've come up with a potentially useful definition:

It's an assault gun if what matters most for the commander is the ability to bring to bear heavy weaponry with protected mobility. It's a main battle tank if what matters most for the commander is the ability to keep advancing in face of much resistance.

An assault gun benefits the infantry with many 75-152 mm shells and with a supply of machinegun ammunition that can be brought to bear irrespective of small arms' suppressive fires.
An MBT meanwhile enables mobile warfare at high speeds where lesser-protected vehicles and infantry would be forced behind cover and concealment by opposing forces.

The widespread definition of an assault gun as a turretless AFV with a normal calibre casemate gun is correct from a military vehicle history point of view, but it doesn't help to understand the tactical domain. M4 Sherman tanks employed in tank-infantry teams (with four Shermans supporting a single platoon of infantry in clearing buildings, advancing on trenches and so on) should be understood to have been assault guns in the tactical sense.

M4 Sherman in tank-infantry team
This has far-reaching consequences, and makes it much easier to understand why some land forces use tanks for bold and rapid manoeuvre while others seem unable to do so, despite a large inventory of tanks. Some armies are preferring the assault gun / infantry tank approach, not the more demanding mobile mechanised warfare approach.

Germans did it too, especially Dec 1941 onwards.
Panzer IV in close to camera, assault gun StuG III in background.
This in turn changes greatly how their opponents need to prepare for defence. Assault guns / infantry tanks can be defeated easily with man-portable weapons and munitions by the infantry if they are available in the necessary quantity and quality. Emplaced mines do matter, and even somewhat sluggish artillery may be helpful.

Matilda Mk 2 tank - the archetypical infantry tank,
but only a special CS version had effective HE shells
Meanwhile, mobile mechanised warfare requires either constant attrition by skirmishing or counterconcentrations of anti-tank firepower. None other than highly responsive artillery will be of much help. A reconnaissance and surveillance effort has to inform the defenders. Mobile reserves are required. The mobile tank force would severe its connection with supporting assets, which will weaken it. Its air defences may be overcome by a focused SEAD effort, for example. It will no longer be able to expend as much artillery munitions as it was able to when its supply line was secure and it was able to call on friendly formations nearby.
At the same time, the defenders will be pushed into disorder, forced to evacuate some locations, and their defence must succeed embedded in this disorder.

Once again, the best deterrence and defence bang for the buck would be achieved if the training of the land forces is so good (because of doctrine, training areas, training times, operating budget, personnel system) AND visible (foreign observers of exercises) that both modes are mastered AND potential aggressors are aware of it.
The more highly potential aggressors think of your forces, the less you need of them. Up to a point, this also lowers the costs.*



*: More about this later.


  1. What would a purpose built modern assault gun look in your opinion? Does it have to differ substantially from the MBT? I've been thinking about MTLB with improved frontal armor and CMI 90/105mm turret. Cheap and MOTS.

  2. From this perspective, is it worth designing and manufacturing dedicated assault guns, or should a military use its budget to just buy more MBTs that can be used as assault guns? That way spare parts and maintenance would be shared and there would be some economy of scale.


  3. I think MBTs do just fine in direct infantry support, they have the firepower and protection.

    Yet countries whose army doesn't get mobile mechanised warfare right anyway could stick with cheaper tanks that are good enough for the infantry tank/assault gun role. You can really do with 90 mm for fire support, at most 105 mm. You do not need APFSDS-proof glacis and turret front, and no sophisticated commander's independent thermal viewer. A simple dozer blade is more useful than a high end CITV for infantry support.

  4. This pretty much fits my take on MBT and assault guns and the definition is useful although I would add rapidly or quickly in front of advancing to underline the difference in speed.

    Depending on the circumstances even a very light 4x4 as the famous Panhard AML could both be used as an assault gun or battle 'car'. Indeed similar design still are fighting mostly in the former role as we speak, see the first link below...

    Perhaps it is useful to add the other tactical dimension as armoured reconnaissance vehicle. So we have that role and mentality also sorted out.


    1. (http://www.analisidifesa.it/2016/09/libia-haftar-riconquista-con-un-blitz-i-terminal-petroliferi/)

    1. There's a post in the pipeline that covers this (partially).

  5. The effect on the enemy of the specific preference of tank use is rightly pointed out and perhaps the most important take-away.

    Considering dedicated assault guns I think it's important to point out that with technological developments, tactical trends, infrastructure restraints and army sizes the various trade-offs also shift. Engines, transmissions and suspension for example are less of a constraining factor then a hundred years ago making the trade-off between armor and mobility smaller. Smaller AFV fleets also should force less specialized vehicles of which only a couple might have to be integrated and supported.