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World War II Armed Forces — Orders of Battle and Organizations Last Updated 02.10.2003

Belgian Fortifications, May 1940

Written by
Bernard Vanden Bloock

[ Overview | Deep Defences | Border Defences | Conclusions ]
[ Appendix A: Bunker Types | Appendix B: Weapons | Bibliography ]

Appendix A: Bunker Types

Belgian ‘Light’ Type Machine Gun Bunker


Help the infantry to conduct delaying actions. No prolonged or determined defence


Designed to sustain the impact of a single 77 mm HE shell or sustained fire from smaller calibre weapons

External dimensions

300x 320 cm

Wall thickness

40 - 60 cm (60 cm for walls exposed to enemy fire)

Roof thickness

50 cm


One heavy machine gun


One room, closed by a single steel door


The author drew up these plans from a half-buried bunker located in the Ourthe valley. All light machine gun bunkers had the same dimensions and wall thickness. Depending on the terrain, the door could be at the back of the bunker or on either side. Here it is on the side, at the bottom of a small staircase.

Belgian “Light” Type Machine Gun Bunker: Top View

Belgian “Light” Type Machine Gun Bunker: Top View.

Belgian “Light” Type Machine Gun Bunker: Front View

Belgian “Light” Type Machine Gun Bunker: Front View

Belgian “Light” Type Machine Gun Bunker: Side View

Belgian “Light” Type Machine Gun Bunker: Side View.

Belgian “Medium” Type Machine Gun Bunker

Medium machine gun bunkers were armed either with one or two heavy machine guns and their actual dimensions varied accordingly. Contrary to light bunkers, they were intended for prolonged fighting. They all shared the set of features listed below:


To be used as part of a battle line.


Designed to withstand sustained 150 mm HE fire and/or survive the impact of a single 220 mm shell.

External dimensions


Wall thickness

100 – 130 cm (130 cm for walls exposed to fire)

Roof thickness

115-130 cm


One to two heavy machine guns, grenade gullies for close defence


Lock-type entrance with two successive steel doors.

Plan of medium bunker

Simplified plan of a medium type bunker showing the common features of all medium bunkers : two doors (P1, P2), grenade gullies (LG), two firing ports (M), an entry defence port (P) and the emergency exit (R). The observations slits (Ob) are particular to the Dyle line bunkers

Medium MG Bunker - grenade gully

A cut view of the grenade gully system for close defence.

Medium MG Bunker - grenade gully exit

The exit of a grenade gully. The steel shutter that sealed off the exit is missing.

Medium MG Bunker - entrance

The entry lock of a medium bunker with a steel gate (P1) followed by a steel door (P2).

Medium MG Bunker - second door

This is what the second door looked like. The blinds were meant to improve ventilation, a steel shutter could be fixed on the inside to seal off the door completely if needed. This particular door is located not in a bunker but in one of the defence blocks of Fort Battice (PFL I).

“Medium” Type Machine gun Bunker: Single Machine Gun Type

The single machine gun bunkers all had the same external dimensions, i.e. 7 m x 4,60 m. The inner chamber or fighting compartment measured 270 cm by 200 cm. The entry lock was placed to the back of the bunker or to one of its sides, as the tactical situation required.

Medium Bunker - Single MG - plan

Medium Bunker – Single machine gun.

Bunker NV-16

Bunker NV-16, defending the approaches of Fort Aubin-Neufchâteau (PFL-I). The entry lock is on the right side.

“Medium” Type Machine Gun Bunker: Dual Machine Gun Type

There are many designs here as the position of the machine gun s relative to each other varied according to the local tactical requirements. In some instances, the guns fired in the same direction, in others they fired in opposite directions, and then there were many intermediate solutions. There is really no difference with the single machine gun bunker except in size and the presence of an emergency, crawl-through exit sealed by a removable barrier of steel girders and bricks hidden behind a cement covering. When the main exit was destroyed or blocked, the bunkers’ garrison were supposed to remove the girders, then use their rifle butts to knock down the brick and cement wall.

Another difference is that medium were designed to give lateral or flanking fire, never frontal fire. You will notice this when looking at the plans. The side of the bunker that is facing the enemy (i.e. the top side of the image) doesn’t have any firing ports, only a grenade exit.

Medium MG Bunker - Dual MG - plan

Simplified plan of a medium bunker with both machine guns firing in the same direction. This bunker is placed at the edge of a forest and fires into a clearing. The enemy is likely to come from the left of the picture. Note how the firing ports are protected from enemy fire by a large slab jutting out of the building.

Virtual Visit (Medium Bunker)

KW line Bunker

A typical KW line bunker. Coded LW10, this one defended a bridge on the Dyle North of Wavre, in the sector of the First British Division.

KW Line Bunker - field of fire

This is the field of fire of the firing port you saw on the preceding photograph. The Dyle runs somewhere to the right of the trees on your right.

KW Line Bunker - back

The back of the bunker. The emergency exit is hidden by the shrubbery.

KW Line Bunker - entrance

The author’s daughter, Valérie is standing in the entrance of the bunker. The wall she is ‘modeling’ is 130 cm thick. You can see one of the hinges of the entry gate.

KW Line Bunker - inside frame

Inside the frame of the steel door (P2). The gate (P1) is to our left. Note how it is defended by a rifle port on the opposite wall (P).

KW Line Bunker - first chamber

Valérie, inside the steel door’s frame, is now entering the first machine gun chamber. Emergency exit is to the left.

KW Line Bunker - grenade gully opening

A close up on the opening of the grenade gully.

KW Line Bunker - grenade insertion

Yours truly demonstrating how a grenade is inserted in the gully. This one would have exited at the back of the bunker, between the entrance and the emergency exit.

KW Line Bunker - first MG room

Standing just inside the second door, looking into the first machine gun room. You can make out the (sealed) firing port to the left.

KW Line Bunker - MG port

A close up view of the machine gun port #2. The rusted fixtures are what’s left of the “Chardome” gun mount.

Anti-Tank Bunkers

Anti-tank bunkers were either modified machine gun bunkers or large works specially designed to deal with a particular tactical situation. For the purpose of this article, we will call the former “small” and the latter “large”. Most anti-tank bunkers were concentrated in the PFL, but there were a few on the North-eastern border, in the Ardennes and along the Southern approaches to Brussels.

All bunkers were armed with one 47 mm anti-tank gun. In most instances, this was the Belgian C 47 D gun but some bunkers were fitted with the French APX2b tank turret. “Large” bunkers were armed with a 47 mm, one heavy machine gun, one searchlight and in some cases, an armoured observation cupola. “Small” anti-tank bunkers were armed with just the anti-tank gun. Both types sported some of the features of the medium Machine gun bunker (same wall and roof thickness, entry lock with two doors, grenade ports).

Large ATG Bunker - PFL

 “Casemate Mont”, a large anti-tank gun bunker of the PFL - I. It barred the road from Theux to Louveigné where it passed the small village of Mont.

Antitank Bunker - A23

Bunker A23 defending the Dutch border forward of the Bocholt–Lanaken canal. This large anti-tank gun bunker was located in Grevenbricht. The large firing port in the centre is where the 47 mm anti-tank gun was located.

Artillery Observation Bunkers

Artillery being an indirect fire weapon, its effectiveness is largely dependent on the presence of forward observers who can identify targets and direct the guns’ fire. Every Belgian artillery fort had a number of artillery observation posts attached to it. They were the “eyes” of the fort. Some of those posts were mobile; others were installed in bunkers. There was no standard design for artillery observation bunkers. Most were modified machine gun bunkers retro-fitted with an armoured observation cupola. Artillery observation bunkers will be described in more detail in the Forts article.

This article first appeared in World War II Online - Technical Publications.
Copyright 2005 Bernard Vanden Bloock
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