Gamey or Real, approach to taking out fortifications..

[sgtabell]

Hey all,

Something I noticed. I won't go into specifics, but want to know what the grogs think.

Using Biltong's Awesome Rules for Grog Wannabes, I was performing an attack. I ran across a fortification, (75 mm gun I believe, concrete), and noticed that my IIc did a fantastic job of getting slit penetration. Obviously this is due to number of shells in a firing, vs. the other two tanks that were firing at it. I went back and replayed the turn, and set up something with scenario editor.

So I know this is due to high number of shells hitting the slit, and is there any evidence to this actually being a technique which was found to be useful?

SgtAbell

[Gaylord Focker]

To ko a tiger, your going to want to try fast flanking manuvers with a diversion up front.

[Redwolf]

I have never come across a historical reference that smaller guns are more effective against concrete bunkers than bigger guns.

I was surprised that BFC didn't address this issue in CMBB.

[Silvio Manuel]

I would think that it goes without saying that an auto-cannon like a 20mm would be far more effective than a single shot cannon of any caliber. How many 20mm need to get thru the slit before the crew is turned into chunky salsa?

IIRC, they DID address this in CMBB, but I'm at work so I can't check the readme file or manual.

SM

[Zarquon]

There was a forum thread about this a few days before.

http://www.battlefront.com/cgi-bin/bbs/ultimatebb.cgi?ubb=get_topic;f=23;t=006342

[JasonC]

"it goes without saying"

Code for "when pigs fly"

"that an auto-cannon like a 20mm would be far more effective than a single shot cannon of any caliber."

Horsefeathers. There are recorded historical AARs of 155mm single shot cannons taking out a bunker with every round. There are no WW II historical AARs that I've ever seen, or that have ever been presented on this subject, of bunkers actually taken out by tiny caliber auto-cannons.

It was a useful tactic to fire large caliber guns at the firing slits. The usual result was to pin the men inside the pillbox after a few rounds. Not to KO the pillbox or actually hurt the men. There were elaborate pillbox killing procedures and weapons, like demo charges and flamethrowers, precisely because firing slit shooting did not destroy them.

"How many 20mm need to get thru the slit before the crew is turned into chunky salsa?"

A lot more than one tank carried, that is certain. The blast from such tiny rounds was non-existent. It essentially had to hit a man on the fly, like any machinegun. If 20mm KOs pillboxes in seconds, why don't MGs? They've got even more rounds looking for the firing slit.

The reality is the firing slit was a tiny target to begin with, typically angled to cause ricochets rather than "flat". Men manning actual weapons formed a tiny portion of the cross section of even the firing slit gap. Even if one were directly hit, it did not mean the pillbox was broken like an eggshell and all the people oozed out.

The problem is simply that CM using a "vehicle" model for bunkers. The same armor penetration and behind armor effects categories are used. The firing slit is treated as a portion of the front, like the chance of a gun hit on a tank. But pillboxes have no moving parts to damage. Rounds only hurt them if they hurt the men inside.

You should see occasional pins, very occasional -1 crew and pin, from hits on the firing slit from small caliber guns. It should take sizeable blast to actually KO most of the men inside. Right now, the men are often better off inside a trench than inside a concrete pillbox, simply because the former uses the infantry combat model and the latter uses the vehicle one. Which is absurd.

[tar]

I second JasonC's opinion.

Having pillboxes (and also wooden bunkers) be a bit more durable would also enhance the usefulness of specialist weapons such as flamethrowers. One of my contentions about why flamethrowers are less than useful in most CMxx battles is because of the absence of really tough fortifications. Even fortified infantry is too easy to take out by generaly firepower means, so that the flame weapons which were historically the most effective counter to the fortifications are not needed. And given their fragility, they are very hard to actually apply.

[lcm1947]

I remember reading that it took like a 150MM cannon to take out a bunker and then it wasn't that it blew it up but caused the men inside to surrrender due to the shock, noise and terror. Can't remember the book but it was only a couple of months ago that I read it so remembered it.

[Hat Trick]

There are two ways that bunkers can be considered to be too strong/powerful/effective, rather than undermodeled.

The first is the issue line of sight. One of the reasons that large caliber high explosive rounds can be effective against bunkers is not the damage that they cause, but the amount of smoke and dirt that they throw up in front of the vision slit, temporarily "blinding" the occupants. The ability to see through a large artillery barrage, even if not directly on top of the bunker, is very limited in real life (so I’m told). I do not believe that this effect is modeled in the game.

Additionally, concrete bunkers are invulnerable to damage from artillery, as best I can tell. I did a test some time ago in CMBO, and found that even 14-inch battleship guns didn't affect them. Multiple direct hits, not even a "pinned" reaction. While I believe that most indirect fire would cause little damage to (well designed) concrete fortifications, I doubt that any above ground structure would be able to withstand this type of blast.

[Redwolf]

I think the root of the problems is that the penetration through the firing slit is treated like a penetration to a tank.

In the tank you have internal parts of the steel flying around along with the shell. It is extremly cramped, whatever is flying around likely hits somebody or something. You easily hit hydraulic pipes, causing fires. Comparably tiny explosions cause the ammunition to cook off. You can hit the fuel tank, the engine or the gearbox, all of them may instantly start burning.

None of that applies to pillboxes in real life, but CM treats them the same way. Except that the pillbox has a large firing slit so that the penetration is easy to achive with any high-ROF gun. But in reality such a penetration would be far more harmless than it is in CM.

[Affentitten]

Originally posted by Hat Trick:

The first is the issue line of sight. One of the reasons that large caliber high explosive rounds can be effective against bunkers is not the damage that they cause, but the amount of smoke and dirt that they throw up in front of the vision slit, temporarily "blinding" the occupants.

A standard procedure when dealing with Japanese bunkers in the Asian war was to wheel up a two-pounder or Bofors and just fire at top of the slit with the intention of caving it in. It wouldn't cause much damage to the occupants, but they wouldn't be able to fire back, allowing them to be outflanked and receive a doorknock at the rear.

[Guest Mike]

I read somewhere that to actually reliably penetrate a firign slit you had to be quite close - 250 yards perhaps.

Australian and New Zealand Valentine and Matilda tanks in the Pacific theatre were equipped with HE precisely to get the firing slit penetrations. Armour meant hey could get close enough.

Large calibre guns could do significant damage from a longer range because of the weight of the shell and explosive effect (most bunkers could be penetrated by a 5.5" HE shell), and IIRC there was a sort of short range rocket consisting of a 250lb bomb fitted to a 5" rocket motor and fired from a trough that was used a bit too.

edium calibre field guns (25 pdr, 75mm, etc)weren't so useful because they weren't heavy enough to penetrate from longer ranges or from the side, and bringing them to within 250 yards of the front of a bunker slit was a bit risky.

I don't doubt that repeated penetrations of firing slits by autocannon would have done a lot of damage - Jason's protestations notwithstanding there's also the weapon inside that can be hit.

However I think such peentrations should be rare beyond 250 metres - so if you want to bring your P-2 that close feel free to try to get away with it!!

However I suspect that 20mm guns weren't often in a situation to be used for such a purpose (indeed the alies simply didn't use 20mm autocannon at all for field forces much) and hence we don't read about it often because it didn't happen often.

[JasonC]

Firing AP at a bunker to pin the men inside, for others to approach, was SOP in many armies, whether against Japanese bunkers or anybody else's. But it pinned the men, it did not destroy the bunker. That took other weapons.

Yes large caliber HE could and did destroy many bunkers when a direct hit was obtained. A typical *log* bunker was built to withstand an overhead direct hit by 105mm HE. But a larger caliber HE hit would destroy them. That cannot be said, however, for the toughest concrete pillboxes. Even 155mm. Even at rear doors.

The comment that we don't hear about it simply because nobody brought 20mms strikes me as a little daffy. Everybody brought 50 cals. Don't they go through the firing slit even more often than 20mm rounds? And if it was so effective, why *didn't* they notice and bring such weapons along?

Meanwhile, it also just isn't true - both Russians and Germans used 20mm autocannons as main armament on light tanks. Why didn't they report their wonderful bunker busting properties? Why all the elaborate provision of Brummbars and flamethrowers and demo charges, is a Pz II at 500 yards was all you need?

One mentioned the 250 lb demo charges thrown from some Brit "funnies". Why the bother, if any ordinary tank with an ordinary 75mm HE would certainly find the slit with a minute or two of shooting, from even farther away? Were they just stupid?

There are Russian reports from the winter war of taking out Finn concrete pillboxes in the Mannheim line successfully. Did they just stand off at 250m and shoot 45mm rounds into the slits? Um, no. Yes, they used direct fire by guns or tanks to drive men away from the embrasures - to pin, in CM terms. But to actually take them out they used pioneers with demo charges.

Not single 10 lb bags, either. They used approximately *a ton* of explosives on *each* concrete pillbox. They tried at first with a few hundred pounds, and ran out without destroying the thing (they damaged a few embrasures, but men inside were still tossing out grenades).

CM bunkers are remarkably ineffective against any sort of direct fire artillery weapon. The concrete ones are invunerable to any amount of indirect HE, and both types are essentially invunerable to any amount of small arms fire. These are obvious consequences of the use of the vehicle model, not anything to do with realism about bunkers.

[JasonC]

1000 rounds of 50 cal are 40 CM shots, the whole ammo load of a typical team. Nothing like 1 out of 10 would hit something as small as a bunker firing slit at range. If it did, you'd see a typical CM MG burst at men in the open hit 2-3 people, instead of about one chance in 7 of hitting one.

You must understand that a firing slit in a concrete pillbox is not just a vertical hole in a flat, thin wall like a house window. The side of a concrete bunker is 4 to 6 feet thick. So the firing slit is a "tunnel" that long.

The top of this tunnel is flat, horizontal. The bottom is not. It slopes upward as you go in. Over the length, it reduces the height of the slit by about half. That means a rise over run of perhaps 1 in 4 to 1 in 6, making a "glacis" significantly above horizontal.

When a round comes in, what happens to it depends on its vertical height. If it hits above the outer slit top, obviously it is stopped by the whole wall. Same below the slit. If it were light instead of an object, about half that get between would hit the glacis at some point. In fact it is somewhat more than that if the fire is from range, because the round is falling somewhat.

Hits on the glacis ricochet up. The whole set up is designed to throw those over the heads of the defenders. They might get a few concrete chips and dust sprayed at them, nothing more serious. Obviously if a very large caliber AP round hits the glacis, the men will be pinned by that, and 1-2 might be injured. But an MG bullet or small round is not going to do anything with such "secondary projectile".

The sides of the firing slit slant inward to achieve the same ricochet effect. So a round coming in not "straight on" will bounce off the side wall of the "tunnel".

A round that comes in just below the upper surface will make it through to the back of the "tunnel". But probably high compared to the men inside, straight on into the back wall of the bunker. Some small portion will pass between that and the glacis, and so have the right height to hit a defender if up and firing at that instant, and also along the right flight path side to side. In the case of a gun bunker, there is also the usual gun shield on the weapon, which helps especially with secondary fragments.

Overall, you are talking about 1-3 head sized targets, not the entire opening, to actually hit someone on the fly. This is true of rifle bullets, MG bullets, etc. And is the obvious reason bunkers are practically invunerable to small arms fire.

If you don't hit them on the fly, the bullet is just going to sail on to the back wall of the bunker. There it will make a pockmark and kick out flakes of concrete, burying itself in the wall. Or it might occasionally break in half or ricochet, but at low velocity.

Now, if the round is a 20mm instead, it has a burster in it. But that burster is on the order of 3 grams, a firecracker not a grenade's worth. And its going to go off either on striking the glacis, or on striking the back wall. With a tiny charge, that isn't going to do much of anything. If you do hit someone on the fly, you will incapacitate them certainly. You might damage the weapon if you hit it directly.

If it is only a wooden bunker, it won't have the same level of protection even against small arms fire. The opening in that case is typically kept to 6 inches height. It is typically through 2 layers of logs and one or more of sandbags, perhaps 2-3 feet all told.

I hope that clarifies somewhat.

[ April 10, 2003, 01:15 AM: Message edited by: JasonC ]

[John D Salt]

Originally posted by Hat Trick:

[snips]

Additionally, concrete bunkers are invulnerable to damage from artillery, as best I can tell. I did a test some time ago in CMBO, and found that even 14-inch battleship guns didn't affect them. Multiple direct hits, not even a "pinned" reaction. While I believe that most indirect fire would cause little damage to (well designed) concrete fortifications, I doubt that any above ground structure would be able to withstand this type of blast.

While it's a different theatre and a different kind of bunker (logs and coral concrete), PRO document WO 232/35, "Reduction of Japanese bunkers" mentions bunkers on Tarawa that withstood direct hits from 16-inch HE and 1,000-lb bombs. Clearly, some structures can withstand that kind of blast.

All the best,

John.

[Ace Pilot]

Originally posted by lcm1947:

I remember reading that it took like a 150MM cannon to take out a bunker and then it wasn't that it blew it up but caused the men inside to surrrender due to the shock, noise and terror. Can't remember the book but it was only a couple of months ago that I read it so remembered it.

Was it Citizen Soldier, by Stephen Ambrose? I just finished it and he described a group of infantry that had been assigned to take out several bunkers. They were discussing how to do it while minimizing casualties when a self-propelled 155mm howitzer rolled up. The commander asked if they needed help. They pointed to the bunkers. He opened the breach, lined up the barrel on the target, and fired a round. The infantry complained that the bunker was still standing. The commander replied that it didn't matter - anyone inside was dead or too messed up to put up a fight. The infantry found out he was right.

[Brigadier]

The "Sturm Tiger" is the ultimate "bunker buster"... 15.2" ordnance 2116 Blast effect! W00t!

It rocked my world