Les secrets de la ligne Maginot

Stretching from Belgium to the Alps, designed by an army of ingenious military engineers, the Maginot Line was a network of fortified bunkers connected by high-tech tunnels and defended by relentless artillery crossfire. It was meant to be an impenetrable obstacle. And yet... it failed. What role did it really play in France's WWII campaign? How did the Nazis finally pierce through?