Direct hits on theoretically confined units

[Wartgamer]

http://www.battlefront.com/discuss/ultimatebb.php?ubb=get_topic;f=30;t=003726

I think the data in the thread Veritible clearly defeats Jason's theories.

You can't attrite what you can't get at.

Fireplan for VERITABLE

Main Plan:

576 x 25-pr. (221,758 rnds PD, 1,200 rnds VT)

248 x 5.5-in. (53,646 rnds)

32 x 4.5-in. (incl in 5.5-in total)

76 x 3.7-in. HAA guns (20,616 rnds, all airburst)

36 x 155mm (4,688 rnds)

40 x 7.2-in. hows (2,593 rnds PD, 432 rnds VT)

4 x 240mm hows (48 rnds)

2 x 8-in. guns (24 rnds)

12 x rocket projectors, each with 32 rails. (5,730 rnds)

Total: 1,014 guns* (plus rockets), 306,047 rnds (5,433 tons)

Pepperpots:

114 x 40-mm Bofors LAA guns (100,000 rnds HE)

24 x 17-pr A-Tk guns (4,000 rnds)

60 x 75mm (Shermans) (17,000 rnds HE)

80 x 4.2-in mortars (24,000 rnds HE)

188 x MMG (Vickers) (2,000,000 rnds)

Total (excl MMG): 278 guns, 145,000 rnds (520 tons)

Area to be assaulted was bombarded from 0500 till 0920 08FEB45, then from 0920 for six hours a barrage was fired to support the infantry as they advanced. Enemy consisted of German 84th Inf Div, in particular the forward 5 bns. 1,115 PWs were captured from these units, and it is estimated that the fireplan killed or injured a total of 60 men. An unreported number were killed during infantry combat. Total enemy strength in the area was estimated at 2250-2700 men, so about 3% of this combat strength was lost to the fireplan.

Neutralisation was 'complete' however, and comms throughout the div were rooted, which among other things rendered the German arty that did survive - about 2/3 of the 147-odd pieces supporting the 84th Inf Div - useless.

UK/Can inf cas during this phase were 459, incl 110 on mines, spread across 12 bns.

Jon

Edit: revised numbers based on better info. There is confusion in the sources between the amount dumped, the amount fired, and the time frame in which rounds were fired. The above info is from ORS Report No.26 - Fire Support in Operation VERITABLE, Effect on Forward Defensive Positions.

* Guns were from:

24 fd regts

20 mdm regts

3 HAA regts

19 hvy btys

1 super hvy regt

1 rkt bty

[ March 12, 2005, 06:10 PM: Message edited by: Wartgamer ]

[JasonC]

You can't calculate direct hit chances by looking at 100 rounds fired by one gun at one slit trench. They are fired into a wide area, in which there are a lot more slit trenches, not just one.

The proper analysis is to look at a barrage by a battalion or so of guns, not with perfect targeting, on a wide area occupied not by one position but by a whole formation's worth of them. As in, each of 12 guns fires 15 to 25 times, 180 to 300 rounds of 105mm land in the impact area.

The range probable error is amplified by uncertainty of 50-100 yards in their aim points, on top of the error around the point the gun is actually aimed at. The deflection error is amplified by the fact that batteries are shooting in parallel, not converging sheafs on a single point target. The firing guns are up to 50m apart. In addition, there are errors of a half a mil to a mil in their deflection, for each gun, from the battery deflection setting. The batteries are firing to converge on the same area.

The overall result is that the rounds are going to land in a wide oval or circle around 200 yards on a side. The shell density per square yard is higher toward the middle of this region, but not ridiculously so. It is something reasonably close to a gaussian with SD 100m, random angle.

But what is the target area? Is it one slit trench 1m wide, or full trench 2m wide? No. It is all the infantry fighting positions in an area 200m across, which certainly contain a platoon and might contain a whole company. Calculate the surface area of all of their fighting positions, not of one of them.

Now, each shell hits somewhere. Direct hits are occupied surface divided by surface, with (if you want - it will be more exact but you'd be in the ballpark with a flat-weight average) a weighting function or density measure based on the dispersion around the aim point. (That is, the target surface areas in the middle count for more, those near the edges count for less).

Near misses are also going to be common. To calculate those, you extend the surface area around each defending position, and subtract out the direct hit area already accounted for (leaving an annulus). E.g. a foxhole might count as 1m area for direct hits. To ask about near misses within 3m, you have an area of about 27 m.

Back o the enveloper - 7857 m2 middle area, 26302 m2 farther area. Assume a platoon in the former and 2 more plus weapons in the latter. A mix of foxholes and trenches, 1.5 m2 average per man, with 40 men in the middle area in 20 positions and 120 more in the farther area in 60 positions.

Area of direct hits in middle - 60m2. Of direct hits in farther - 180 m2. Of near misses (3m) in middle - 500 m2. Of near misses in farther - 1500 m2. Chance of direct hit per shell in middle - 60 / 7857. Of near miss 180 /7857. This applies to half the shells, and they are not independent. Direct hits in farther, 180/26302, near misses 1500/25302, the other half of the shells, also not independent. 90 to 150 shells in each half, in steps of 10.

Trivial to code. A 100 trials, here are some averages. The format is simply a 180, 200, 220, et shell shoot, up to 300. First direct hits and then near misses -

DHs - 1.22, 1.52, 1.74, 1.47, 1.90, 2.07, 2.31

NMs - 6.04, 6.50, 6.86, 7.75, 8.22, 9.18, 9.94

Shells fired per DH in the range 125-150. Shells fired per NM around 30.

[Wartgamer]

I have someone sending me a copy of a document about German field fortifications.

The basic practice is having weapons pits with soem means of getting to shell-proof cover. So you have troops that can low crawl, rush to arty defeating areas. They don't stand still like some zombie force.

Getting the shell proof dug is a priority before developing the rest of the weapons pits, etc.

[Wartgamer]

You can certainly look at one gun. At DBP, thats probably what was happening. Individual guns were targeting individual targets.

2% 7% 16% 25% 25% 16% 7% 2%

This is about the layout that dispersion takes across a modeled rectangle. Imagine a rectangular field with 8 zones of equal area marked out. Depending on where the infantry 'front-line' is situated, the numbers there are used. So a 50% zone data means the two center sections. If a weapon has a 96 yd 50% zone, then the total length of 'all' shells is actually 384 meters long (?). Very few fall in the outer 2% zones (48m each). The lateral math is similar but its narrower. 10 yd lateral zone translates to 40 yds width.

The infantry line is almost nearly perpendicular to the line of fire. In general, a line of front line positions are layed out so that each position is seperated by roughly equal distance. They are spaced out along the front. They are not spaced out in depth towards the rear. Most front line units adopt this posture. Even mortar platoons are arranged this way. They may have lucrative depth targets, like ammunition behind them, but weapons and people are always parallel to the front lines.

So how good a shoot you have is really which of the zones the gun (s) get across the front line.

In the case of one gun firing at one trench 2ydx4yd modeled vulnerable area (this includes near misses that will be caving in trench sides and injuring occupants), lets say that one of the two 25% zones has been achieved (about as good as it gets). That is, the small trench is physically inside the 25% zone for both length and width.

Roughly, if 100 shells are fired at the target, 25 will land in the 25% box, the total box area of 48ydx5yds=240yds^2. Since the target is only 8yds^2, its only 8/240=0.0333 the area.

Note that I am also using the fact that the trench is located in the 25% lateral area, in other words, its about as good as it gets for the arty. But the rounds in this box has to also reflect that 25% again are laterally 'reduced'. You would have to fire approx 460 rounds or so to get this target.

Note that you would have needed to have centered the dispersion on the target. In other words, directed fire by some means. It would have taken a dozen or so rounds to achieve this. This is overhead and sould be applied also.

It does not matter if you have 4 guns converging fire 120 rounds each or one gun firing 460 times. Technically, if the gun is fired at a slow enough rate that the heat does not effect the trajectory. In reality, if you were firing multiple guns to converge, not every gun gets its 25% zone on the target. They are errors and some guns may be long or short and only getting 10% zones 'applied'. Longs and shorts are generally wastes. They are also a danger to friendlies. Creeping abrrages have a habit of killing friendlies because of this.

The rather narrow width of the dispersion compared to the rather long length means that troops will spread out along the front lines. If they must bunch up, they must have 'shell-proof' cover readily available. Keeping positions 50 yds apart is advisable. One guns dispersion is then not translated into collateral kills. Another improvement is using any fold in the land so you can dig in a protective position that benefits from any 'reverse slope'.

A squad in the field would spread out with individual soldiers having intervals but once shells starting falling, they should all converge to small protected bunkers. Thats what really happens.

[ March 13, 2005, 09:40 AM: Message edited by: Wartgamer ]

[Wartgamer]

The following will serve as a guide for the construction of positions on average terrain:

Available time Type of construction

A few hours

Machine gun and rifle pits, affording protection against machine-gun fire and fragments of shells with impact fuzes. Simple wire obstacles should be constructed. In the case of light machine guns, antitank rifles, heavy machine guns, light mortars, and antitank guns, overhead protection for riflemen and their weapons may be provided at the same time. With heavy mortars, light infantry guns, and heavy infantry guns, overhead cover for the crew must be constructed before that for the weapon.

Half day Thorough construction of pits and recesses under parapets, providing protection against light high-angle fire and splinters from richocheting and time-fuze shells, protection against weather, and increased comfort for the crew

Whole day Strengthening of wire obstacles, strengthening of pits and firing bays. Connection of weapon pits within the system by crawl or communication trenches.

Several days Continuous trenches.

Several weeks Systematic construction of defenses with continuous trenches and shelters.

German Report

[jacobs_ladder2]

Originally posted by JonS:

Also, and the main point behind phased fireplans, as you get closer you need more accurate (read, smaller PEr and PEd) weapons, with smaller areas of effect. This means that you can lay fire more accurately on positions id'd during the advance, and your own infantry can approach closer before the fire has to lift to avoid excessive FF cas. Artillery has a very large PEr. LMGs firing from ~100m have a very small PEr. And, the LMG gunner can see the assaulting infantry. Guess which order they come in the plan?

I know I will regret asking this but here goes...

PEr? PEd? Huh?

[JonS]

Probable Error (range) and Probable Error (dispersion). In other words, the amount of error to be expected from random sources both in terms of range (along the shells intended line of flight) and laterally (left or right of the LOF)

In practice, PEd is negligible when compared to PEr - and neglected when adjusting artillery fire for example. PEr isn't, and is a function of primarily - among other things - overall range from guns-to-target. A various ranges, and for various weapons, PEr is known (in the statistical sense), but once the rounds are falling within it (in other words, within the PEr distance from the intended target) no further adjustment is practical or worthwhile - you're just messing about with random events.

So, from a fireplanning perspective, having the smaller PEr weapons systems firing last means the infantry can approach closer to the enemy while under some form of protection (albeit perhaps not as effective as 7.2-in Hows).

Clear as mud? Hopefully. Please ask if it isn't though.

Jon

P.S. on a pedantic note, the 'r' and the 'd' following the PE are usually written as a subscript, but my UBB-fu is weak today.

[jacobs_ladder2]

Originally posted by JasonC:

Bernard Fall, "The Seige of Dien Bien Phu", p.88 and following -

On December 26th. Col. de Castries issued an order to all units...The big difference between WW I and II in this regard wasn't that tanks won by driving around the other guy (though that did of course happen, especially early against inexperienced enemies etc). It was just that fronts that move at all - even just a few miles a day - never really get arty proof. And as a result, whoever has the logistics bleeds the other guy to death - pretty rapidly, operationally speaking.

More posts like this one please.

I hit this thread with a search and it is answering a lot of questions for me. But one thing I remain unclear on is the role of "light" vs. "medium" mortars.

The 50mm mortar for example seems to have been discredited during WWII. Is this true? If so, why?

How valuable was it to have the support of a 50mm mortar? How much more valuable was a medium weapon such as 81 or 82mm mortar? What did these weapons really accomplish?

Cheers

Paul

[JasonC]

Wargamer still can't wrap his mind around the concept of a larger target, and that firing at 50 infantry fighting positions with 12 guns is much easier than firing at 1 with 1, times 12. The entire error pattern is within a battalion's footprint. The only remaining relevant factor is what portion of the battalion footprint the total area of the fighting positions occupies. See above for actual results of realistic estimates on that score - 1 in 30 hits within 3m, and 1 in 125-150 hits bang on.

[JonS]

Originally posted by jacobs_ladder2:

The 50mm mortar for example seems to have been discredited during WWII. Is this true? If so, why?

Well, AFAIK the US Army still has 60mm mortars down to quite a low level (coy?), and 40mm greanade launchers are all the rage at this years fashion shows, so I don't really know that the idea of light mortars is all that discredited.

As to the advantage of larger calibres ... it comes with costs too. The lower the echelon at which a weapon is held, generally the faster a commander can get support from it. Also, having weapons within his own organisation means that the commander can order support from them, rather than requesting it. Too, lower echelon weapons tend to be smaller and handier, meaning they can keep up with the infantry, and place fewer demands on the Q system in terms of ammo tonnages to be moved.

OTOH, heavier, higher echelon weapons - when they do respond - can intervene with a far heavier and more sustained amount of firepower than can be generated at the pn/coy/bn level using organic weapons only.

[Michael Dorosh]

Canadian Army uses the 60mm mortar one per platoon, in the platoon weapons det. With the belted GPMG. The 40mm grenade launchers (M203) are used two per section (ie 6 per platoon). But the US Army seems not to be that impressed with them in combat operations in Iraq?

[jacobs_ladder2]

Thanks Jon. Very interesting. Fireplanning is something I had always wondered about. So, for example, how far away would you want to be from a 105mm barrage? How much would this vary depending on whatever factors might come into play?

Originally posted by JonS:

</font><blockquote>quote:</font><hr />Originally posted by jacobs_ladder2:

The 50mm mortar for example seems to have been discredited during WWII. Is this true? If so, why?

Well, AFAIK the US Army still has 60mm mortars down to quite a low level (coy?), and 40mm greanade launchers are all the rage at this years fashion shows, so I don't really know that the idea of light mortars is all that discredited.</font>

[JonS]

Originally posted by jacobs_ladder2:

Fireplanning is something I had always wondered about. So, for example, how far away would you want to be from a 105mm barrage? How much would this vary depending on whatever factors might come into play?

If you were;

1) using the L119 (which fires M1 ammo, as used by the M101A1, which was the standard US WWII 105mm Div Arty piece, or a very close relative),

2) firing at a range of 10km,

3) directly over the heads of friendly troops,

the distance recommended is 366 metres in front of the troops. That's made up of a safety distance of 250m, plus an additional 4 x PEr, which at that range is 28m.

For a simple linear target, as generally used in barrages, an 6 gun bty can cover a length of 200m. The same bty, when engaging a 'point' target would spread its fall of shot over an area roughly 150m x 150m - or about a dispersed pn posn.

If the guns were firing parallel (or thereabouts) to the Forward Line Own Troops (FLOT) the recommended distance is just the 250m safety distance (PEr has no effect since it is along the line of the FLOT, and PEd is negligible). The rated lethal distance for 105mm M1 ammo is 40m (rad 40m, dia 80m).

Those are, IIRC, peacetime distances. In wartime, and at the supported arm commanders discretion, the 250m might be dropped to (100m) or (100m + 4 x PEr), or thereabouts.

What would be the difference between a company attacking with mortar support and one attacking without it? And, how much of a difference would it make to have support from, say, 6 81mm tubes?

That's a good question - but ones that's quite tricky to answer. The best answer I can think of is 'it depends', on the ground, on visibility, on the type of enemy, on the degree of freindly force protection (armoured carriers, etc), intel on the enemy, time for preparation, etc. However, in general I'd far rather have the support than not.

Fortunately, you can use CMAK as a test bed if you really want some kind of numerical answer. Set up a scenario with a US Coy with a 81mm FOO with loads of ammo and a couple of TRPs on one side, and a german pn (reinforced, perhaps with an HMG or too, and some trenches) on the other. Then play it several times, and see what happens. Try with and without the FOO, try using only HE, only Smoke, and a mix. Try at night and during the day, etc.

Edit: shameless plug: Halvenboom, available at the Scen Depot, has a somewhat similar situation to that 'test-bed' involving British vs Germans. It is set up for play against the AI.

Regards

JonS

[ March 23, 2005, 06:50 PM: Message edited by: JonS ]

[Wartgamer]

Originally posted by JasonC:

Wargamer still can't wrap his mind around the concept of a larger target, and that firing at 50 infantry fighting positions with 12 guns is much easier than firing at 1 with 1, times 12. The entire error pattern is within a battalion's footprint. The only remaining relevant factor is what portion of the battalion footprint the total area of the fighting positions occupies. See above for actual results of realistic estimates on that score - 1 in 30 hits within 3m, and 1 in 125-150 hits bang on.

JasonC needs to wrap his math around reality. Infantry in defensive positions do not bunch up like he is hoping they will do. They do not spread out in depth like he conjures either.

German defensive works had weapons positions that put field of fire over cover, but would allow access to small bunkers with overhead cover. 'Unterstand' bunkers for up to 10 men would also be accessed. They did this with narrow communications trenches. Infantry under bombardment would get to these positions. The 'footprint' of such a bunker is much smaller than he seems to model and used the lay of the land to further decrease his math. Just using the slightest 'reverse-slope' on the back of a slight rise decreases the hit percentage that 'flat' math calculates.

[ March 23, 2005, 06:54 PM: Message edited by: Wartgamer ]

[JasonC]

Look at any WW II infantry position diagram that includes a scale. Count positions. Measure area. Not hard, I've done it, wargamer obviously hasn't.

[Wartgamer]

German Field Works of WWII, pg 5

[Wartgamer]

Here is an actual battle that was studied in detail. Note that the infantry platoon is attacking. Note its 'footprint'.

[JasonC]

An actual defense system, north of Stalingrad, 1942. Overlooking and defending a balka.

[Wartgamer]

4 MGs per 500 meters? Thats what I see. Lets say its 50 guys holding 500 meters.

It appears to be about a Battalion strength unit overall.

Please tell me what you think you see?

[ March 23, 2005, 07:46 PM: Message edited by: Wartgamer ]

[jacobs_ladder2]

Originally posted by JonS:

If you were;

1) using the L119 (which fires M1 ammo, as used by the M101A1, which was the standard US WWII 105mm Div Arty piece, or a very close relative),

2) firing at a range of 10km,

3) directly over the heads of friendly troops,

the distance recommended is 366 metres in front of the troops. That's made up of a safety distance of 250m, plus an additional 4 x PEr, which at that range is 28m.

So, you know the shell will land somewhere within a very thin rectangle/oval 28m long? The 250m minimum peacetime safety distance, I assume, is just standard practice, but why multiply the PEr by 4?

The rated lethal distance for 105mm M1 ammo is 40m (rad 40m, dia 80m).

The rated lethal distance? Would this mean that anything within 40m, if unprotected, will be a casualty?

Fortunately, you can use CMAK as a test bed if you really want some kind of numerical answer.

Regards

JonS

Not really a numerical answer, but a general idea of the impact of these weapons on the battlefield. I can't see a 50mm mortar, for example, doing much except providing surpressive fire. But honestly, I just have no frame of reference.

What I really need is some way of gauging the kind of punch these weapons packed.

Time and effort much appreciated.

Cheers

Paul

[JasonC]

Force to space ratio for the initial period at Kursk, from Zetterling and Franklin.

North sector, 13th army is deployed on 32 km of front to a depth of 30 km, in 3 lines. 12 divisions within that area. The front line was 4 divisions on 32 km of width by 5-6 km of depth, thus 1 battalion in every area 2 km on a side. Every up km would have a company. But this was thin enough the Germans broke in easily. As the reserves closed up, the Russians had 5 divisions backstopping the location of the single one hardest hit the first day, with much higher front to back compression than at the outset.

Force to space for the push to St Lo -

Diagram of crossing the Vire -

That shows 4 battalions on about 2km by 2km. Notice EFG companies = 2nd battalion, 117th infantry on that forward hill. I get 700m by 1100m for that battalion, with the bulk of it in the forward half of an area that size. The next map shows the positions reached by nightfall, and has 6 battalions on a frontage of 4300m, or 600m per battalion.

That was an opener - here is the first attempt to get on the ridge line overlooking St. Lo proper, on 11 July -

Notice the entire 116th regiment plus 2 battalions from other regiments behind them, in the final positions - all about 1 km on the long axis and more like half that on the short. That is the push along the ridge toward Martinville. Battalion sectors 400m wide with a supporting battalion right behind.

But those show attacking concentration, one might say. Fine, count actual infantry positions in this German defense scheme in the same bocage fighting. Note the scale, lower right - that says 100 yards, not 1000 yards.

[ March 23, 2005, 08:38 PM: Message edited by: JasonC ]

[JasonC]

In the Stalingrad position example, I see 31 MG positions and 64 other infantry fighting positions on a frontage of 5 km, with maximum depth 1 km. Do I have to worry that one of my rounds might land 150 yards long, when I am firing at a target that is 5 km long by 1 km deep? I do not. Do I have to ensure my converging sheaf brackets a single slit trench, or does it only have to land on or near any of 100 fighting positions (or the accompanying open trenches)?

The force to space ratio was not in podunk. Arty works because fronts under threat of infantry attack need to be manned, not thin outposts. And manned fronts mean real targets, not single slit trenches.

[JasonC]

The secondary strongpoint at Dien Bien Phu was called Isabelle. It was a few miles from the main base, defended by a regiment of infantry, and home to a 105mm artillery battalion meant to provide flanking fires against enemy attacking the main position. Its commander was Lt Col Andre Lalande. Bernard Fall continues -

"Lalande had been an artillery commander during WW II and was thus fully aware of the necessity to dig in his troops, and to dig them in deeply. Even ten years later, some of his subordinates recalled that Lalande had called them together before the battle even started and told them 'the Viets have got 105s. You've got to put at least one meter of earth above your heads.'"

[JonS]

Originally posted by jacobs_ladder2:

So, you know the shell will land somewhere within a very thin rectangle/oval 28m long? The 250m minimum peacetime safety distance, I assume, is just standard practice, but why multiply the PEr by 4?

Not exactly. The PEr is a statistical thing, and 4 of them - on either side of the taget - gives you a 95% (or 99%, I forget which now) confidence interval. So, when firing a single gun at a specific target 10km away, you can be 95% sure that - after correct adjustment - it will land in a strip a few metres wide, and somewhere between 116m long or short of the target.

Bunching a btys (or regts) worth of those 'strips' together gives you good coverage over an area 150m x 150m (or 250m x 250m)

The rated lethal distance? Would this mean that anything within 40m, if unprotected, will be a casualty?

Yes, standing, unprotected within 40m = dead.

Standing unprotected within 250m = cas.

Although, that isn't quite right because of the way the fragments actually disperse from a point-detonating round, but it's good enough for planning purposes.

Not really a numerical answer, but a general idea of the impact of these weapons on the battlefield. I can't see a 50mm mortar, for example, doing much except providing surpressive fire. But honestly, I just have no frame of reference.

What I really need is some way of gauging the kind of punch these weapons packed.

And if 'all' the 50mm mortar does is suppress the enemy long enough for the rest of the pn to close and destroy, or holds it in posn long enough to whistle up something of a heavier calibre, then that's a win.

This, from FAS, might help with understanding the effects of artillery and mortars, especially the sections on blast and fragmentation.

As a further guide, here are the lethal and safe distances for a reange of weapons:

Weapon ... Lethal ... Safe

105mm M101A1 ... 35 ... 250

155mm How M198 ... 50 ... 350

81mm Mortar ... 40 ... 250 - 300

5-in Naval ... 50 ... 450

Regards

JonS

[ March 24, 2005, 12:11 AM: Message edited by: JonS ]

[JasonC]

Actually, KZ and CZ zones are 50% lines, typically. That is, you figure out how far from the blast a man standing in the open without cover would have to be, to have a 50-50 chance of being killed (KZ) or wounded (CZ). It is generally assumed different ranges follow typical relations like gaussian fall off or increase as you get closer or farther.

Just lying down, flat, can reduce the exposure by 80-90%. Very close hits get you whether you are or are not taking cover. Even hits quite far away can be dangerous if you try to walk around in the stuff, upright.

Which, duh, people don't. The first salvo sometimes gets coverless defenders, beyond that they generally don't. Not because they sprint 150 yards out of a neat and known blast zone as happens in CM, but just by lying flat and as the men said "crawling inside your helmet".