The Maginot Line largely did its job, and France fell anyway
France's great concrete barrier of the 1930s was nearly impossible to break: bomb-proof, tank-proof, air-conditioned, served by underground railways. Its purpose was to steer any German attack north through Belgium. In 1940 the Germans went north, as intended, but through the Ardennes forest just past where the heaviest works ended, and the plan unravelled.
Named after war minister Andre Maginot, the line ran along France's borders with Italy, Switzerland, Germany, Luxembourg and Belgium. Its logic came straight from the trenches of 1914 to 1918. France had about 39 million people against Germany's 70 million, so it wanted concrete to save soldiers, shield the industrial provinces of Alsace and Lorraine, and hold an attacker for the two to three weeks the army needed to mobilise. Ideally, the next war would then be fought on someone else's soil.
Calling it a line undersells it. The defended zone was 20 to 25 kilometres deep, beginning with border blockhouses often disguised as houses, then anti-tank posts about 5 km back, and a main belt starting roughly 10 km from the frontier behind six rows of upright steel rails. The biggest fortresses, the gros ouvrages, had at least six combat blocks joined by tunnels with small electric railways, and held crews of 500 to over 1,000. In total the system counted 142 ouvrages, 352 casemates and around 5,000 blockhouses, with supply depots about 50 km to the rear.
The weak point was political as much as military. The fortifications were never extended along the Belgian border, because Belgium feared being left outside the shield. Instead, under General Maurice Gamelin's Dyle plan, French and British troops would advance into Belgium to meet the Germans there. Gamelin judged the rugged Ardennes an unlikely route, or at least a slow one.
After the Mechelen incident of 10 January 1940 exposed German plans to the Allies, Germany adopted the Manstein plan instead, sending its armour through the Ardennes and across the Meuse before the Allies could react. The panzers then drove down the Somme valley, trapping the northern armies and forcing the Dunkirk evacuation. Ever since, the name has served as shorthand for an expensive safeguard that breeds false confidence.
Source: Maginot Line
