US 81mm Mortar Rounds

[Statisoris]

Does anyone know why there are two instances of HE listed for the Off Map, US Infantry Battalion 81mm mortar section? Does the second HE listing represent another type of HE round?

Maybe one of these three?

M43A1 Light HE: 6.87 lb (3.11 kg); range min 200 yd (183 m); range max 3290 yd (3010 m); 80% frag radius 25 yd (23 m) (comparing favorably with 75 mm howitzer); fast detonating fuze (explode on surface).

M45, M45B1 Heavy HE: 10.62 lb (4.82 kg); range max 2558 yd (2064 m); bursting radius comparable with 105 mm howitzer; equipped with delay fuze so some penetration possible for demolition use.

M56 Heavy HE: 15.01 lb (6.81 kg); range max 1300 yards (1200 m); adjustable fuze for quick or delay operation.

Round Type Source: http://en.wikipedia.org/wiki/M1_Mortar

[acrashb]

Educated guess: it is a two-digit field, so there are multiple entries for ammo loads over 99?

[rocketman]

I have wondered the same thing myself, but in that case the first number wasn't 99.

Edit: how appropriate that this was my 99th post!

[akd]

The second HE line is M56 HE Heavy, but as far as I can tell they are never used.

[YankeeDog]

Yeah, assuming they are supposed to be the Heavy HE rounds (and I can't imagine what else they would be), I wonder why BFC bothered to put this ammo differentiation in... AFAICT, there is no way to tell the mortar to use the Heavy HE rounds and I've never seen the AI use them. But maybe there's something I haven't seen or noticed yet in the AI behavior.

IMHO, they should just be left out for off-map 81mm mortars, and we can all make the assumption that the range for the off-map assets is too far for the heavier rounds to be usable (bear in mind that mortars usually try to avoid firing at close to their max range, as the trajectory is flatter and this is usually less desirable, so the practical usage range of the Heavy HE rounds would be somewhat shorter than the max range).

But ideally, for on-map mortars, there should be some way of selecting the heavy rounds, if the range is appropriate. There doesn't seem to be any way to do this in the current UI, though.

[akd]

The HE-Heavy is only available to off-map mortars. Ideally it would automatically used for fire for effect on a bunker or building point target.

[YankeeDog]

One further thought: Perhaps the more important difference in the "Heavy HE" round that the fuse on these rounds can be set for delay, while the regular "light" HE rounds are quick fuse only.

Has anybody checked to see whether the AI will preferentially use the heavy HE rounds (and whether they exhibit any kind of delayed detonation effect), in situations such as point targeting a building or a log bunker? These are the type of targets where a delay fuse would be most useful (and, therefore, most likely to trigger the AI using these rounds, if it will at all). I can't recall having used 81mm mortars against a target like this myself yet.

If no one else knows or gets around to testing this, I'll try to test it when I get home tonight.

edit: ninja'd by akd....

[Pak40]

The US 81mm mortar had two HE rounds. One was much smaller and only had about 1.x lbs of explosive. The other had about 4 lbs of explosive. The smaller rounds I suppose were used for longer range, which isn't really an issue in this Normandy Bocage.

When I get home later tonight I can look up the exact specs on the rounds in a book I have: The American Arsenal.

[YankeeDog]

The US 81mm mortar had two HE rounds. One was much smaller and only had about 1.x lbs of explosive. The other had about 4 lbs of explosive. The smaller rounds I suppose were used for longer range, which isn't really an issue in this Normandy Bocage.

When I get home later tonight I can look up the exact specs on the rounds in a book I have: The American Arsenal.

Three different types of HE rounds, actually. Basic info is in the OP's post. As noted, In addition to the larger HE charge, the other important difference in the heavier rounds is the delay fuse option.

What we do not have which might be useful is typical supply of the various rounds that was available to 81mm batteries in Normandy. The game appears to depict the Light HE round as far and away the most common, with about 1 Heavy HE being available for every 10 Light HE rounds. What is unclear is when, or even if, the AI will actually use the limited heavy HE rounds, since there appears to be no way for the player to specifically order their use.

[gunnergoz]

It seems to me that I do recall being given the option to use the heavy 81mm rounds by off-map mortars in at least one scenario's opening orders. I think they were referred to as "anti-personnel" rounds since the heavy rounds were able to be fuzed for air bursts, whereas the other lighter rounds are set for ground burst only.

[YankeeDog]

It seems to me that I do recall being given the option to use the heavy 81mm rounds by off-map mortars in at least one scenario's opening orders. I think they were referred to as "anti-personnel" rounds since the heavy rounds were able to be fuzed for air bursts, whereas the other lighter rounds are set for ground burst only.

So the heavy rounds are only used for Personnel-type pre-planned barrages to generate airburst? This would explain why I had never seen them used before -- since they have fast response, I usually reserve my 81mms for use later in the scenario.

Not sure this usage restriction is entirely historical, though, since what I've read the timed delay fuse was more intended for busting fortifications like log bunkers, and using against enemy in buildings.

[Pak40]

Gunner, I think it's the opposite. The heavy rounds could have delayed fuzes in order to penetrate ground/roof/or bunkers before exploding. I really don't see timed fuzes working for air bursts very well. You'd have to get it down to a millisecond accurate in order for them to explode the exact moment above the ground.

[YankeeDog]

Gunner, I think it's the opposite. The heavy rounds could have delayed fuzes in order to penetrate ground/roof/or bunkers before exploding. I really don't see timed fuzes working for air bursts very well. You'd have to get it down to a millisecond accurate in order for them to explode the exact moment above the ground.

And yet, this is how airburst was done by all sides in WWII, up until very late 1944 when the U.S. started using radar proximity fuses for the job.

It was indeed tricky, requiring careful plotting and setting of fuses, and it wasn't as precise or accurate as modern proximity-fused airburst. But it was done.

This said, I have never read anything that definitively described timed fuses being used to create airbursts for medium mortars -- the accounts of this that I have read all involved larger, gun artillery. It also occurs to me that it might actually be harder to time the fuse to airburst at the correct height with mortars because of the generally steeper trajectory compared to gun artillery.

[akd]

It seems to me that I do recall being given the option to use the heavy 81mm rounds by off-map mortars in at least one scenario's opening orders. I think they were referred to as "anti-personnel" rounds since the heavy rounds were able to be fuzed for air bursts, whereas the other lighter rounds are set for ground burst only.

"Personnel" mission type is not available to mortars during setup. These were likely 105mm howitzers.

Gunner, I think it's the opposite. The heavy rounds could have delayed fuzes in order to penetrate ground/roof/or bunkers before exploding. I really don't see timed fuzes working for air bursts very well. You'd have to get it down to a millisecond accurate in order for them to explode the exact moment above the ground.

Until the advent of the proximity (VT) fuze very late in the war, this is how air bursts were achieved. In the game, artillery units with time fuzes available can select a "personnel" type mission during setup. This will fire standard HE with time fuzes set to attempt to burst at an optimal height above ground, but you will note that in practice shells burst at mixed heights and some still burst on impact with the ground. "Personnel" is only available during setup due to the extra time and coordination involved in conducting an air burst fire mission.

edit: yes, as YD posted while I was typing this.

As I mentioned above, mortars at the time did not have time fuze ammunition, so this is not an option in the game. M56 HE-Heavy did not have a time fuze but an impact fuze with time delay (all other US mortar ammunition was fuzed to burst instantly on impact, i.e. "super quick"). The purpose was to achieve penetration of cover before bursting.

Again, as far as I can tell, there is no way to cause the 10 HE-Heavy rounds available to be used, but more testing won't hurt.

[Statisoris]

Lots of good info, thanks for all the responses.

[womble]

The fast fuze was actually more likely to cause airburst, as it would be most likely to be set off by hitting overhead cover and still have time to detonate before the shell reached ground zero.

[Pak40]

As I mentioned above, mortars at the time did not have time fuze ammunition, so this is not an option in the game. M56 HE-Heavy did not have a time fuze but an impact fuze with time delay (all other US mortar ammunition was fuzed to burst instantly on impact, i.e. "super quick"). The purpose was to achieve penetration of cover before bursting.

Again, as far as I can tell, there is no way to cause the 10 HE-Heavy rounds available to be used, but more testing won't hurt.

Yea, that's what I figured. It's just too damn tricky to have a time fuze with mortars. There are so many variables when you consider the fact that crews can use a variable number of charges on the mortar rounds. It will certainly effect the flight time of the round.

[YankeeDog]

Ah, here we go. From the horse's mouth, so to speak:

http://www.90thidpg.us/Reference/Manuals/TM%209-1904%20Ammunition%20Inspection%20Guide.pdf

Info on the M56 "Heavy HE" 81mm mortar shell starts on p. 286.

Short version: It's definitely a delay fuse, demolition shell intended to be used against entrenchments, bunkers, buildings and the like. Definitely not capable of airburst.

Now, now we just need to know exactly how to get the mortars to actually shoot them against buildings and bunkers in the game...

[gunnergoz]

I stand corrected - obviously mis-remembered, sorry. I haven't been playing much of late due to other commitments - should have pulled out my references before posting instead of shooting the old mouth off. Especially since I have good references now right on the PC. Oh, well...

[YankeeDog]

OK, ran some informal tests:

U.S. Regular FO, spotting for the 2x81mm off-map mortar battery (which has the 10 HE "mystery rounds" in its ammo count, which we assume to be M56 Heavy HE).

I gave the FO a wood bunker and a building to target. I made sure both targets were relatively close to the FO's friendly map edge, so that range was not an issue (just in case the game takes into account the substantially shorter range of the M56 shell).

Tried various point target orders onto both the bunker and the building. Both pre-planned and regular missions. Mostly Heavy ROF, Quick duration missions from one tube (about 4-6 rounds FFE), since this seemed to me to be the most likely type of mission for a bunker/building-busting mission.

In no circumstance could I get the mortars to fire the mystery HE rounds. detonations of the shells on the building and the bunker also showed no evidence of delay fusing -- all of the shells that actually hit the building failed to penetrate the building at all and detonated on the roof, for example.

It is interesting to note that the targeting pointer does say "strike vehicle" below it when you target the bunker with the FO, so the game "knows" that the bunker is a target distinct from the terrain it sits on. Not sure if the game has any way of "knowing" that an FO is targeting a building, specifically.

Also, regardless of whether you plot pre-planned or regular, there are no options for "mission type" for U.S. 81mm mortars -- you can't do a "Personnel" or "Armor" mission; only "General".

So, I'm stumped... maybe BFC or an authorized beta wants to step in and let us know why there are these 10 special HE rounds in the 81mm mortar ammo readout? As far as I can tell, they serve absolutely no purpose in-game. The only thing I can think of is that perhaps BFC intended to include some sort of feature to allow the use of the M56 Heavy HE demolition rounds, but didn't have time to include the code. So the ammo differentiation is still in the game, but the functionality to use them is not.

Regards,

YD

[Michael Emrys]

The only thing I can think of is that perhaps BFC intended to include some sort of feature to allow the use of the M56 Heavy HE demolition rounds, but didn't have time to include the code. So the ammo differentiation is still in the game, but the functionality to use them is not.

Sounds like as good a guess as we are going to get for now.

Michael

[A Canadian Cat]

OK, ran some informal tests:

Excellent thanks for sharing!

In no circumstance could I get the mortars to fire the mystery HE rounds. detonations of the shells on the building and the bunker also showed no evidence of delay fusing -- all of the shells that actually hit the building failed to penetrate the building at all and detonated on the roof, for example.

<snip>

So, I'm stumped... maybe BFC or an authorized beta wants to step in and let us know why there are these 10 special HE rounds in the 81mm mortar ammo readout? As far as I can tell, they serve absolutely no purpose in-game. The only thing I can think of is that perhaps BFC intended to include some sort of feature to allow the use of the M56 Heavy HE demolition rounds, but didn't have time to include the code. So the ammo differentiation is still in the game, but the functionality to use them is not.

Just so I am clear are you saying the 10 rounds are never fired? So once the mortars are done firing and they say empty there are still 10 rounds left? Some how I have not had 81mm mortars when playing the Americas so I have not seen this.

[YankeeDog]

Excellent thanks for sharing!

Just so I am clear are you saying the 10 rounds are never fired? So once the mortars are done firing and they say empty there are still 10 rounds left? Some how I have not had 81mm mortars when playing the Americas so I have not seen this.

I didn't double-check this in my test, but IIRC the 10 "special" HE rounds behave just like the smoke rounds in that they are also depleted with the final 10 "regular" HE rounds.

So once you've shot off 100 "regular" HE rounds, the artillery asset will show as completely empty of all ammunition, even if you haven't shot off any smoke, or "special" HE rounds (the latter of which there's no way for you to shoot, anyway).