20mm or MG against infantry?

[Dr. Rosenrosen]

I'm using PSW222s frequently in my BCR campaign. I notice that these, along with other light tanks (less than 50mm) prefer to engage infantry with just their MGs instead of their 20mm guns. Sometimes between turns, i will order them to use their main guns against these soft targets. A couple questions:

Should I trust the judgment of the AI and let the MGs do the work? Which is more effective against infantry: MGs or these small caliber guns? Does it depend on the terrain that the infantry is in?

If I target something and choose Use Main Gun = Yes, does this use the main gun exclusively, or will they still use the MGs as well?

Thanks,

Dr. Rosenrosen

[Warmaker]

I generally trust the unit's AI and let them use the appropriate weapon on the target. A single 20mm gun isn't going to tear the infantry appart and the MG will function just as nicely.

The only time I interfere with the unit AI's weapon selection is if I specifically want larger calibre guns (75mm or larger) to use HE on a specific point/target. Otherwise, let the TC/Gunner do their work.

[securityguard]

not sure about the mg and 20mm used at same time, but I do know if the AI thinks it shouldn't do something, regardless what you tell it it will do its own thing. I've asked my half tracks to use main gun many times, and they will maybe shoot twice, then give up. This is usually only if they feel its pointless. Its better to area fire, then they wont stop (usually).

[reinald@berlin.com]

This is actually a little weakness of the game engine. 20mm machine-cannons are the single most deadly guns that can be used on infantry.

Why?

Answer: More suppression and shrapnel per time interval than any tank or field direct-fire-gun.

[Ant]

Originally posted by reinald@berlin.com:

This is actually a little weakness of the game engine. 20mm machine-cannons are the single most deadly guns that can be used on infantry.

Why?

Answer: More suppression and shrapnel per time interval than any tank or field direct-fire-gun.

Didn't 20mm come in both HE and AP? I don't know just curious. Maybe if it's AP 20mm then it wouldn't have as much effect on infantry.

[flamingknives]

Didn't 20mm come in both HE and AP? I don't know just curious. Maybe if it's AP 20mm then it wouldn't have as much effect on infantry.

Yes, it did, and all 20mm autocannon in CMBB are equipped with both (usually more HE)

[YankeeDog]

I can't speak to the Real World deadliness of 20mm HE on infantry - I've never seen any definitive real world data on it's effectiveness.

The ROF of autocannons is certainly very nice, but the rather small explosive charge also means low shrapnel velocity, which means poor lethality and area of effect, especially against troops in reasonably good cover.

The overpressure effects of a small shell HE charge are also pretty minimal, so you don't get the kind of stun effects from the overpressure wave that you do with a larger shell.

But I really don't know whether 1 20mm shell is more effective at supressing/killing infantry than 5 7.62mm MG rounds from the coax MG (comparable realistic rates of fire) in the real world.

At any rate, realistic or not, in the game small HE (below 50mm), even from high ROF auto cannons, is not especially effective against infantry. In general, the TacAI is very good at choosing when to use the main gun and when to use the coax MG against an infantry target - it will choose which has the better firepower depending on the target and range.

This is why light tanks often use their coax MG rather than the main gun when engaging enemy infantry at relatively close range. At longer ranges, they will switch to the main gun as the effective firepower of the MG falls off quickly with range, while HE is more or less equally effective no matter what the range (though there is some loss of accuracy at longer ranges, which does effect lethality).

There are times when it is a good idea to manually target an enemy unit in order to force it to use the main gun or not. More often, I find myself manually targeting to tell an AFV to stop using it's main gun and switch to the MG than the other way around. For example, if you're engaging an enemy infantry unit on a crest, much of the HE will fly long or fall short, having little or no effect. In these cases, the MG fire can be more reliably effective even though the TacAI will try to engage with the main gun. Conservation of limited HE ammo is another obvious reason to avoid using the main gun.

As far as I can tell, AFVs cannot use their coax MG and their main gun at the same time in CM, so the only way you're going to get HE and MG fire from an AFV at the same time is if it has a bow or flex-mount MG that it can also bring to bear. This is probably mostly realistic as the two weapons have different ballistics and therefore would require a different gun lay at anything but short range. I suppose it might be possible for a Tank Gunner to fire the coax MG at a close range target while waiting the the main gun to be reloaded, though. I have especially wondered about this in regards to the IS-2 with it's powerful, but low ROF 122mm gun. It would be very nice if the gunner could fire off a couple of bursts of MG fire while waiting the 20-30 seconds it takes for that gun to be reloaded. Again, I don't really know if this is realistic or not, though.

Cheers,

YD

[Dr. Rosenrosen]

YankeeDog, thanks for sharing your expertise and opinions! It's a big help!

Dr. Rosenrosen

[reinald@berlin.com]

The answer is that bursts of 20-37mm (yes, autocannons fire bursts, hence the 'lone round' argument above is wrong) autocannon rounds create a huge amount of "secondary shrapnel", i.e. chunks of wood from trees they penetrate, slices of stone or walls they hit ...

Much more impact and making trees splinter rather than MG bursts. An APC with a machine-cannon is the much more dangerous enemy to infantry in woods than a main battle tank.

[YankeeDog]

Originally posted by reinald@berlin.com:

The answer is that bursts of 20-37mm (yes, autocannons fire bursts, hence the 'lone round' argument above is wrong) autocannon rounds create a huge amount of "secondary shrapnel", i.e. chunks of wood from trees they penetrate, slices of stone or walls they hit ...

Much more impact and making trees splinter rather than MG bursts. An APC with a machine-cannon is the much more dangerous enemy to infantry in woods than a main battle tank.

Yes, I am well aware the HE shells create 'secondary shrapnel'. My point was that for every one 20mm shell that an autocannon fires, an MG24 fires about 5 rounds.

While the 20mm shell does create secondary shrapnel, because it has a small explosive charge, the shrapnel created is generally pretty small and has low velocity. Therefore, it lacks lethality, especially over range.

The question is whether a 20mm shell creates *enough* shrapnel (and throws it far enough with enough velocity) to make up for the fact that a 7.62mm MG has a ROF about five times faster. Keep in mind that the MG not only has a much higher cyclic ROF, but is also belt rather than clip fed, so the operator has to spend considerably less time relaoding it as well. My figure of 5 MG rounds per 1 20mm round is probably generous to the autocannon.

As I said, I don't know the answer, and it probably actually depends on the environment. As you mention, a 20mm shell is going to be more effective at creating secondary projectiles when

hitting things like trees and rocks than a non-explosive 7.62mm round is.

In an open field, though, the 7.62mm MG might be more effective as it puts out more slugs/second, and the 20mm rounds hitting dirt are going to have most of the small amount of shrapnel they create caught by the ground and vegetation.

I am skeptical that a 20mm autocannon would really be more effective when fired into trees than a larger tank gun, though - A larger HE shell (like 88mm) fired into trees creates VERY large numbers of secondary projectiles, and throws them with considerable velocity over a much wider area than a small shell. Furthermore, the overpressure of the explosion itself creates a 'stun zone' that temporarily disables without causing real injury - and effect a small shell just doesn't have to any appreciable effect.

Would 1 88mm shell really be more effective than 10-20 20mm shells fired into the same area,, though? I don't know. Having never been shot at by various types of HE shells while hiding in the trees, I will freely admit that I cannot offer any concrete evidence on this matter. Suffice it to say that I willing to trust that BFC has done their research well, and until someone can offer concrete evidence to the contrary (as in data from real world field tests and the like), I think their opinion on the lethality of MGs vs. autocannons vs. large HE shells is as good as anybody else's.

Cheers,

YD

[Little_Black_Devil]

You guys are missing a crucial point.

Its called a beaten zone.

An auto-cannon, could have one I suppose, but its smaller and less lethal because there is not as much density of fire, despite any shrapnel.

An auto-cannon, uses a larger round, with the intent of either penetrating something, or breaking something apart.

A machine gun on the other hand, is a suppressive weapon. While it can kill people with its bullets - its bullets are of more use to keep an enemy's head down, so that friendly riflemen can get close to assault the enemy's position with grenades, small arms or the bayonet. By their rate of fire, and volume of fire - they put a lot of bullets down range.

A beaten zone - for those who are not aware, is essentially the chunk of land, where all of these bullets land within a given pattern defined by the range the weapon is being eployed at.

I feel I must point out, the machine guns don't fire like rifles do - thats to say, they are not pinpoint accurate. They bounce a bit with the rapidity of the recoil, and they also count on rounds tumbling differently as they fly through the air. This causes dispersion on the ground.

This dispersion, ends up as an oval in shape. Closer beaten zones (to the firing MG), are smaller, and less elongated. Distant beaten zones, are elongated and larger, though with less concentration of rounds.

This is why, its better to use your machine guns at more distant ranges (like 800 - 1800m), so as to maximize the amount of ground they are covering with their beaten zone.

Remember, bullets, though they are going fast - are still arc in flight, particularly at more distant ranges.

All of these bullets - while they do immediately theaten to hit and kill those in a beaten zone, have the effect of cranking up the pucker factor of the same troops caught inside the beaten zone. This means, they are looking for cover or hiding behind cover - to avoid being hit. When they are doing that, they are subsantially less threatening to your own advancing riflemen who will ultimately close with and destroy the enemy.

Its for that reason - that I would rather have a 7.62mm machine gun for anti-infantry work, than an autocannon.

Moreover, you can carry a lot more 7.62mm ammo with the MG, and hide it easier than you can with an auto-cannon.

Auto-cannons have their place, but for engaging Infantry in the open, machine guns would be preferable.

Built up areas, like buildings however, would be a much more desireable target for an autocannon. Concentrations of troops are also meaty targets for cannons.

Hope that helped a little.

[YankeeDog]

Devil -

Your points about beaten zone are well taken.

As you note, comparing HE fire to MG fire is really comparing apples to oranges as they have different effects.

The original question was about "which is more effective" in general, so I was trying to give an idea of why the in-game TacAI, sometimes chooses to use the coax MG rather than a small-caliber main gun. I recognize that inevitably, such a generalized answer is going to oversimplify, though.

In order to really answer the question completely, you have to go into details of not only range, but also terrain, target, desired effect (i.e., supression or elimination), etc.

I didn't mention it before, but the suppression advantage that MGs have is one of the nicely realistic effects of the new CMBB MG modeling. While it's not perfect (for one thing, the beaten zone seems to be kind of one-size-fits-all rather than varying with range and terrain as you describe), the new modeling has some interesting effects on how and when to an AFV coax MG rather than the main gun.

For example, sometimes you want to 'fix' a unit in place in order to capture it or keep it from maneuvering or whatever rather than eliminate it right away. In this case, you're generally better off using the coax MG than the main gun, especially if it's a bigger, slow ROF main gun since a slow ROF means the enemy unit may be able to run away and break LOS before the big gun can get the range and land a killing shot. As you note, though, the beaten zone effects of MG fire will 'knock down' the enemy unit and keep it from moving so that other units can maneuver to encircle it or whatever. This works in CM just as in real life.

I don't think that the CMBB TacAI really takes these issues into account when choosing to use the Coax MG or the main gun, though. It looks to me like the decision is pretty much based on lethality alone. It's hard to see how it could considering that for the TacAI to evaluate the importance of supression vs. elimination, it would have to 'know' what the overall tactical goal was, something which I don't think the current modeling is able to handle. Ultimately, it would be nice if CM incorporated some sort of way to give units SOP orders like "use MG fire on any enemy infantry spotted rather than HE".

Something to think about for the engine rewrite!

Basically, there's always exceptions, and sometimes an MG is better than even a big gun like a 105mm howitzer. It all depends on the situation and what you're trying to do. As the engine gets better, it's my hope that you'll be able to accomplish this more through some sort of standing 'engagement orders' system rather than micromanaging target and movement orders.

Cheers,

YD

[JasonC]

In CMBB, the MG is better for infantry in open ground, and moving infantry in marginal forms of cover (wheat etc). Against trees or better, or against buildings, the MG isn't going to do much at medium range.

The gun is better against vehicles and guns. It is also better against a stationary target in decent cover - like an MG in a wooden building, for example. The 20mm will typically pin rather than break an enemy, in a minute or two of fire. Might or might not get a man or two.

Light armor in general does enemy light vehicles fine, and denies open ground areas to enemy infantry if you have a couple of shooters. Its firepower against infantry is cover is limited - useful additional suppression, but not killing fire.

Full sized tank gun HE will break (and kill) regardless of cover. Only breaking LOS completely is adequate protection, or being unlocated (e.g. too far away for a full ID).