 Based on France's experience with trench warfare during World War I, the massive Maginot Line was built in the run-up to World War II, after the Locarno Conference gave rise to a fanciful and optimistic "Locarno spirit".French military experts extolled the Line as a work of genius that would deter German aggression, because it would slow an invasion force long enough for French forces to mobilise and counterattack.The Maginot Line was invulnerable to aerial bombings and tank fire and had underground railways as a backup; it also had state-of-the-art living conditions for garrisoned troops, supplying air conditioning and eating areas for their comfort.