Different uses for 155mm and 120mm mortars

[Erwin]

In most NATO missions one has 155mm which is accurate and great for demolishing even large building complexes in urban/buil;dt-up scenarios (the German Campaign "Die Kunst des Krieges" has several).  But, am puzzled about the tactical use for the 120mm mortars.  They don't have the oomph to destroy large buildings and also seem rather inaccurate.  What is the RL tactical use for the 120mm?

[Halmbarte]

120s are thinner walled than 155s because they have less stress in firing, so the 120s have about the same explore amount as 155s. 

120s will absolutely wreck exposed infantry in the open, particularly if you use VT fuses. Buildings will protect from any artillery fire. 

Since the 120mm is frequently the most responsive artillery available I like it. 

H

[Anthony P.]

I'm guessing 120mm mortars are cheaper and more available to infantry units than howitzers are? There's bound to be people with first hand real life knowledge to weigh in on the matter.

I have exactly the same experience of them in game, they're noticeably innaccurate compared to howitzers. Even precision shells are somewhat like putting a modern sniper scope on a blunderbuss: you're not gonna get that much more accurate. Perhaps they're more meant to hit larger targets even with those. I've been using them as I use howitzer precision shells, targeting individual high value assets like MANPADS and ATGMs, but with little success.

[Erwin]

Maybe they are being provided in an ahistoric way in CMSF, but in the German campaign, one is often given several 155mm and only ever one 120mm.  As mentioned, the 155mm is accurate and terrific for destroying large building complexes.  However, it takes just as long to call the 120mm mortars and they are rather inaccurate.  Are starting to think the 120mm is good for area fire over a bunch of roofs to clear them of Syrian ATGM's and RCL's etc.  I used to use 81mm and 60mm for that, but these are never provided (in the German campaign).

I just wondered what the RL use of the 120mm would be.  Perhaps the 120mm can be called in faster than the 155mm in RL?

[domfluff]

As is ever the case, the real-life utility of these is often because they are there.

To take the Soviets, and Soviet-derived forces (so, Syrians and Russians in CMSF and CMBS), the 120mm mortars are a battalion asset, so each battalion would have a battery of mortars embedded within them, and these will always be available to the paper structure of this formation.

122mm and 152mm artillery are brigade-level assets, so will be assigned to the main effort. That's often, but not always, what we're representing in CM scenarios. Call-in times will typically be longer, but not necessarily long enough to matter. 122mm and 152mm howitzers have a significantly longer range than mortars, so there will be tasks they will do which mortars are unsuitable for.

A CM battle is an extremely limited perspective on a wider task. In that specific case, the roles of 152mm howitzers and 120mm mortars are very similar. They are providing the same four basic tasks that artillery carries out, destruction, suppression, obscuration and denial. The HE in a 120mm shell tends to be larger than the 155mm/152mm artillery, so bigger boom for less accuracy. This means that laying smoke for obscuration is the task which mortars are generally strictly better at, but most tasks can be done more or less equally well with either system. There will be some differences in things like the angle of incoming fire. Whether that matters will be terrain dependent.

Accuracy is for the most part unimportant for suppression and denial, and only really matters when you're trying to actively destroy targets, which is a task that 152mm and 155mm artillery will be superior to 120mm mortars at... but still not ideal, since that's a task better suited for rocket artillery and more specialist munitions (sensor-fused munitions, for example), which are often not really a close support artillery role (and hence not necessarily something you'd see a lot of in CM terms).

So, sure, if you want to phrase the question as "Why should I pick this system in a Quick Battle?", the answer may come down to points values, rarity and available ammunition. Mortars tend to be a little cheaper, but that will vary.

If you want to phrase this question as "Why would you put this in a scenario?", the answer is (or should be) that this is something that is available to this unit, in this context.

If you want to phrase the question as "How do I best use this unit?", then there's very little difference in how these are employed, they both do similar tasks to approximately the same degree of effectiveness, with minor differences.

 

[Ultradave]

7 hours ago, domfluff said:

The HE in a 120mm shell tends to be larger than the 155mm/152mm artillery

No. A 155mm howitzer shell has approximately 2 - 3x the warhead charge of a 120mm mortar.  (comparing a US 4.2" mortar HE shell to a US 155mm HE shell). I'm sure other country's ammunition would be in the same ballpark.

Battalion mortars are more versatile, are under the infantry battalion's direct control, so therefore can be more responsive to the infantry. They are also less susceptible to counter - battery fire as they can pick up and move and then re-emplace faster than a howitzer battery. This becomes more important the more modern the era. It is also more of a difference with towed howitzers than with SP howitzers. Even so a 155 battery is a lot of stuff to move and it's all heavy. In the Cold War period to the present, there is usually a 155 (or 105) battery dedicated to each maneuver battalion, and that association is permanent, so that units train together. Obviously that can be modified depending on circumstances, so there is usually a dedicated direct support artillery battery as well as battalion mortars, so response is fast. In WW2 this wasn't the default organization, so call times to the artillery would be a little longer, not even counting the advances in comms since then.

A 155mm howitzer has significantly longer range. While that may be important for targets of opportunity in the rear areas of the enemy, for CM game purposes it doesn't matter much. The normal real life doctrine would be to select firing positions for both mortars and howitzers so that the expected ranges to targets fall at around 2/3 of the max range of the weapon. Mortars then, would be placed closer to the front lines.  In game purposes, if you have off map assets, then they are already placed appropriately and can reach the whole map. If you were playing a game a scale level higher, where you control the batter position, it matters more. 

One last pretty important thing. A mortar section can put A LOT of rounds on the target in a short time. The sustained rate of fire is faster than a 155mm howitzer and they can keep it up longer before having to slow down. A 155 can fire at a high sustained rate but not for very long, if you want to use it again. It just takes longer to load and fire as well.

Dave

Edited March 3 by Ultradave

[Halmbarte]

1 hour ago, Ultradave said:

No. A 155mm howitzer shell has approximately 2 - 3x the warhead charge of a 120mm mortar.  (comparing a US 4.2" mortar HE shell to a US 155mm HE shell). I'm sure other country's ammunition would be in the same ballpark.

Battalion mortars are more versatile, are under the infantry battalion's direct control, so therefore can be more responsive to the infantry. They are also less susceptible to counter - battery fire as they can pick up and move and then re-emplace move faster than a howitzer battery. This becomes more important the more modern the era. It is also more of a difference with towed howitzers than with SP howitzers. Even so a 155 battery is a lot of stuff to move and it's all heavy. In the Cold War period to the present, there is usually a 155 (or 105) batter dedicated to each maneuver battalion, and that association is permanent, so that units train together. Obviously that can be modified depending on circumstances, so there is usually a dedicated direct support artillery battery as well as battalion mortars, so response is fast. In WW2 this wasn't the default organization, so call times to the artillery would be a little longer, not even counting the advances in comms since then.

A 155mm howitzer has significantly longer range. While that may be important for targets of opportunity in the rear areas of the enemy, for CM game purposes it doesn't matter much. The normal real life doctrine would be to select firing positions for both mortars and howitzers so that the expected ranges to targets fall at around 2/3 of the max range of the weapon. Mortars then, would be placed closer.  In game purposes, if you have off map assets, then they are already placed appropriately and can reach the whole map. If you were playing a game a scale level higher, where you control the batter position, it matters more. 

One last pretty important thing. A mortar section can put A LOT of rounds on the target in a short time. The sustained rate of fire is faster than a 155mm howitzer and they can keep it up longer before having to slow down. A 155 can fire at a high sustained rate but not for very long, if you want to use it again. It just takes longer to load and fire as well.

Dave

The TM referenced here https://www.militarynewbie.com/wp-content/uploads/2013/11/TM-43-0001-28-Army-Ammunition-Data-Sheets.pdf says 

M107 = 15.4lbs of comp B vs 

M934 6.59lbs of comp B 

for a ratio of explosive about 2.8x in favor of the 155mm. Which isn't how I thought this worked. 

 

H

Edited March 3 by Halmbarte

[Erwin]

4 hours ago, domfluff said:

The HE in a 120mm shell tends to be larger than the 155mm/152mm artillery, so bigger boom for less accuracy.

I am talking about the game. 

In the CMSF game, the 155mm has a much larger destructive effect than the 120mm mortars. 

The call time for the 120mm is exactly the same as for the 155mm, when using an FO.  When using a regular unit, it takes significantly longer to call to the 120mm.  

It all seems counter-intuitive to me.   That's why I wondered if thie above reflects RL or is an inaccuracy of the game.

[domfluff]

Yes, I was mistaken. The 120mm has more HE per weight of shell, so you can pack more boom into the same 1.5 ton pallet.

[Ultradave]

3 hours ago, Erwin said:

I am talking about the game. 

In the CMSF game, the 155mm has a much larger destructive effect than the 120mm mortars. 

The call time for the 120mm is exactly the same as for the 155mm, when using an FO.  When using a regular unit, it takes significantly longer to call to the 120mm.  

It all seems counter-intuitive to me.   That's why I wondered if thie above reflects RL or is an inaccuracy of the game.

The question you asked was real life tactical use of the 120mm mortar. So I provided some real life background.

 

[Erwin]

Right... so what you are saying is that one cannot use the 120mm in the game as one could in RL as it doesn't have the same destructive properties you are saying it has in RL. 

In CMSF the 120mm definitely has much less destructive power than the 155mm (as well as much less accuracy).  In addition it is slower to call in than the 155mm unless one has an FO.  In CMSF almost any unit can call in the 155mm with about the same time as an FO.  CMSF really needs some major updates.

[BarendJanNL]

From personal experience, 120mm (rifled) at 6km is a lot more accurate when compared to 155mm L52 at 12km, which is apparently not how it is in the games.

[Ultradave]

8 hours ago, Erwin said:

In CMSF almost any unit can call in the 155mm with about the same time as an FO. 

This probably isn't really accurate either. FOs or FISTs are well trained to do so, and have the radio nets "dialed in" and ready to go. The "almost any unit," whoever they may be, will have varying levels of ability to effectively call for fire. Variables like map reading ability, knowledge of the TRPs in the fire support plan (they may or may not depending on the level of command), being able to quickly switch to and make contact with the battery by radio, and their proficiency at using a call for fire, which has a specific format, and how good they might be in zeroing in on target with adjusting rounds, all play a part. It takes some practice to learn how to bracket and estimate distances well. Every battery and mortar section does some training on how to coach an untrained observer, but that adds time to getting the mission going, so mission times for FOs are justifiably shorter than infantry HQ units or whoever else might be calling. 

So, yeah, the general answer is that artillery call and adjusting in CM is quite abstract and generalized across periods, and some things don't carry directly from real life experience. This was my job for years, so I have a lot of detail in my head. Do I need it in the game? Well, I probably would have fun with it as an artillery simulator. Others might find it tedious  

In RL, a 120mm shell does in fact have a lot less explosive power than a 155 shell. I was in the Airborne and our direct support artillery was 105mm howitzers, rather than 155mm. In that setup, a 120 and a 105 are roughly equivalent. Roughly. A 105 also has a lot less explosive power than a 155. 

Hope that helps. Doesn't change anything of course. And my experience is Cold War era, which pretty well translates to WW2 with better comms. There were the beginnings of computerized fire calculations and GPS, but we didn't have those. TACFIRE was a computer based battery fire control system, but it came in 5ton trucks. Can't airdrop those. We had a digital-analog computer that used paper punch tape input (yeah, a dinosaur). It hardly ever worked right and it weighed 400 lbs, and usually broke if you airdropped it. "Charts and darts" (manual paper, protractors and slide rule calculations) were faster anyway. And those methods have changed little since WW2. The physics of ballistics are a constant  

Dave

[holoween]

One thing that isnt modeled at all is safety distance. With a morthar you can fire far closer to friendly infantry before getting danger close. So IRL the last prep fires on a position before infantry assaults would usually be morthars.

[Erwin]

2 hours ago, Ultradave said:

In RL, a 120mm shell does in fact have a lot less explosive power than a 155 shell.

The game does simulate that.  But am curious.  If the 120mm has more HE why has it less explosive power?

1 hour ago, holoween said:

With a morthar you can fire far closer to friendly infantry before getting danger close.

That makes sense.  Unfortunately, in the CMSF game I have found the 120mm to be very inaccurate (and ineffective in destroying buildings).  A POINT target will result in shells landing all around an approx 50m+ diameter.  In the game, the 155mm however, are very accurate (other than maybe the spotting rounds).  

My original question was how do players use their 120mm mortars in built-up maps given these game results?

[Ultradave]

23 minutes ago, Erwin said:

The game does simulate that.  But am curious.  If the 120mm has more HE why has it less explosive power?

Easy answer. It doesn't have more HE.    Scroll back a bit. A 155mm howitzer shell has over twice the explosive weight as a 120mm mortar round.

In general terms a mortar is going to be less accurate than a howitzer. The velocity of the shell is lower, the trajectory much higher, making it susceptible to winds aloft more so than an artillery shell. That's something that can be calculated for and input corrections, IF you have time for it. The artillery battalion Target Acquisition Battery will fly a weather balloon a couple times a day and report direction and speed at various altitudes. You (the various fire direction centers) use those to look up deflection and elevation corrections to add/subract to the firing data, based on your expected direction of fire. Now obviously 2x/day still only gives a rough idea and weather and wind can change, so even those corrections are ballpark. 

In the game, I use mortars for a few things. 1) Against unprotected infantry they are good, or in trenches you'll get the odd direct trench hit which is great, and even if you don't it usually keeps their heads down. 2) Short harassing mission against armor to make them button up. 3) Smaller mortars especially are great for suppressing MG or AT gun positions and are usually quick response.  Against buildings or anything substantial, I leave that for the field artillery, unless mortars is all I've got.  Mortars can do pretty well against pillbox positions too. They probably won't knock them out, but they can suppress them. Nothing like a couple dozen mortar rounds landing on the roof and all around to disorient them and give them a headache. It helps anyway.

Dave

[Chibot Mk IX]

120mm mortar can kill T-34/85 or a Panther with a direct hit.

 in CMSF and CMCW it can be used to destroy the ATGM vehicles.

 

Talking from my CMSF2 USMC campaign experience, 81mm mortar can destroy the pillbox with a direct hit. 

 

[Erwin]

Thanks guys...  What I conclude is that it probably isn't that useful to provide the player with one offmap 120mm mortar unit when the scenario is built-up/urban.  2+ 81mm would be better for KOing ATGM's on roofs and generally keeping heads down.

[Chibot Mk IX]

Because 120mm Mortar is an organic asset in PzG Battalion, while 81mm mortar is not. 

[Erwin]

Mystery solved.  Thank you...