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"Pill boxes internal walls - how effective were they?" Topic

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25 May 2021 12:42 p.m. PST
by Editor in Chief Bill

  • Changed title from "Pill boxes internal walls hoe effective were they" to "Pill boxes internal walls - how effective were they?"

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UshCha25 May 2021 8:25 a.m. PST

Here is a pill box from WW2 the design probably has not changed that much in the cheap and cheerful range.


Many have internal walls such as this one. Are they really a survival thing or could guys on the far side of them really function if there was much coming into the opposite side (say a remote Grenade blast or some 0.303 rounds from an MMG?.

Alternatively are they just an aid to getting out quick if it all goes wrong.

Perhaps as an aside how do you deal with this issue in a game assuming you take your games as a serious study. Clearly over simple rules can't cope with reality so their solutions are of zero interest.

Personal logo ColCampbell Supporting Member of TMP25 May 2021 9:03 a.m. PST

They are called "inner blast walls" for a reason. They prevent direct fire coming through the firing slits or rear door from going clear across the interior, as well as blocking the blast/shrapnel effects. I doubt if .303"/7.62mm machinegun rounds would penetrate those interior walls.

Whether anyone on the opposite side would be immediately combat effective after a grenade or shell exploded on the far side is something I can't directly answer. But I would presume there would be some degradation in the defenders' effectiveness for a short while afterwards.

As far as handling this type of design in a wargame, you would just about have to do a 1:1 skirmish type game with each portion counting as a separate room.

Hope this helps some.


Shagnasty Supporting Member of TMP25 May 2021 9:43 a.m. PST

I was able to exam one of these on the grounds of Bodiam Castle some years ago. Looked simple but effective.

Personal logo David Manley Supporting Member of TMP25 May 2021 10:00 a.m. PST

I was inadvertently on the other side of something less substantial when an 82mm mortar round went off (don't ask) and I was fine, so I would expect them to be quite effective against the design threat. AFAIK they were well tested prior to use.

robert piepenbrink Supporting Member of TMP25 May 2021 11:31 a.m. PST

I'm sure internal dividers are of some use--but I note that the standard Albanian PZ Bunkers--dome-shaped, but about the same area as those Type 24's--didn't (don't) have them, and no one does bunkers like Albania did. Some use, but not cost-effective would be my guess. Not that any miniatures gamer cares about efficient use of resources.

Personal logo Zeelow Supporting Member of TMP25 May 2021 7:56 p.m. PST

Nothing to due with the question, but in the 3rd grade (1953) I used to play army with some buddies in a couple of German machine gun bunkers located near a railway station in Bavaria. I'd never seen concrete walls so thick! So much for memories of long ago.

Zephyr125 May 2021 8:11 p.m. PST

Pillbox designs are going to be as varied as the terrain they are built into (i.e. adaptable) Good examples of this are Japanese fortifications on the islands they defended. And, pillboxes aren't meant to be a standalone feature; They need to be mutually supporting, with interlocking fields of fire, etc. So yes, a simple solution isn't going to be an effective "simulation" for you…

UshCha26 May 2021 8:23 a.m. PST

Zephyr1, its taken as read that the system should interlock with other troop types some of which will not be in bunkers. But in the end the enemy either fails or starts to unpick the defense. Then the limitations of the bunker become a significant factor potentially. Without being able to set up credible defenses to me there is no point in playing a defensive game.

Martin Rapier26 May 2021 10:05 a.m. PST

The drill for taking out pillboxes (see e.g. Infantry Fieldcraft and Training) was to get in close under supporting fires and smoke then post grenades through the slits – which implies that close up the internal walls didn't help much against an enemy infantry section at close range. I am sure they worked fine in reducing the lethality of weapons fired from longer ranges.

AP or HE fired into the embrasures from close-ish ranges also worked as well, and obviously if you have armoured engineer assault vehicles like AVREs, it is game over once the big guns get close, let alone armoured flamethrowers. Direct fire bunker busting artillery (122mm, 155mm, 88s) would also blow them apart quite handily.

Wolfhag26 May 2021 3:49 p.m. PST

Some pillboxes and bunkers were composed of multiple internal sections that allowed the occupants to move from one section to another. You'd have to collapse all of the sections to knock it out. There could also be an underground entry/exit that would allow the defenders to re-occupy it if it was not destroyed by demo charges or a bulldozer. The Japanese used these types.

In the early 1970s the drill was Blind, Burn, and Blast. Blind with suppressive fire and smoke/WP allowing the assault team (flamethrower and demo charge) to get close enough for the flamethrower (Burn) to really suppress the defenders (flamethrowers rarely took out a bunker) allowing the engineer to place the demo charge (Blast). Sometimes it took multiple charges.


Thresher0126 May 2021 4:34 p.m. PST

After the D-Day landings in Normandy, the USA used 155mm guns on the M40 Gun Motor Carriage to reduce, and/or eliminate German bunkers.

UshCha27 May 2021 1:00 a.m. PST

Martin thanks for that. Wolfhag, I build a fold flat "semi-scale" i.e expeident shape but about the right size for 1/72 and even a single compartment one is big, 42" walls (as in the typer 24)does not help. One of the reasons I personall prefer 1/144 scale.

UshCha28 May 2021 12:23 a.m. PST

I thought about Martins post. Obviously in some ways its correct. However one of the key issues with fixed defence is that it can be interlocked and will if the defencder has any sence have fixed line fire lines so can still fuction close in even if Blind to some extent.. Plus troops near ( 20 yds maybe) may be able to protect it even if wreathed in smoke. That to me is the fun of trying to unpick a good defence, or set one up.

Puster Sponsoring Member of TMP29 May 2021 2:30 a.m. PST

I would assume that "grenades through the slits" is exactly one of the situations where internal walls help. Without there certainly is not much to do for those inside. If you happen to sit on the right side of the wall you may fight on.
It probably was worth it.

somehow doubt that the "Albanians not doing it" is a valid measure for their effectiveness, rather a sign of actual cost of concrete vs. potential cost of lives for the Albanian government. As it came out, the tradeoff was correct for them, they never had to use them.

Wolfhag29 May 2021 7:19 p.m. PST

In a well-built and designer defensive structure frag grenades through a slit will probably wind up exploding mostly harmlessly in a grenade sump. WP and Thermite grenades would be different. Even two-man fighting holes were supposed to have a grenade sump but I've never seen it used in a game.

I've been collecting fortification diagrams for the same reason.


UshCha31 May 2021 3:12 a.m. PST

I had a thought about grenade sumps. Many years ago I was an Acoustics engineer. A grenade sump like body armour would keep you alive, however keeping you functioning is another story. The noise alone of a grenade going off in the sump, typicaly they are not very remotes and the surfaces of a pill box are normally good reflectors would of itself be in the painful range. Now you would still be alive as there would be no fragments to speak of but pain and smoke would be definitely suppressive for a bit. A few and it would probably be intolerable and time to leave. Now that is probably too much detail for my sort of game. So it does not surprise me that grenade sumps are not a feature of a game directly but absence of them in limited circumstances could make a structure more vulnerable.

Now in a few scenarios we have distinguished between the standard open slit and those more sophisticated points that either use tank turrets (classed as static tanks) and some structures that have some form of sliding shutter to reduce incoming fire when closed but require opening to fire.

It does seem to me that defenses are a much undervalued in terms of interest historically and in game terms.

Wolfhag03 Jun 2021 6:52 a.m. PST

In a game, a frag grenade going into a grenade sump could give the results as an offensive grenade (blast/suppression only, no fragments of causalities). That could allow the attackers to get on top of the structure or in a blind spot to place a demo charge or use a flame thrower.

US WWII Pineapple grenades had 2oz of explosive, the M67 has 6oz. Many of us experienced 1/4 pound blocks (4oz) of C4 going off in a demo pit within 3 feet with no adverse results. During a training op I got too close to a taped-off demo area (right next to the tape, I thought the exercise was over) and the wise guy Engineer blew three blocks of C4 within 5 feet of me. I got knocked down but got right back up and kept running with no ill effects.

I did have a WP grenade go off within about 15 feet of me. It makes a loud "pop" sound, no concussion. However, the pyrotechnics display was awesome.

As you said, in a confined area the blast would be worse. If that happened you'd probably want to surrender, shift, relocate or fall back but that is not always an option when the enemy is 20 yards away.

My son told me during room clearing they threw two M67 frags into a room and immediately entered. The first guy in the stick was hit as soon as he entered. I'm not sure what they were hiding behind.

It does seem to me that defenses are a much undervalued in terms of interest historically and in game terms.

I agree. A lot of detail needs to go into the # firing positions/loop holes, fields of fire, and blind spots. From what I've read, pillboxes and bunkers were normally taken by 1-3 guys in an assault team using grenades, flamethrowers and demo charges. It's not normally a charge with a whole squad or platoon. They also had mutually supporting positions too.

The Battle of Tarawa gives a good description of taking out coconut bunkers. It took 20-25 rounds of HE from a Sherman 75 concentrated in one spot to breach it. There is also a good WWII training video showing the effects of direct fire guns of 37 and 75mm against concrete structures.


bobm195903 Jun 2021 7:50 a.m. PST

As well as any benefits to occupants from things coming in from the front the internal walls will also make the roof considerably stronger (assuming they are full height)

Blutarski03 Jun 2021 5:34 p.m. PST

In the later part of the war, the Japanese moved their defensive systems away from the beaches to the interiors of the islands, where underground bunker complexes dug into very difficult creviced volcanic terrain. Air strikes and artillery were unable to effectively reach them and tank access varied from impossible to difficult due to the highly broken nature of the ground on the island interiors. This phenomenon was most notably encountered on Peleliu, Iwo Jima and Okinawa.

The more I read about these late war Japanese defensive works in the PTO, the more surprised I was by the complexity and imagination employed. By the time of Okinawa, the Japanese were building great underground bunker complexes featuring numerous cunningly camouflaged firing positions plus sleeping quarters, mess and first aid stations and supply storage, all inter-connected by artillery-proof underground tunnels. The nightmare experience of the Maries' efforts to capture the "Sugar Loaf" on Okinawa is a good example IIRC, it required sixteen separate formal battalion-level assaults before the "Sugar Loaf" (a very modest and unremarkable ridge position) was finally cleared. Dealing with these sorts of complexes was in many respects more akin to siege opersations than tactical combat.

An entire set of wargame rules could be written, concentrating just upon the various tactics devised to deal with these types of fortifications bulldozers burying firing ports and exits; assault parties pouring dozens of gallons of gasoline down ventilation pipes, then igniting it.

Serious and bloody "no holds barred" business.


Wolfhag04 Jun 2021 6:52 a.m. PST

Japanese pillboxes and bunkers that housed larger guns normally had a steel door they could close when under assault or being fired on. The coconut log bunkers were especially resilient because the spongy wood absorbed a lot of the concussion. After Tarawa, it was estimated they needed a direct hit from a 2000lb bomb to destroy them.

The large blockhouse on Red Beach 2 at Tarawa repulsed two days of assaults by 2/8. Finally, an 81mm mortar round went through an opening in the roof for an MG and exploded ammo inside. This allowed a close assault by Lt Bonneyman with a flamethrower and TNT charges. Survivors of the assault ended up utilizing two 54-pound blocks of TNT and an entire case of gelatin dynamite on this blockhouse alone, with engineers applying each of these charges by hand, literally hugging the deadly fortification in the process.

When the Japs tried to escape through the rear doors there was a Sherman tank waiting that mowed them down with multiple canister rounds.

Some ad hoc techniques were to tape a grenade to a block of C4 or a mortar round and toss it through an opening as grenades themselves had limited effectiveness and make a grenade sump useless. Even with multiple sections in a bunker a flamethrower could suck all of the air out and suffocate the occupants. Thermite and WP grenades would force the occupants to evacuate too. A Bangalore torpedo through an opening got the job done too.


UshCha11 Jun 2021 12:06 a.m. PST

So has anybody got a real world layout of a pillbox defence and how the wire and trench system lines up/positiong gaps in the wire. I really have not found a good general explanation and guide to system desigh.

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