Sorry, forgot to post this earlier. Mobile warfare is doctrinal, not technological. Technologically the French forces were even better equipped for mobile warfare than the Germans, but they never developed the doctrine to use it. The Germans called the doctrine Bewegungskrieg and had been using it tactically since the 1870s, but were unable to make it work strategically prior to WWII. The fort Eben-Emael was the one attacked by glider troops. It is Belgian, not French. The Maginot Line was never attacked using gliders or paratroops. The Schlieffen Plan was a right hook, a sweeping advance west through Belgium (and originally Holland) and across northern France then south toward Paris. The Battle of the Ardennes from the German perspective was more about pinning the French forces in place while their right wing swept south behind them to form a double envelopment. The WWII plan was a left hook through the Ardennes then northwest to the coast, avoiding Paris, to trap the Allied forces in Belgium. The plan was adopted because: 1. It was the only hope for victory, instead of a repeat of WWI. It was most definitely a desperation plan. 2. A copy of the original plan (similar to the Schlieffen Plan) fell into Allied hands on January 10, 1940. 3. Internal army politics that resulted in author, von Manstein, who made a personal appeal to Hitler when he was relieved of his position as Chief of Staff for Army Group A, and used the opportunity to present the plan. The original poster was interested if it was possible to create a very large fortification, nearly invulnerable to same generation weapons, to house a counterattack force in safety. The answer I think is a qualified ‘yes’ at this time, but by the time you finish building it (10 – 15 years) the weapons will have changed again, so the answer at the time of completion is, at best, probably not. That is the problem with large fortresses, they take so long to complete that they are already obsolete. But fortification is not dead in the slightest. The medieval castles and cement-brick-and-steel monsters of the Maginot Line are no longer relevant, but fortifications like Okinawa, Stalingrad, and the Kursk Salient in WWII are. Properly used fortification is a force multiplier that allows an inferior force to tie up a superior enemy force. If the Americans did not have control of the air then firebases would have been built differently, with larger garrisons, more artillery, extensive stores for a prolonged siege, and road and/or river access. Reality defines tactics.