75mm Arty Too Expensive?

[Col Deadmarsh]

Why is the 75mm American arty 88pts when it only has 80 shells? The American 81mm arty has 200 shells and is only 11 pts more. What gives?

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Youth is wasted on the young.

[Kurtz]

The 75 mm has higher blast than teh 81 mm.

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SS-Weihnachtsgrenadiere

[John Kettler]

Kurtz,

While I believe that what you're saying is correct in game terms, I confess myself baffled as to how this could be so in reality.

Mortar shells don't undergo the 100,000 G acceleration that field artillery shells do, hence can cram more explosive (blast) into a given bore size than field artillery can, because the projectile walls can be made thinner yet not collapse when fired. It therefore seems odd to me that a bigger bore mortar, firing a less stressed projectile, should have a lower blast rating than a smaller and lighter field artillery shell.

Seems to me it's time for the ammo grogs. Someone's "got some 'splainin' to do." Oh, Bullethead!

Yours in perplexity,

John Kettler

[Shadow 1st Hussars]

A question not worth starting a new thread for: Why does it take 81mm spotters less time to call in the arty than their larger caliber brothers?

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shadow@jagdtiger.de

Canada For CM

I AM CANADIAN!

Eh?

[This message has been edited by Shadow 1st Hussars (edited 03-03-2001).]

[argie]

Originally posted by John Kettler:

Kurtz,

While I believe that what you're saying is correct in game terms, I confess myself baffled as to how this could be so in reality.

Mortar shells don't undergo the 100,000 G acceleration that field artillery shells do, hence can cram more explosive (blast) into a given bore size than field artillery can, because the projectile walls can be made thinner yet not collapse when fired. It therefore seems odd to me that a bigger bore mortar, firing a less stressed projectile, should have a lower blast rating than a smaller and lighter field artillery shell.

Seems to me it's time for the ammo grogs. Someone's "got some 'splainin' to do." Oh, Bullethead!

Yours in perplexity,

John Kettler

The 81mm mortar shell weights around 3 to 3.5 kgs and the 75mm gun shell around 6 kgs... That makes the blast difference.

The 3" British mortar shell weights around 4.5 kgs, and the blast is higher than the 81mm mortar shells.

Ariel

[argie]

Double post

[This message has been edited by argie (edited 03-03-2001).]

[Doug Beman]

Shadow, I think it's because mortar batteries are generally closer to the front lines, and are more flexible in their re-targeting.

But I don't really KNOW, so we should wait for someone with hard knowledge to confirm.

DjB

[Kurtz]

Blast values in the game:

US 81 mm: 18

UK 3" (76mm): 26

German 81 mm: 19

US 75 mm: 39

The 3" mortar has shorter maximum but longer minimum range compared to the US 81 mm

3": 115-2560m

US 81 mm: 100-3000 m

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SS-Weihnachtsgrenadiere

[North Star]

The cost per blast effectiveness of these two weapons is about the same, but the response time is much better on the 81 mm mortar. Because of that, I never take the 75 mm and love the flexibility and quick support allowed by the mortar.

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"Act after having made assessments. The one who first knows the measures of far and near wins - this the rule of armed struggle." Sun Tzu - The Art of War

[Col Deadmarsh]

Uh, wait a minute. So the 81mm arty is off-field but the 75mm is what, an on field mortar and not arty at all? If so, why is it in the arty column and not under support? I'm cornfuzed...

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Youth is wasted on the young.

[Kurtz]

81 mm and 3" mortars are available on- or off-board. 75 mm arty is only available as off-board artillery.

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SS-Weihnachtsgrenadiere

[Guest barrold713]

I would presume that the cost is not solely a product of the effectiveness but a combination of the men, materials, logistics, and availability of the unit in question. If this is true, I suppose that a mortar is cheaper to manufacture, requires fewer men to operate, and does not have the same need for an extensive artillery train (abstractly modeled in CM). If in fact these costs are considered in the purchase points, it would be reasonable for the 75mm to be more expensive.

I could be wrong and I would invite anyone to enlighten me if I am but this makes sense to me.

BDH

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"Democracy is two wolves and a lamb discussing what to have for lunch. Liberty is a well-armed lamb contesting the vote"

- Ben Franklin

[jasoncawley@ameritech.net]

Others have already pointed out the difference in blast. Numerically, the 75mm and 81mm U.S. and German modules are like this (costs are as regulars) -

U.S. 81mm - 19 x 200 rnds = 3800 blast, cost 99 points, blast per point = 38.4

U.S. 75mm - 37 x 80 rnds = 2960 blast, cost 88 points, blast per point = 33.6

German 81mm - 19 x 150 rounds = 2850 blast, cost 71 points, blast per point = 40.1

German 75mm - 37 x 50 rounds = 1850 blast, cost 47 pts, blast per point = 39.4

The U.S. 75mm module is probably slightly overpriced, and a cost of 75 might be more accurate. Alternately, if the higher blast per round is considered more valuable, then the German 75mm is underpriced, and should cost more like 55 points.

I think the first of those is more nearly correct, since I consider the faster response time and suppressive effects of "lots o' littles", with the 81s, fully worth the smaller blast value per shell. Few buy the 75mm U.S. module today, but if it were 75 points I'd certainly consider it more often.

Incidentally, for those interested in realism, the 75mm support module would be the most common type of support for U.S. cavalry formations, and equally common with 81mm mortars for the airborne. In the former case, it is the MGC SP howitzers firing indirect. In the latter case, it is the U.S. 75mm pack howitzer, which was light enough to be landed by glider.

The Germans get 75mm support from the infantry howitzers, which also appear on-map, and from smaller numbers of longer-ranged 75mm and 76.2mm arty (the latter a widely used, captured Russian weapon). This would be quite common in infantry formations, less so in Panzer or SS ones. Those usually had 75mm infantry howitzers too, but mounted on halftracks and used by the Pz Gdrs as assault guns (the SPW-251/9), for direct fire.

Incidentally, I recommend the German 75mm module highly, on defense. Its punch is intermediary between the 81mm and the 120mm or 105mm, about twice the former and half of the latter. It is a very cheap module, ideal for a flank held by a limited force (like 1 platoon, small teams, and minefields).

[Vanir]

Originally posted by jasoncawley@ameritech.net:

The U.S. 75mm module is probably slightly overpriced, and a cost of 75 might be more accurate.

It's definitely overpriced. Consider that its response time is twice that of the US 81mm mortar (2 minutes vs. 1 minute). No wonder nobody ever buys them.

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What a bunch of horsecrap. -Steve

[KiwiJoe]

You don't mention 1 of the most important factors to consider when buying artillery: time to fire for effect. A (reg) German 75mm takes 4 mins to call in. This is simply far too long to be of any real use. You almost have to be a mind reader to drop your rounds on the enemy. Mortars take less time to call in than field artillery and thus are far more effective.

[jasoncawley@ameritech.net]

Well, I generally don't have too many problems with the delays, but maybe that is from being an artillerist - or I suppose it could be playing the Americans, or the Germans on defense when I do play them. On defense as the Germans, I use a TRP. Works fine for me. And once a barrage is down, you can "walk" it.

[Guest Andrew Hedges]

In evaluating how many points different artillery is worth, it's important to keep in mind that the artillery's effectiveness also depends on the type of battle you're fighting. In a meeting engagement, the 81mm mortar is great -- it has a lot of ammunition, it has enough power to suppress or break up an attacking force, and it arrives quickly enough to call down on an enemy force you just discovered.

In an attack, assault, or as the attacker in a probe, 81mm mortars are much less useful because they simply don't have the power to blast infantry out of foxholes or heavy buildings. The quick response time is less critical in an attack situation because it's unlikely that there will be an enemy attack you'll need to break up, and you can easily wait longer before dropping the arty on the entrenched enemy. The ability of the 81mm mortar to drop smoke is still handy, though. But for an attack, you really need something that can blast the enemy out of their foxholes.

81mm mortars have some advantages on the defense -- as in MEs, they will break up/suppress attackers, and they will come down quickly. However, as a defender you have TRPs available, so almost anything will come down quickly. Also, the 81mm mortars won't do a lot of killing for you, unless your attackers stay in trees. When mortars are effective in MEs, it's usually a combination of the mortars breaking up the attack combined with infantry shooting up the suppressed units. This can happen in an attack-type scenario, too, of course, but sometimes it's better for the artillery to do the suppressing and the killing, either because you don't want to expose your infantry, or because you are very outnumbered, or both.

[John Kettler]

argie,

Oops! Tripped on my own argument.

Let me regroup. Clearly, I was partially braindead when I made the post. I should've said "smaller and heavier" projectile. Forgot my own wall thickness point!

My original objection remains, though. If the lethal mechanism for these projectiles is in fact blast, presumably derived from the amount and type of explosive fill, then given even rudimentary knowledge of artillery shell fill fraction vs. that of mortar shells, it still seems obvious to me that the mortar shell should clearly have the blast advantage in such a comparison. This doesn't even take into consideration the better fragmentation pattern caused by the mortar shell's steep trajectory.

Where are Bullethead, Jeff Duquette and rexford when you need them? Speaking of Jeff, did you get my E-mail?

Still perplexed,

John Kettler

[John Kettler]

Still waiting to hear from the ammo grogs on this matter!

Regards,

John Kettler

[Guest aaronb]

Originally posted by John Kettler:

Still waiting to hear from the ammo grogs on this matter!

Regards,

John Kettler

Not an ammo grog, but:

- the 75mm cannon round has a large powder charge, and can then achieve decent range with a heavy (bigger blast value) projectile.

- the powder charge on the 81 is much smaller ,because: it sits on the ground, not a carriage with recoil buffers, and the total weight (gun+ammo) is intended to be man-portable. So the projectile weight has to be lower for a decent range.

How's that sound?

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my armoured assets have about the half-life of a gnat in DDT

- Germanboy

[John Kettler]

aaronb,

Thanks for responding! I understand what you're saying, but the issue isn't how far the projectile can be thrown. The issue is how much explosive and of what type is in the two projectiles.

Typically FA shells have relatively small fill fractions. Mortar shells, being far less stressed by acceleration forces, much like rockets, have significantly larger fill fractions. I'm looking for some hard numbers on both projectile weight and explosive fill straight out of ordnance official data. I simply don't see how what some are asserting can be true.

Regards,

John Kettler

[Kanonier Reichmann]

Originally posted by John Kettler:

aaronb,

Thanks for responding! I understand what you're saying, but the issue isn't how far the projectile can be thrown. The issue is how much explosive and of what type is in the two projectiles.

Typically FA shells have relatively small fill fractions. Mortar shells, being far less stressed by acceleration forces, much like rockets, have significantly larger fill fractions. I'm looking for some hard numbers on both projectile weight and explosive fill straight out of ordnance official data. I simply don't see how what some are asserting can be true.

Regards,

John Kettler

I'm no artillery grog John but have you considered that if the shell casing on an artillery shell is much thicker than a mortar shell then it's likely to fling out much more shrapnel upon explosion, hence a higher blast rating in CM to model the greater and heavier number of fragments. Well it makes sense to me anyway...

Regards

Jim R.

[John Kettler]

Kanonier Reichmann,

Your post sent me to the CM manual, page 64, where it says:

"The firepower of these weapons is represented by a BLAST VALUE, which is a rough measure of both the size of the shell and the amount of explosive charge it carries."

If we take the manual as written, then your argument about massy fragments isn't addressing the fundamental mechanism allegedly being modeled in the game, which is blast.

You and I know that blast and fragmentation (not shrapnel, gah!) effects both figure into a true lethality calculation, which varies depending also on the target hit. A truck can survive a great many fragment or small projectile hits and still function. We learned this the hard way in Vietnam interdicting trucks on the Ho Chi Minh Trail. That's why AC-130s have a 105mm howitzer--one hit=no truck and cargo, rather than just a temporarily disabled truck. Conversely, men can be surprisingly blast resistant, yet are highly vulnerable to shell fragments.

It therefore seems to me that we really need to hear from the ammo grogs. I know I don't have the explosive fill values for even one of the projectiles being discussed here. My references simply aren't up to such a detailed

ordnance matter. How about it guys?

Regards,

John Kettler

[Guest aaronb]

Originally posted by John Kettler:

[...]the issue isn't how far the projectile can be thrown. The issue is how much explosive and of what type is in the two projectiles.

It's the same issue. If you put lots of explosive and casing on a round with a small propellant charge (mortar), then the round doesn't go that far. So you lighten the round to give back some range, sacrificing blast effect for portability (weight of propellant charge and gun system managing said charge).

The final word will come from someone who has a well-considered chart that lists the 'actual' stats for the propellant/bursting charge in the two gun systems.

So, someone, anyone - got a source to quote?

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my armoured assets have about the half-life of a gnat in DDT

- Germanboy

[jasoncawley@ameritech.net]

A few numbers, but I doubt they are definitive. There are too many different kinds of ammo for both general weapon types. Part of this is a reprise of the wide range of 75mm types, debate.

First the basic info. The typical 81mm mortar shell, counting its propellant, is around 7-8 lbs weight /3.5 kg. The most common German one, for which I found data most easily, had a bursting charge of 550 grams. Almost all the German 81mm ammo produced, seems to have been of this variety.

In the U.S. army, there was a shorter ranged, heavier 81mm mortar bomb type made, and called "heavy HE" rather than light HE. But I have no idea how many of them were made, or used. They weighed 11 lbs instead of 7 lbs, and had a limited range, around 2.5km rather than 3.3km for the lighter standard (7-lb) HE.

75mm shells vary considerably, but the most common weight given for German 75mm *HE*, is 13 lbs, 6 kg. So it is a much heavier physical item. But the size of the bursting charge for German 75mm varies. The largest type is listed as 860 grams bursting charge, and that type was *capable* of being fired from, for instance, the L24, L43, and L48 guns on the Pz IV series (where I got the data).

But that doesn't mean that is what they had. Another HE type for the L43 and L48 guns, had only a 454 gram bursting charge. A HEAT round for those types had a 524 gram charge. Other HEAT that could be fired from the L24 or the longer L43 and L48 had charges from 555 to 604 grams. Another fellow has cited the figure of 680 grams for at least one version of HE fired by the longer gun in the Panther, but I can't independently confirm that number.

I am aware that HEAT is a relatively poor HE round. But were they so aware of the fact? That is, did HEAT get issued as a supposedly duel-purpose round? Seems possible. The Germans made 4 million HEAT rounds for high velocity 75mm, along with 5 million AP and 8 million standard HE. Production of HEAT for those guns trailed off in 1944, though, and ceased before 1945.

What I most sincerely doubt, is the notion some seem to entertain as possible, that since a 860 gram HE round apparently existed for a range of German 75mm gun types, that must be what they always fired when firing HE. They made another with a 454 gram charge, and I haven't been able to find out how many of those, compared to the other type. But they certainly made 4 million HEAT, with smaller loads than the peak one, slightly more than the lesser one.

What I suspect, is that the typical German 75mm HE actually had more like equal bursting power to their 81mm mortar bomb. The vanilla-designation Sprgr-34 had 5/6ths as much charge in it. The HEAT rounds had charges very close to it, but with the drawback of HEAT as an fragmentation generator. And we know for a fact they made millions of these rounds.

The HE load figure cited by one fellow for the higher velocity Panther gun, had one ammo type 5/4 as high, and there is this Sprgr-KwK (34) with 3/2 as much. But I have seen no evidence these types were common, nor rare really. No one has given any production or field deliver numbers for any of the types, that I know of.

Incidentally, the production figures for 75mm types I cited about (8m HE, 4m HEAT, 5m AP) do not include 4 million 75mm for mountain howitzers, nor 8 million 75mm for infantry guns, almost all of it HE. They were just for the higher velocity types, but they do include the towed PAK of course.

Naturally, the HE charges for these mountain howitzers and the infantry guns could be quite different again, from the German tank gun figures. And they are the guns that are really being represented as an off map 75mm module.

U.S. 75mm and similar types, also varies. The 76mm had a small bursting charge of 390 grams, while the slower 75mm short had a 690 gram bursting charge. That puts one of them 5/4ths the explosive of the German 81mm, the other 7/10ths. I have not been able to find the gram of HE for the pack howitzer, used in the U.S. airborne. I think that is basically the same gun as that on the M8 HMC. Those two are the likely sources of the 75mm artillery module for the U.S. side.

If one believes that the 680-860 gram range is right for typical HE rounds from lower velocity tank guns, and if one just assumes that the figure for low velocity howitzers and infantry guns will be the same or higher, then it might seem sensible to rate 75mm as considerably higher blast than 81mm. But if the realistic range for most *fielded* ammo is more like ~500 grams, down some for U.S. 76mm, up some for U.S. short 75mm - with anything in the 860 gram range quite rare - then the picture reverses itself, rather.

Other sources I have seen compare the effective radius of the 81mm with the 75mm, and call the comparison favorable. And some even claim for the 11 lb bombs, a favorable comparison with 105mm. I am inclined to doubt the latter in practice, from accounts I have read of the effects of the different weapon types. It may be that the 11 lb "heavy HE" were simply not used much, perhaps because troops disliked the extra load of carrying them, and the idea of being outranged by the enemy replies.

Incidentally, off the subject really but simply because I found it out trying to answer your sensible question (which just a shell type can't do, without production figures for it as well), I noticed some interesting factoids about German shell production by type.

The main morale is that 105mm was by far the most common artillery round fired, with the 81mm mortar a close second. Both of those are in the 100 million produced range (the 105s a bit more, the 81s a bit less). Next comes the 150mm howitzer, with 28 million produced, far more than you might think. For comparison, there are only 8 million 120mm mortar rounds made, and 5 million 150mm rockets, and 4 million rounds for 150mm SiG. And those are the *common* types of heavy artillery, after the "big three". There are barely more than 1 million of all heavier rockets combined, for instance.

Basically, when a German unit called for fire, the company and battalion could support with 81mm. A real artillery battalion assigned to help could support with 105mm. Occasionally division would support with 150mm, or more rarely, some other more ad hoc form of supporting fire would be provided. That being a mix of 120mm, 150mm rockets, 150mm SiG, a grab bag remainder of much less common types.

But another interesting fact is that the scale of the common indirect fire weapons (81mm, 105mm) is noticably higher than that for direct fire types. There you see ~25 million rounds 75mm, 2/3rds of it higher velocity types as opposed to infantry guns, and ~15 million 50mm. (The old Pz III fleet, and more mid-war 50mm PAK than people sometimes imagine).

Anyway, just some numbers to digest. In substance, I do not think your intuition in the matter is off. The 75mm round is a physically much bigger and heavier object, but more of it is metal and less explosive. The size difference *does* balance the metal-to-pop edge of the mortar round, about, but it does not swamp it.

I end with an incidental challenge contest for the ammo grogs. If anyone wants me to believe typical late-war German tank guns, fired HE shells with 860 grams burster, they have to find some *production* numbers for the appropriate round (Sprgr KwK (34)).

Call me a skeptic. The truth is I am not an ammo grog at all, despite what this post might suggest. I am a force-mix grog - LOL. And I have noticed already a definite tendency, to assume that if the best whatsis designed or fielded is X, then the capabilities of X are the standard for all fielded forces. Without attention to the niggling little detail, of whether there was enough X to go 'round.

[This message has been edited by jasoncawley@ameritech.net (edited 03-06-2001).]