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sburke

Vet Question - Tank infantry cooperation

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Posted (edited)

Reading Echo in Ramadi and in this one combat situation an Abrams section comes up to support some Marines in the middle of a firefight.  The Marines are on the roof of a building with the M1 on the street below.  The M1 is given info on the building they want targeted and prior to it firing the call goes out to the marines on the roof to hunker down and clear the roof.  Due to a bit of mis communication the marines are not aware the M1 practice is to fire 2 rounds.  The marines have started to re-engage when the second round was fired.  The resultant over pressure knocked 2 marines flat and caused them to be evacuated for concussion injuries.

Question is this, in RL what kind of proximity would be expected for units working with armor?  In this particular instance it is a MOUT scenario and the confines of the street channels the pressure wave of the tank gun.  How much impact would that normally have and is there an expectation that infantry should be x meters distant when working with armor?

Edited by sburke

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Tank main guns create noise in excess of 140 decibels. Repeated exposure to this level of noise can cause severe hearing loss and even deafness. In addition, dangerous noise levels may extend more than 600 meters from the tank. Single-layer hearing protection such as earplugs allows Infantrymen to work within 25 meters of the side or rear of the tank without significant hazard. (FM 3-21.20)

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1 hour ago, kinophile said:

I should do a check in game, see where the impact distance is. And maybe see if it varies between MBT types... 

Interesting question, @sburke

I don't think CM simulates this which is partly why I asked.

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Yeah. That diagram is repeated a lot. The sabot petals are the big danger issue. However, I am curious about the actual blast from the muzzle. I couldn’t find any definitive information.

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1 hour ago, c3k said:

Yeah. That diagram is repeated a lot. The sabot petals are the big danger issue. However, I am curious about the actual blast from the muzzle. I couldn’t find any definitive information.

I was more curious about the over pressure. The story was pretty graphic on how it affected those 2 Marines and they were on a roof.  Thinking my troops lying next to a tank as it fires looks kinda dumb. 

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Posted (edited)

I vaguely recall a similar anecdote from (IIRC) Vienna in WWII, a bunch of Soviet troops decided to watch ISU-152s sorting out dug in defenders and took quite a few casualties from flying debris etc. in the process.

1 hour ago, c3k said:

Yeah. That diagram is repeated a lot. The sabot petals are the big danger issue. However, I am curious about the actual blast from the muzzle. I couldn’t find any definitive information.

You can see what a 125mm does here (at 1:39):

That's actually the second time (it also fires at 1:23), but the dumbass filming it is looking straight down the muzzle this time!  :o

Edited by Sgt.Squarehead

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Oh, lol. I'll bet he doesn't do that a second time! I love the crawl afterwards. Who, amongst us, hasn't had to crawl due to something like that? Across time and borders, yeah, brother, I feel it, too.

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Reminds me that in the 1950s there was an Army show called The Big Picture. Every now and then they would have films of tanks firing during training and sometimes maybe even combat. When the cannon would go off the camera which was located maybe 20 meters off to the side would jerk violently, and that was only 90mm. I think you wouldn't want to be anywhere close to the muzzle of even a 75mm.

Michael

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20 hours ago, sburke said:

I was more curious about the over pressure. The story was pretty graphic on how it affected those 2 Marines and they were on a roof.  Thinking my troops lying next to a tank as it fires looks kinda dumb. 

I can only speak from training environments with full caliber ammo for the 84 mm Carl Gustaf.But considering I got blood taste in my mouth and clear pressure change feel all over the body, particularly the torso, when leading the squad and being 5-10m to the side of the damn thing (much less uncomfortable to actually fire it yourself) wearing double hearing protection I can only imagine the "discomfort" of being in close vicinity of a tank 120 mm gun fired in an urban setting. :wacko:

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I have a (very) vague recollection of Pentagon criticism years ago of Abrams as a close infantry support vehicle in Iraq because the 120 high pressure gun's blast placed troops in too much danger. I recall Abrams was described by one TC as 'an over-engineered mg platform' due to the disadvantages of hauling that big gun around with friendly infantry close by. One thing about Stryker MGS as close infantry support. Its primary round is a low pressure 'squash head' round which has less of a charge than even the (discontinued) 105mm smoke round. Firing it is very much easier on the vehicle suspension and on the nearby troops as well.

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I am betting the front line troops would have objected to trying to put the MGS in that role. It wouldn’t survive the combat environment. If on the other hand they were trying to reduce their inventory. . . . :P

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So, I was thinking about this. 

At first, I tried to find blast and overpressure numbers. Yeah: not available.

Next, I looked for safety zones, but a lot of that is populated with range safety (berms, clear zones, etc.). Others are only due to sabot petals. Lastly, hearing damage zones are delineated. Nothing that would work for my purposes.

Finally, I had a realization: the energy spent expelling the round is created by releasing the same amount of chemical energy. This is the same as what an explosion does. The Abrams, firing an M829 round (rough numbers, so don't hold me to A1 through A4), releases about 27 MJ of energy. (KE=1/2*m*v^2)  That should be the starting point to compare the muzzle blast with an explosion.

Some differences:

Muzzle blast is directional. Someone 1m in front of the muzzle would get a much greater effect than someone 1m behind the muzzle. A conical spread would probably model it best.

There is no fragment damage. Sure, rocks, pebbles, etc., will get hurled about, but this is not an explosive held in a case until it overcomes the case's internal tension. The sabot petal danger is negligible in comparison to a bomb/shell casing.

Related to the above, the blast may be mitigated by not being held until the pressure overcomes the shell casing. So, it'd be a "soft" explosion.

 

So, perhaps comparing the muzzle blast to an explosion would work. The propagation front would be a fractal dimension: more than 2D, less than 3D, and directional.

 

What is the equivalent energy release for an RPG7 launch? Or bazooka/panzerfaust? These backblast weapons cause pinning/suppression in game. Well, how much "oomph" do they have in comparison to the M256 cannon on the Abrams?

Anyway, that's how I'd approach this issue to model it.

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Should one also consider the effects of unconsumed propellant (that big 'invisible' fireball).....I'd imagine it's kind of toasty within a certain radius of that muzzle, if only for moment.

 

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46 minutes ago, Sgt.Squarehead said:

Should one also consider the effects of unconsumed propellant (that big 'invisible' fireball).....I'd imagine it's kind of toasty within a certain radius of that muzzle, if only for moment.

 

Based on my experiments with accelerants, campfires, and alcohol, I do not think that momentary flashovers would have much combat effect.  Just sayin'...

;)

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Problem is how would the AI compute avoiding messing with its crunchies...  This reminds me of why gun elevation limits isn't strictly modelled.

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40 minutes ago, Wicky said:

Problem is how would the AI compute avoiding messing with its crunchies...  This reminds me of why gun elevation limits isn't strictly modelled.

Yeah I am not looking for seeing it in game.  Just like we don't have friendly fire for small arms.  The player would have difficulty managing it, the AI forget it.  There are a lot of things that need to be forgone in order for the game to function.  I'd love for tank guns to be unable to rotate in small street confines, but then the AI would be screwed.

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There goes my plan to poke a tank gun muzzle into a building's window, pull the trigger, and then storm in with my troops. 

Brings a whole new level to the idea of a flash-bang.  

;)

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Posted (edited)
2 minutes ago, c3k said:

There goes my plan to poke a tank gun muzzle into a building's window, pull the trigger, and then storm in with my troops. 

Brings a whole new level to the idea of a flash-bang.  

;)

You can achieve the same effect by dropping your knickers with your bum in the window. That “flash” will allow your men to storm the place effectively. :lol:

Edited by Bud Backer
Autocorrect, damn you!

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