The Maginot Line, France, 1930-1940
What made the Maginot Line a mistake was simply that it was not long enough. French military planning during the 1920s and 1930s assumed that another war with Germany would be of long duration, and largely static, and the French assumed a defensive posture. They also assumed, rightly as it turned out, that the Germans would attack in the north through the Low Countries, as they had in 1914. Defensive preparations and plans of operation there were also part of the French defensive planning. Finally they assumed that an attack through the Ardennes would be slow, if one came at all, and they would have sufficient time to muster reinforcements to that area. Had they instead extended to Maginot Line to the north they would have precluded attack there.
The Maginot Line was virtually impervious to attack by artillery or aerial bombardment, and would have no doubt been successful in stopping any German attacks. Simply bypassing it left its garrisons out of the Battle of France, and allowed the Germans to flank the British and French troops to the north. When the British Expeditionary Forces arrived in France in 1939, the error of not lengthening the Maginot Line became apparent, and British and French engineers hurriedly extended the fortifications as much as possible, but they were unsuccessful in preparing adequate defenses. The Line was used by Allied troops resisting Germany’s Operation Nordwind in 1945, and proved to be an excellent defensive fortification.