The gros ouvrage fortress, the Ensemble de Bitche, is in the Alsace Lorraine, the ancient Franco-German bone of contention. It was here that France, between the wars, poured its national treasury and energy into this "Super-fortress." The German main defensive line, the Siegfried Line, was anchored by the captured French built Maginot, the Ensemble de Bitche.
The 44th, it's neighbor the 100th I.D. and the other attached units were tasked to capture and reduce this revolutionary advanced defensive system. Each fortress at Bitche was buried at an average of 118 feet under the Alsatian sandstone. Each fortress had a long central tunnel of stone and reinforced concrete with a “life zone” at one end and fighting zone at the other, all reached by secondary tunnels, stairways and elevators. Men, equipment and munitions were transported and served by trolley.
Each ouvrage at the Ensemble at Bitche lay within cannon reach of another one, allowing commanders to call on a neighbor to lay a barrage of antipersonnel fire directly on top of their fortifications if enemy troops appeared. This operation the French called “delousing.” The same cannon could "delouse" the other German defenses, in the vicinity of the fortress, in 1944.
The main entrance is reached through a retractable steel drawbridge over an antitank ditch, after which a seven-ton steel door set into the hillside gives onto nearly three miles of concrete passage-ways. During combat, the French staffed 812 men in 1940. Each worked three eight-hour shifts, “hot-bedding” or sharing sleeping quarters. The main entrance, a theoretical weak point despite the tank ditch and the seven-ton door, was protected by a 47-millimeter antitank gun. The 47mm gun was inter-changeable with machine guns via a an overhead rail. Many of the ouverage’s machine guns were mounted on cams that raised or lowered the barrels, as the guns swept the terrain around them. This automated killing machine consistently maintained a hail of bullets at about a foot above the ground. In 1944, instead of French, the Germans now defended the forts and used this deadly technology against the 71st Regiment led, combined arms teams.
Powered entirely by electricity and equipped with everything from wine-storage areas by the kitchen to a dentist's chair, jail cell and morgue, each Bitche gros ouvrage was a self-sufficient unit. Like a small underground city, each had its own wells, food supply and power generator, capable of up to three months of total autonomy. The World War I experience with gas attacks was parried by a ventilation-filtration system that created a slight overpressure within the fortifications.
The cannon crews fired blind, guided by ground-level observers telephoning to subterranean fire-control command posts. The cannon consisted of paired sets deadly accurate, French 75s. The pairs were housed in steel “pop-up turrets” set inside circular shafts of reinforced concrete. With nothing but the small arc of a rounded steel dome protruding aboveground, the weapon was practically invulnerable when lowered. To fire, the dome rose about two feet to expose the twin barrels within the rotating shaft.
Inside each cannon turret, a 360 degree image of the surrounding countryside was drawn along the circular wall, allowing artillery crews to visualize the targets corresponding to the numbered coordinates sent up to them by fire control. Included were calculations of every square meter within each cannon's range with an assigned coordinate.
All combat contingencies were considered in their design. Might an attacker infiltrate through the machine-gun fire and approach the outside walls, crawling where no one could see them? A little hand-operated launcher would deliver grenades out to the other side. If the enemy somehow get past the door into the passageway? Then they would be mowed down by machine guns in a bunker—a bunker within a fortress—set into the wall a few meters farther back. Should they pass the one of the forts bunkers? If worst came to worst, the passageway was mined so the push of a button could collapse the tunnel with a single explosion. Might they still come on, in spite of it all? Well, the men could evacuate through the secret emergency exit, a special little tunnel leading to a vertical escape shaft.
Source: Rudolph Chelminski "The Maginot Line"