Oh yeah, sure, blame it on the Belgians!

Fellow Belgian here, our ancestors had been naive...

Our main line of defense, the fort d'Ében-Émael, had been built by German workers. The German army had their plans, and knew the weak point of the fort: its vast, undefended roof (it was used as a football field by the soldiers).

During a dark night, they landed with gliders on the roof, and manually set up shaped charges[1] to destroy the turrets, which were resistant to conventional bombs.

Game over.

[1] http://en.wikipedia.org/wiki/Shaped_charge , damages seen from the outside: http://upload.wikimedia.org/wikipedia/commons/thumb/f/f6/Ebe...

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Edited to reconcile my foggy memory with the historic truth...

I'd be willing to bet some young combat engineer said "but what about the roof?" and some old general replied "you'll never get a horse up there!".

It's worse than that.

The roof should have been mined, but the soldiers petitioned the hierarchy to keep their sports field...