Fortification Durability Tests

[LongLeftFlank]

In playing around with my CMBN Dien Bien Phu project, I have been trying to see how closely I can replicate the (mostly poorly built) French fortifications in the "entrenched camp" and its various bastions (CRs). These consisted mainly of narrow slit trenches for shelter and communication, connecting sandbagged fighting positions/scrapes, dugouts and a few sturdy blockhouses.

The in-game bunkers are fairly weak: cement or wood doesn't matter much. Because the engine treats them as a kind of immobile vehicle (and their occupants as passengers), they are very easily spotted even in concealment terrain. And their cover values are poor; even small arms seem to penetrate them readily, causing their inhabitants to abandon them even. Steve has rationalized this in the past as these bunkers representing roofed over entrenchments hastily prepared by infantry in the field (as opposed to the more professionally engineered Westwall kind). In which case I'd ask: why include cement bunkers then? and if they're roofed over holes, why is their profile so high? All this also begs the question: when do we get the more durable kind?

Also, CMBN entrenchments offer comparatively poor protection (although better than non-entrenched) against HE plunging fire (mortars), even for units lying prone in them. Simply put, they are too wide (and not deep enough, obviously, owing to the "earth pimple" design FoW compromise). The game does not include narrow slit trenches which render their occupants basically invulnerable to anything but direct hits by small-medium calibre shells.

[LongLeftFlank]

Nonetheless, I have set out to see how I can maximize the survivability of the fortifications we've got by sinking them into the earth and sticking them behind sandbag walls -- effectively placing them in hull down positions. Below is the test scheme I came up with, built on a flat pooltable map (default height 20m) -- I'll work in hills and crestlines later.

Here is what the scheme looks like to an enemy at the same height. Note that I have placed sandbag walls between each bunker and the enemy test shooter.

The sandbag walls also provide firing positions for the trench occupants. Basically, the idea would be to shelter from incoming in the (sunken) trenches and dugouts and then crawl up to fighting scrapes (as shown by the nearest team in the photo) to meet the enemy infantry attack. However, in this test case, they are actually able to spot and engage a distant enemy from the trenches in spite of the 1-2 meter lower elevation.

A platoon of "French" (Canadian and US) paratroopers is deployed in the trenches and bunkers shown, with AI orders to Hide (i.e. not to return fire). This creates a "firing range" situation for the enemy, who is also engaging from a close range location: 210-250 meters.

The next step is to test their performance against various weapons, and then reflect on whether what we are seeing makes sense in the context of the WWII era. I intend to test them with all the direct fire weapons used by the Viet Minh at Dien Bien Phu: flat-trajectory guns, bazookas (shreks), light/medium mortars and machine guns.

[LongLeftFlank]

Let's start with the most lethal weapon: a direct fire high velocity gun. I used a British Airborne 2lber (57mm) AT gun, a highly accurate flat trajectory weapon with HE and AP ammo. I have modded it to look like a 75mm recoilless rifle of the type used by both sides at Dien Bien Phu. Gun crew is Green.

I ran four plays of 10-12 minutes each. The results were similar enough that I didn't see value in running more. I also ran a 30 minute playthrough as the French defenders, and found the results consistent with these tests.

Test 1. Gun spots all 3 bunkers quickly, but does not fire. I order Area fire to a point beyond each bunker.

1.(left bunker, 215m). Area shots 1-2 penetrate, shot 3 sets it afire.

2.(centre bunker, 230m) Area shots 1-5 overshoot, shots 6-8 penetrate (bunker KOed).

3.(right bunker, 250m) First Area shot sets it afire. This is a cement bunker!

Bunker 1

Bunker 2

Bunker 3 (revetted 3 meters below the range -- a 4 meter depth would put it out of sight of the shooter).

Test 2. Gun spots bunkers 1 and 2 immediately and fires on 2.

2. 5 shots in 1 minute -- all penetrate and shot 5 KOs.

1. Area shots 1-2 penetrate and set afire.

3. Never spotted - 5 area shots do not reveal it.

Test 3. Gun spots bunkers 2 and 3 within 30 seconds. Order Area fires

3. Area shot 1 sets afire

2. Area shots 2 and 4 hit - KO. others overshoot.

1. Never spotted.... I didn't bother trying area fire

Test 4. No area fire or other commands needed.

2. Gun spots immediately, KO'd in 2 shots (all penetrate)

1. Gun spots in minute 2, KO'd in 4 shots (all penetrate)

3. Gun spots in minute 3, KO'd in 4 shots (all penetrate)

And here is a surviving French para, stunned at how easily his "cement blockhouse" was destroyed and set ablaze. Note the Kilroy graffiti visible through the door.

EARLY CONCLUSIONS:

Just reconfirms what we already know; bunkers are virtually helpless against flat trajectory guns, even of lighter calibres, and are knocked out very quickly. Putting them in hull down positions does nothing to extend their lives -- even bunker 3, whose roof is the only part visible was killed instantly. Their firing slits are not their weak point (like you'd expect) -- they get killed just as quick from behind or the sides.

The only protection seems to be to hide them deep in the earth (4 meters) or behind crests so they aren't visible from a distance.

[LongLeftFlank]

My second test used a 2 Inch British Airborne light mortar, representing the homemade, Japanese and prewar French weapons in the VietMinh arsenal

This weapon took 4 ranging shots on the closest bunker (215m), then hit it with all 8 of its remaining rounds, but caused no casualties to occupants. I discontinued testing at this point; I will try again later with a US 60mm (which was used by the VietMinh).

[LongLeftFlank]

Here's the one you've been waiting for, hot off the presses.

My third test used an 81mm British Airborne medium mortar team (Regulars) with a forward observer (Vet)

Test 1. Area fired on bunker 2 site (never spotted). 4 ranging rounds then 9 of 23 shots hit, KOing bunker and killing occupants

Test 2. Indirect fired on 2. 2 ranging rounds then 9 of 27 FFE shots hit, killing 2 of 3 occupants.

Test 3. Direct fired on 2. 5 ranging rounds, then 10 of 22 shots hit, killing all occupants

Test 4. Direct fired on 2. 4 ranging rounds, then 8 of 23 shots hit; 1 occupant lightly wounded

Test 5. Direct fired on 1. 4 ranging rounds, then 8 of 23 shots hit, killing 3 of 4 occupants

Test 6. Direct fired on a 30 meter segment of trench, "walking" target along trench (red X's in photo); 4 ranging shots, then 10 of 23 shots landed in trench, killing 7 occupants

Test 7. Direct fired on a 40 meter segment of trench, "walking" target as before; 3 ranging shots, then 8 of 24 shots landed in trench, killing 7 occupants.

I also ran a couple of plays playing the French side; the VM mortar failed to shoot at my forces unless I UnHid and took some pot shots first -- it then fired a few rounds in reply and fell silent again.

EARLY CONCLUSIONS:

a. The bunkers seem to provide reasonable protection against mortar fire; a lot of the casualties are taken through the firing slit (it would be nice to have one that's just an all round shelter). 27 direct fire shots under ideal conditions is pretty heavy punishment.

b. The trenches provide very weak protection against mortar fire; again, 27 81mm shells is an intense barrage on a small segment, but it consistently caused 50% casualties to the (Hiding) men under it. That's higher than I'd expect for men in trenches. I'll rerun the test a few more times to reconfirm the results. Not sure what I can do to mitigate this, other than to stick the men in revetted bunkers (dugouts) along the trench line and exit them once the barrage lifts.

c. Once they range in, mortars seem to land at least 30-40% of shells right atop a point target; this is fairly consistent.

[John Kettler]

LongLeftFlank,

It's going to be an awfully short siege! Right now, in terms of game pieces and systems, you appear to need a hybrid of CMBO (would give you M24, 57 and 75mm RR, 75mm howitzer, 105mm howitzer, good bunkers, PBs, trenches and such outright), plus CMBB (reworked MG handling). Obviously, you can't do that, but in those, a trench really counts for something, and bunkers and PBs take real work to defeat.

What you've produced is wonderful in terms of visuals (especially like the French camouflage, which closely resembles some Portuguese cammies I used to have), but I don't know what to even suggest in terms of how to make all that you've done (in aggregate, doubtless tons--scenarios, OOB, research, playtest, etc.), work as you need it to in depicting DBP. And the only time I saw concrete bunkers or PBs burn in CMx1 was following a flamethrower hit.

Mortar lethality is simply ridiculous. And while it's certainly higher than field artillery against men in trenches, it's ludicrous, as I shall prove.

During the Cold War, the Bundeswehr ran Soviet style artillery lethality tests on what I recall as a defending platoon target, represented by appropriately posed plywood mannikins. Using a scale of fire (destruction) for Soviet norms, the baseline was the annihilation of the exposed platoon. Adding foxholes dropped the losses to 30% using the same weight of fire. If overhead cover was provided, the number dropped to 10% of the baseline. To put the numbers into perspective, 30% is bad enough to temporarily incapacitate the unit long enough to overrun it. I believe it would be combat ineffective for an hour or more. That would meet the Soviet neutralization criterion. 10% would suppress the defense temporarily (again, a Soviet threshold, suppression), allowing attackers to close while the bombardment continues, so against Soviet style Cold War bombardment levels, even foxholed troops with overhead cover would still be suppressed!

I think the above form a reasonable baseline for evaluating your plight. The above tests were done with far more lethal weaponry than typically was the case during WW II, thus, overstate the likely outcome using the weapons circa DBP.

With that as the upper bound, let's look at the pertinent WO studies John D. Salt so kindly provided us.

http://mr-home.staff.shef.ac.uk/hobbies/ww2eff2.pdf

"WO 291/946 Effects of bombardment – present state of knowledge.

This summary was published in 1946.

If firing 1000 25-pdr shells into a 300 × 300 yard box with 100 men in it in slit trenches, the expected number of casualties would be nine."

1000 25 pr rounds vs 100 men in slit trenches = 9% casualties

Granted, these aren't mortars, but the lethality, relative to the Cold War Soviet baseline, is down already by a factor of more than three.

Now, let's look at what the same study has to say about bunkers and PBs. This speaks directly to what ought to be seen vs what you're getting for results.

"If the enemy is in protected positions such as pillboxes or concrete gun casemates instead of in open positions the state of affairs is different. No projectile which cannot pierce the protection has any noticeable effect. The neutralising, morale and lethal effects do not exist until the material effect is achieved."

WO 291/107 Comparison of the 71⁄2lb and 10lb 3" mortar bomb.

"The chance per round of knocking out a point target is found to be approximately 1 in 16, so that after 20 rounds against an unprotected point target 70 per cent of the men present would have become casualties."

So, if we fire a 3' mortar at, say, an MG nest in the open, 20 rounds will somewhat exceed the earlier 60% neutralization criterion (70% vs 60%). The previously referenced 25 pr 1000 round shoot got 9% against infantry in slit trenches, and our Cold War shoot found foxholes dropped bombardment casualties by 70%.

Restated, to a first order, the VM mortars should be causing no more than .7 (initial lethality) x .3 (adjustment for foxholes) = 0.21, against a single entrenched MG team, per 20 rounds expended. Thus, what you're seeing is somewhere between ~ 2-2.5 x higher than the analysis predicts. That's before factoring in the the terrain!

WO 291/138 Influence of ground cover on performance of HE projectiles.

The scale runs from I Very Poor (sandy beach), Cover Index 1-1.5 through V Very good (Ground with anthills, or strewn boulders; freshly ploughed land; old tank park) Cover Index > 4. These are explicitly for the 3" mortar. They'd be much worse for the 25 pr because of projectile angle of descent and effect on frag pattern.

Let's now factor in the cover effects. If we postulate the cover index as a very VM favorable 1.25 (early in the battle, trenches in pretty good shape), then I think we're looking at another lethality degradation of 25%, reducing the 21% Pk (for 20 rounds against the entrenched MG) to ~16%. If, though, we presume the lunar landscape which rapidly developed during the siege, and set the Cover Index at 4, it now becomes a Pk of ~5.3%

So, the reasonable best case for the VM in the 3" mortar shoot would appear to be ~16% Pk per 20 rounds expended vs one entrenched MG. Thus, the best case, using the 40% casualty number you provided and the cited WO excerpts, is that those losses are 2.5 x more than this analysis predicts. The worst is that that the high end 50% losses you provided, when compared against that same MG nest in very good cover, are 9.4 times higher than what this analysis predicts!

Nor does this analysis reflect a factor of 6 decrease when men go prone in any kind of bumpy terrain. This is in reference to some AORS test I saw cited in the WO material but can't find now.

To say VM mortars are overperforming in your trials would be well past British grade understatement.

Since I haven't done a set of calculations like these in a long time, I may've erred somewhere, but the answers do feel right to me. I'd further add that I belatedly noted you used a Veteran FO. According to what I read, the only FO's the VM had were so bad they had to calculate data all day, so as to shoot at night, and were exclusively for their only indirectly fired asset, the 105mm howitzers.

------------------------------------------------------------------------------------------

Conclusions

1. Barring direct penetration of the bunker or PB, it should be effectively immune to bombardment and its occupants safe. Offsetting this are two factors: a) French lack of fortification materials (recall as something like 3.5 vs 21(forget metric) needed) and worsening soil load bearing capacity as rains set in. Combined, we know at least one bunker collapsed as a result.

2. Mortar fire lethality, vs a single entrenched MG, is 2.5-9.4 times higher than the analysis predicts.

Since there's only so much you can do to harden the positions, you may have to design for effect by tweaking the men to give them the resilience their positions can't. Unfortunately, they're still going to take wholly unjustifiable casualties, despite being able to bear up under the bombardment.

Regards,

John Kettler

P.S.

In doing DBP digging recently, I saw something on the towed Quad .50s there. Per what I read, the French had enormous amounts of ammo, effectively unlimited, and kept one such mount (near the Bailey Bridge, wherever that was) in action to the very end. To my knowledge, the Maxson towed quad mount isn't in the game, but the French could really use equivalent firepower.

[LongLeftFlank]

Good post, John, thanks. I guess the question that springs to mind at once is: is the overmodeling in my tests a function of the idealized firing conditions? -- i.e. the shooters are able to sit in a secure position at midday and bombard a target set 200-250 meters away with impunity. As many real world mortarmen have attested here, given firing range conditions, they can drop "a pickle in a bucket" firing direct at ranges up to a km. And a high velocity cannon is like a sniper rifle at that range.

So if your data (or some other data) represents the expected real world outcome (design for effect benchmark), does changing the firing conditions -- increasing distance, lowering visibility, allowing counterfire, etc. shift the results toward the benchmark?

[LongLeftFlank]

But before readers simply dismiss these tests as a triviality, keep in mind that for about 5 weeks following the "Five Hills" battle, the Viet Minh were able to emplace direct fire weapons (mortars and RCLs) in overwatch over the French positions (at equal or higher elevation), at ranges of 250-300m, often less! While they had to contend with vigorous French counterbattery fires which confined their intensive operations to nighttime, it is also well documented that their presence made daylight movement very hazardous for the defenders.

However, even under such close conditions there is no record of them blasting the French out of their holes. The purpose of the bombardments was to suppress the defenders to support infantry assaults, not to annihilate. Which it could not accomplish against even primitive entrenchments, even using many guns firing hundreds of rounds into small areas.

[c3k]

Nice.

My understanding of bunkers (both types) is that they provide distinct zones of protection based on height above floor level. Meaning, troops "up" are much more likely to get hit than troops hiding on the floor. Realistic? Um, no. But, it does "model" the weakness of the large opening shown on the bunkers.

Ignore mortar (over)accuracy for now.

Based on your test:

Bunkers give GOOD overhead cover. That seems correct.

Bunker spotting is odd. That is due to how they are programmed in the game. Nice to be fixed.

Direct fire shreds bunkers. That seems correct. There is room for improvement, vis a vis penetration and resistance of specific rounds and bunker types and location of the hit. Overall, if you're in a bunker and a tank rolls up, you're in a world of hurt. (Exceptionally well-built concrete fortresses were not as vulnerable. They are the exception.)

Bunkers burn. Huh. Did each of your bunkers include ammo? Grasping at straws with that one. I would think it should be hard to ignite a bunker. Harder, at least, than a building. (Civilian buildings would, IMHO, ignite more readily than a bunker.)

Thanks,

Ken

[Sgt Schultz]

It seems to me that you will need to bury everything below grade level, and still reduce ammo allotments and calibers available to the VC.

CM-land is a land of compromises, and you found another my good man. I tried "burying" buildings with the roofs removed. That sucked too, as their integrity is severely compromised once they lose their roofs.

EDIT - Damn Photobucket has changed. My pics are reduced to thumbs. Sorry

[LongLeftFlank]

My screenies are also on Botophucket, but yeah they changed it. Now, when you go to your "library" (fka "album"), left click the little gear wheel that appears in the top corner of each thumbnail when you mouse over, then you'll get a popup -- pick the linky that says "Get media links". That'll give another popup with the img data to copy-paste over.

C3K, I have yet to see the occupants of a bunker Hide (or take cover on the floor) other than while Cowering as a result of incoming. Or is the wireframe visual just not showing something that they're really doing? That's good to know, if true.

I can certainly sink the bunkers 4m down out of sight, and if their purpose is shelter from shells (not fighting positions), also cover their vulnerable vision slits with high stone walls or hedgerows.

[c3k]

Hide: you have to command it. That _should_ reduce vulnerability. (All this is based on memory... If I'm wrong, I apologize.)

[John Kettler]

LongLeftFlank,

You're welcome! I had no idea, having not read Fall since high school, the VM were able to get so close. In the earlier stages, per my limited understanding, weren't the VM on the forward slope of the first range of hills, set much farther away than what you ran in the test? That would certainly help, at least, until they closed.

To my mind, the two most dangerous weapons the VM have, as far as sheer killing power, are the 105mm howitzers and the Katyusha (U.S. rockets as substitute?), the latter a proven bunker killer later on in Vietnam (details and pics in the CMBB Katyusha thread), able to slice through even the heaviest sandbag protection with ease. Our exhaustive analysis at the time concluded the Katyusha was somewhere between a 122 howitzer and a 152mm howitzer in terms of effect, so these would obviously exert a lot of leverage. That's before looking at the volume of fire per unit time and the associated morale effects.

Working from memory here, if the VM had, say, 12 of the 6 tube towed launchers for which I provided a pic in your main thread, that would correspond to 1.5 Katyusha batteries (6x BM-13, 12 rails per), which at this scale, would be awful on the receiving end. In practice, I believe that number was more like 24 such launchers, or a BM-13 battalion (3 batteries)! And these are firing directly, not, as the Russians would say, from covered positions.

The VM have 14 x 105mm howitzers, making either a battalion+ (12 +2 extra) by WW II U.S. infantry division TO&E, or a battalion minus (need 18, but have 14). Either way, seriously attention getting and well past what we typically see in CMBN fights. That's only part of the story.

The VM have essentially unlimited ammunition to operate those weapons, though probably more constrained for the BM-13, since the projectiles are big, bulky and heavy, compared to 105 ammo. Even so, the BM-13s would have multiple reloads, rather than one and done.

Giap didn't have the 105s in play throughout the battle, though. He didn't use them until a critical point in his battle plan, for which you know the date. Prior to that, if you're using the history, I guess there'd be no FO, thus no 105s.

I think, to a first order, at least, you theoretically can derive the scales of fire, from which, using the right WO study, you can determine whether or not the resulting bombardment would yield a particular level of effect, using computations derived from Western Europe operations. I'd say, though, given their apparent level of technical expertise, the VM would have to deliver considerably more than this to get the same level of results.

Offsetting this is that most of their firepower is direct, not indirect, and the Western Europe calculations are for indirect fire. The Russian view of direct fire effectiveness is that it's 10 x as effective as indirect fire, and that's a consideration. Also, flat trajectory fire is nowhere nearly as good against entrenched troops as is the higher angled indirect fire. No idea what the graze angle is for your representative direct fire RR case (was that a 2 pr or a 6 pr as the 75mm RR substitute? Believe I've read both in the other thread and have gotten confused), but I suspect the angle's pretty shallow, thus offers a poor look into the trenches. I think if BFC's going to force us to live with current physical trench modeling, it should greatly increase the under the hood saving throws for their occupants when fired upon, whether directly or indirectly.

The bunker and PB situation is most unfortunate, but I have a suggestion which might help. I noticed, in reading a thread on buildings as cover, that some scenario designers have figured out how to beef up buildings by wrapping them in a low brick or stone wall, providing virtual immunity to small arms. I, like Sgt Schultz, was going to suggest burying a stout house, both for protection and capacity, but maybe wrapping a bunker or PB would give it something resembling reasonable survivability against DF threats, since the roof, in your view, seems okay already. Might not be pretty, but your bunkers, even allowing for French fortification materiel shortfalls, seem to be highly vulnerable to exactly the most common threat they need to be able to withstand. May I also suggest seeing how things stack up against a 75mm pack howitzer and/or some stand-in for the 75mm field gun?

Since there are no computations here, I'll close this post. Let me know if you'd like me to look into other aspects of the VM threat to DBP fortified positions. I shall be most interested to learn what JasonC thinks about all this.

Regards,

John Kettler

[Sublime]

Well Schultz's fortified houses are really sturdy. Maybe instead of using the actual bunker you could try MG teams in a heavy stone building chopped to one story. or two stories sunken.

But one story with a low stone wall gives significant small arms protection. HE? Good amount, but not so much. Kinda a quandry your in.. FWIW..

edit: well looking at schultz's post I realized the roof missing would hurt the survivability. What about a 1 story, with roof, and you mod the graphics so it looks like a bunker?

[John Kettler]

LongLeftFlank,

I fear I flubbed the calculations into BM-13 battery equivalents, but now, can't undo what I wrote. 12 x 6 tube towed launcher would be 72 tubes. Dividing that by 16 (1 x BM-13 load) = 4.5 BM-13 equivalents = 1 BM-13 battery equivalent(+) additional 0.5 BM-13 launcher. I think I got that right. Thus 24 towed launchers x 6 tubes = 144 tubes = 9 BM-13 equivalents = 2 BM-13 batteries + 1 launcher. Thus, you have a total Katyusha force equal to a BM-13 battalion(-).

Would someone with a sharper brain please recheck my math? I botched it once, so might well have again.

Regards,

John Kettler

[John Kettler]

LongLeftFlank,

So we have some idea what to suggest as a bunker replacement, could you please provide the capacity of the typical French ones at DBP? I realize the main command bunker would be considerably larger than that, but I think knowing the typical capacity would likely improve the utility of the recommendations we're making.

Sublime,

It's too bad we don't have something like our old friend, the small CMBO heavy stone house, available. That, I think, would probably fare better than the current CMBN bunkers seem to be doing. Here's what I'm talking about.

http://dhcwargamesblog.files.wordpress.com/2012/07/normandy_schrek.jpg

Regards,

John Kettler

[LongLeftFlank]

John, sweet Jesus, I give you an inch and you take a mile. You're now flooding a second thread of mine with wordswordswords and any response I write to you is iust going to elicit another torrent of verbiage. Let me try to be nice -- stand down for a while, please. Your comments are no longer helpful even though you think they are.

Briefly: the 105s were deeply buried and with tightly restricted fields of fire played little to no role in bombarding the "femmes" (maybe the first two) -- they shut down the airfield and hammered the main camp. Same thing for most of the 75 guns. The katyushas only came in at the very end. The bombardment weapons used in the fights for the perimeter CRs were the ones I am testing -- mortars up to 120mm and RCL guns. So voila! all those words you posted aren't relevant. And I don't care about the quad 50s either since the Vietminh didn't use them in bombardment which is the point of this thread. The only one.

And you have limited experience playing CMBN, by your own admission, and none at all with scenario and map design. So I fail to see how giving you bunker specs is going to help you "make suggestions" that are useful to me.

Please show some self control by not responding to this explanation, which is as civil as I can make it.

If you are determined to sound off on Dien bien Phu for pages upon pages upon pages you really should read Martin Windrow's book "The Last Valley", which has IMHO displaced Fall as the definitive history of the battle. It contains much of the grog detail re weights of fire you're trying to reverse engineer at length here. Get it via your local library.

[Sgt Schultz]

I can design structure combos that will be almost impervious to direct fire and blast/shrapnel effects, at least until they get worn down.

Making anything withstand even 81mm direct hits from above is problematic at best. The best results I have found for troop survivability over the length of an average 105mm barrage is Hiding on the bottom floor of a Tall Stone/Brick wall-wrapped three-story multi-tile(important!) Modular.. that HAS its roof(at least to start).

So, if you want me to show you how to bury a three story house and still have grade-level access, let me know. It can be done. Modulars rule.

Then place sandbag walls around THAT, with a low stone wall wrapping THOSE.

The iterations can continue until the desired effect is achieved, or maximum ridiculousity.

-

[slysniper]

wow, it just blows my mind that you have figured out a way to get sturdy protection by this much manipulation of what the map maker presently supplies. Nice Job, but it would just be nice if they provided us some tougher options for use in the system.

I can design structure combos that will be almost impervious to direct fire and blast/shrapnel effects, at least until they get worn down.

Making anything withstand even 81mm direct hits from above is problematic at best. The best results I have found for troop survivability over the length of an average 105mm barrage is Hiding on the bottom floor of a Tall Stone/Brick wall-wrapped three-story multi-tile(important!) Modular.. that HAS its roof(at least to start).

So, if you want me to show you how to bury a three story house and still have grade-level access, let me know. It can be done. Modulars rule.

Then place sandbag walls around THAT, with a low stone wall wrapping THOSE.

The iterations can continue until the desired effect is achieved, or maximum ridiculousity.

-

[LongLeftFlank]

I refined my 81mm test vs infantry in trench test as follows:

A single 81mm mortar team (Regular), direct Area firing on a 30 meter straight line of trench sunk 2 meters into the (Damp) ground containing 10 Canadian paratroopers ordered to Hide

Test 1. 4 ranging shots, 7 of 23 hit in trench, 6 killed

Test 2. 3 ranging shots, 8 of 24 hit in trench, 5 killed

Test 3. 5 ranging shots, 10 of 22 hit in trench, 5 killed

Test 4. 7 ranging shots, 7 of 20 hit in trench, 9 killed

Test 5. 5 ranging shots, 10 of 22 hit in trench 6 killed

For tests 6-8, I took the height of the trench to the same as the rest of the map. Rifle (area) fire from the mortar team may have inflicted additional casualties.

Test 6. 4 ranging shots, 12 of 23 hit in trench, 10 killed

Test 7. 4 ranging shots, 11 of 23 hit in trench, 10 killed

Test 8. 3 ranging shots, 7 of 24 hit in trench, 7 killed

For tests 9-12, I sunk the trench 2 meters again and added tiny rubbled barns (as shown) along the rear of the trenchline to see if it would provide additional cover

Test 9. 3 ranging shots, 7 of 24 hit in trench, 7 killed

Test 10. 3 ranging shots, 6 of 24 hit in trench, 7 killed

Test 11. 0 ranging shots, 12 or 27 hit in trench, 9 killed

Test 12. 3 ranging shots, 10 of 23 hit in trench, 9 killed

CONCLUSIONS:

1. In these tests, an intense barrage (average of 10 x 81mm HE rounds achieve direct hits on a 30m stretch of open trench -- creating a large explosion every 3 meters!) is routinely and consistently annihilating most of the target infantry -- casualties average 70%.

Which I suppose I expect, given that the victims are lying in a broad (2m wide?), shallow (<1m high) trench, where they are exposed to near miss shrapnel as well as direct hits, as opposed to a narrow (1m?), man-deep slit trench (not provided in the game). I'd still expect devastating casualties to infantry in slit trenches exposed to this intensity of bombardment, but at a guess it's more like 1:4 or less killed or maimed by blast and shrapnel, with others still able to fight even if debilitated by concussion, shock, bleeding eardrums, terror of being buried alive, etc.

I accept that a trained mortar team (regulars) could readily achieve a ratio of 1:3 direct hits while walking fire down a broad (2m wide?) trench, under the firing range conditions provided here -- short range, midday, firing with impunity. I doubt though that they could achieve the same results against a slit trench if they couldn't eyeball its exact position.

So it doesn't seem to me that the mortars are mismodeled; it's the poor bloody infantry that are deprived of proper holes to hunker down in. FWIW, I'd also expect a significant (10%?) dud rate for mortar rounds impacting in the Damp earth.

2. Sinking the trenches does help survival a little (it also protects from small arms incoming).

3. The proximity of rubbled buildings provides no additional benefit.

So it looks like my trenches are going to need to contain plentiful bunkers, deeply revetted into the ground to avoid being spotted, where the infantry will deploy initially and then leave to take their fighting positions once the barrage lifts.

My next set of tests will refocus on performance of said bunkers under both 81mm and 120mm mortar fire. Out of time tonight, but I'm wondering whether putting the bunkers under trees might help. The key question being: do airbursts impact the infantry in the bunker?

[Sgt Schultz]

Yes, trees can help quite a bit LLF. I have done those tests. Not in your empirical fashion with note taking, but I have slapped enough of my test structures with enough different kinds of arty to get a feel for what works and what won't. The main branches absorb incoming until they get blasted away. You lose leaves, then branches, then trunk. Single Tile Modular, sunk in the ground and surrounded by Three Tree tiles gives most Tree-related cover. Multi-tile Modulars gain inherent strength but lose overhead cover to direct hits for the center tile. I forget which species offers best cover. I think it was 'A' Trees.

A direct hit by 150mm will vaporize a tree. Instant mulch, not even a stump. 81's will gnaw it. 105/120 dissolves the leaves and branches rather quickly.

Deep Forest Tiles(yes they help), with concrete shelters, sunk in the ground, surrounded by three-tree tiles, with trenches leading directly from the doors into the network, which is also below-grade, with interspersed buried Modular structures in sufficient numbers to decoy any human opponent from barraging them all.

Have I missed anything? edit --- yes I did... sandbag and/or low stone walls around the whole magilla. Bocage works as well to soak up blast effects of near misses. You want as much "stuff" on a tile as possible to soak up damage that otherwise would be expended on your precious pixeltruppen.

Somehow we wandered away from DPF to the Hurtgen Forest. I could just send you my map in progress and let you copy the trenches.

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Were there any trees left at the stage of the battle you are talking about? I thought the battle pretty much defoliated the place.

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Between you and DPF, and ian and his flooded roads, I am having more fun figuring out other people's issues than working on my own maps.

[Sgt Schultz]

Here are some ideas you may wish to try. Remember, these were taken before I learned that removing a roof screwed a building's integrity.

[LongLeftFlank]

Great stuff, very ingenenious, although it looks a little too large and elaborate for my purposes. Thanks for the info on the trees; you are right that the various redoubt hills were deforested to clear fields of fire (and to provide raw materials for fortification which were in short supply).

The problem I've found with walls and hedgerows is that, like trenches, they are in the centre of each square so trenches cannot sit in close proximity to them, which negates a lot of the benefit.

Another "cheat" that's occurred to me is to have most of the defenders appear in the trenches as reinforcements following the initial barrage (as if exiting underground shelters not explicitly represented in game. If the barrage is intense, they can appear with Weakened fitness, lowered headcounts and reduced morale state. I'd rather not resort to this though, since to me a key part of the DBP "wargaming experience" is being "in the boots" of your poor copains as the Viets rain hell on them then assault the wire.

[Sgt Schultz]

Now these may not apply either, but the concepts should be valid.

By placing walls inside rubble, you get a little extra splash damage protection, at the cost of movement silliness that must be rigorously tested out.

You want immunity to indirect fire??? Say hello to my leetle friend.... the immobilized sunken TigerPit bunker. Drop all you want on him, he won't care a whit.

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While writing this, it occurs that I have never experimented with sunken, immobilized Half-Tracks.

Throw a few rounds at some HTs sited along your trench lines LLF. Maybe they will help some.

EDIT --- StuG, JPzIV and JagdPanther would represent bunkers in a more realistic fashion, with their small fire arc.

[LongLeftFlank]

Well now, Comrades Minh, Nguyen, and I wait until nightfall and then leap out of the halftrack and take the French by surprise!