Maginot Line at War 1939-1940

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Maginot Line

"The foundations of the Maginot Line were the war cemeteries of France." 
Vivian Rowe, The Great Wall Of France (Putnam: London, 1959)
Blocks 4 and 6 of Fortress Simserhof near Bitche in northern Alsace

Named after French Minister of Defense André Maginot, the Line was a series of permanent fortifications built to protect France’s borders with Germany and Italy.

Historians and writers differ over exactly what is meant by the name Maginot Line.  The term sometimes describes all of France's pre-WWII border defenses, or just the large, complex forts (termed ouvrages in French) actually facing Germany and Italy.  These different interpretations result from the way in which the Maginot Line evolved during its planning and construction, and the final form taken by the fortifications; which was considerably different from what was originally envisioned.  The view, that the Maginot Line includes all of France's border defenses, is the one adopted by authors of this website.

Planned in the 1920's and constructed in the 1930's, the Maginot Line was a direct result of France’s experience in World War I.  The broad purpose of the Line was to halt an invasion long enough for the French Army to fully mobilize, and then act as a base from which to conduct a counteroffensive.
For a contemporary French view of the geography where the Maginot Line was built, click on this link:

"The Military Consequences of the Return of the Saar to Germany" by Captain G. B. Guenther

Structure of the Line
The Maginot Line was a linear fortification, meaning that it was a series of forts built in an uninterrupted line.  The forts were spaced approximately 15 km apart; depending on the terrain.  Between the forts were interval casemates that supplemented the defenses of the forts.  The forts and interval casemates were joined together by anti-tank and barbed wire obstacles.  In sum, the forts, interval casemates, and obstacle belts formed the main fortification line (ligne of principal resistance) that was the backbone of the Line.  This line ran parallel to the border about 10 km inside of France.
Although the Maginot Line was a linear fortification system, the depth of the Line (i.e., from the border to the rear area) was between 20 and 25 kilometers wide.  A variety of other defensive structures – advanced posts, blocking positions along main roads, and shelters for local infantry reserves – broadened the Maginot Line into a fortification zone centered on the forts and interval casemates.
No two Maginot fortifications were exactly alike.  The various structures were adapted to the local terrain and combined as needed to form the defensive zone.  Major elements of the Line were:
1.  Forts (ouvrages).  The primary defensive feature of the Maginot Line was the ouvrage (literally “works,” in French), or fort.  There were two basic types – large fortresses (gros ouvrages) and small forts (petits ouvrage).1  Large fortresses were two to three times the size of small forts, and were also designated as artillery ouvrages because they were equipped with 75 and 135mm howitzers.  Small forts were designated as infantry ouvrages because they were only equipped with infantry weapons – machine guns, 37 or 47mm anti-tank cannons, and 81mm mortars.  Fortresses and forts typically had several combat blocks and entrances interconnected by a network of underground galleries.  The galleries and underground portions of the blocks contained the infrastructure needed to sustain the weapons systems and crew; such as command posts, power stations, ventilation systems, crew quarters, kitchens, ammunition magazines, and workshops.  A small fort’s crew was between 100 and 200 soldiers, while a large fortress was 500 to 1000 soldiers, or more. 

Fort (petit ouvrage) Bois-du-Four

Fortress Rochonvillers: munitions entrance block

Fortress Simserhof: main gallery with electric train

Fortress Simserhof: powerplant

Block 2 of Fortress Kobenbusch: infantry block

Fortress Simserhof: command post

Block 8 of Fortress Metrich: 75mm howitzer turret

Block 5 of Fortress Hackenberg: artillery casemate with three 75mm howitzers

Block 2 of Fortress Hackenberg: 75mm howitzer turret

Fortress Hackenberg: machine gun turret

Block 3 of Fort (petit ouvrage) Bovenberg

Click here for the Implementation Plan for Fortress Galgenberg

Click here for maps of Fortress Galgenberg

2.  Interval Casemates (casemates d’intervalles).  Casemates came in several different varieties, but were generally reinforced concrete structures with two stories or floors.  The lower level was below ground and contained the support infrastructure (power generators, ammunition stores, and crew quarters).  The upper level was at ground level.  It contained multiple firing chambers (rooms) armed with twin 7.5mm machine guns, and 37 or 47mm antitank cannons.  Casemates typically had one or more armored cupolas (cloches) for observation and self-defense.  The crew size was about 20 to 30 soldiers.

Interval Casemate Grand Lot

Casemate Koenigsmaker Sud

Interval Casemate Sinnerberg Est

3.  Observatories (observatoires) and Infantry Shelters (abris).  Observatories were specialized reinforced concrete casemates that contained optics and personnel to locate enemy forces and to direct the artillery fire of nearby fortresses.  Observatories were located on hilltops near the artillery fortresses.  Behind the main fortification line were reinforced concrete shelters for a company of infantry (200 to 250 soldiers).  Some shelters as served as command posts for the interval infantry.

Abri (Infantry Shelter) d'Ising

4.  Obstacle Belts.  Forts and interval casemates were connected by anti-tank obstacles and barbed wire entanglements.  The anti-tank obstacles were either rows of rails (up to six rows deep) set vertically in the ground, or wide earthen ditches.  Anti-tank barriers also blocked all roads through the fortification zone.  Accompanying the anti-tank obstacles was a belt of dense barbed-wire entanglements.  Together, these obstacles extended across the front of the main fortification line, interrupted only by impassable terrain.

Anti-tank obstacle belt

Antitank obstacle near Fortress Shiesseck

Anti-tank ditch in Sarre region

Barbed wire obstacles

Anti-tank barriers for blocking a road near Maubeuge

5.  Field Fortifications.  After construction of the primary Maginot fortifications was complete and the French Army occupied the Line, engineer and troop units built concrete blockhouses to supplement the main fortification line.2  These field fortifications came in a wide variety of designs and quality.  In regions where no forts or interval casemates were built, the field fortifications were the primary defensive structures, and in general, were only suited for local defense.

Blockhouse near Lille

Blockhouse in the Sarre region

For a description and recent photos of the Line's various elements see the Wikipedia entry for the Maginot Line at
Maginot Line by the Numbers3
Fortresses (gros ouvrages)    22
Forts (petits ouvrage)            36
Casemates                         311
Infantry Shelters                   78
Observatories                       14
Blockhouses         approx. 4000
Construction of the Line 
The main period of construction took place from 1930 to 1936 when the primary fortifications were built.  Thereafter, the Line was constantly improved up until the German attack in May 1940.  Due to funding difficulties, some forts were scaled back in size and weaponry while many casemates and other structures remained incomplete; missing weapons and cupolas.  As a result, the forts and casemates available for combat in 1940 were less in number and capability from those envisaged in the original plan.
The Maginot Line in north and northeast France was built in three distinct phases of construction:
1.  1930-1936.  Construction of the fortifications in the two areas most threatened by German invasion.  These became two fortified regions (régions fortifiées) – Metz and Lauter – also called either the Maginot Line Proper or the Old Fronts (anciens fronts).  RF Metz protected the industrial and mining areas around Metz and the main railroads of Lorraine.  RF Lauter protected northern Alsace from the Sarre area to the Rhine River.  These sections of the Maginot line were the strongest built.
2.  1936-1939  After the German re-occupation of the Rhineland, RF Metz was extended west to Montmedy and RF Lauter was extended west to the Sarre region.  These parts of the Line became known as the Maginot Line Extension or New Fronts (nouveaux fronts).  Fortifications were also constructed to fill the Sarre Gap between RF Metz and Lauter and in the Lille-Maubeuge area along the primary invasion route from Belgium.  Finally, the casemates of the Rhine defenses were built. 
3. 1939-1940 Once the French Army occupied the Maginot Line, the troop units constructed field fortifications all along the border reinforce the Maginot forts and fill gaps in the Line.
Employment in Battle
The Maginot fortifications not intended to fight in isolation. Not only were the forts and casemates weapons mutually supporting, but the main fortification line was integrated with reinforcing interval troops and artillery.  In theory, an attacking German force would have to fight the Maginot Line as an integrated system, not as individual forts and casemates.  In reality, as the campaign in the West unfolded and the German Army advanced into France, the French High Command ordered the withdrawal of interval troops and artillery for employment elsewhere.  This decision stripped the Line of important firepower and infantry reserves.  Thus, when the Germans attacked, they did not fight the Line as envisaged by its designers.  The withdrawal of the interval forces is an important consideration to any study of the Maginot Line’s combat performance.


1.  The authors of this website use the term “fortress” for gros ouvrage and “fort” for petits ouvrage.

2.  “Blockhouse” is used to mean above ground concrete fortifications and “bunker” for underground fortifications.

3.  Source of information is L'Association des Amis de la Ligne Maginot d'Alsace (AALMA)   (