Emael was the name of the most modern fortress
at the outset of World War II
It was constructed over 4 years beginning in 1931, at the junction of the Albert Canal and Meuse river. These two waterways were the biggest obstacles to any invasion force passing through the central part of the country from Germany. The strategic placement of the defenses at this spot were part of the centerpiece of the delaying tactics planned by the Belgian Army.
The German army knew they had to take the fortress quickly in order to overwhelm the defenders of the Flanders route into northern France, and that no conventional force could be assured of a victory in this assault.
Hitler came up with the crazy idea of crash landing gliders full of troops on the roof of Eben Emael to blow holes through the steel and concrete with shaped charges. A force of ten gliders was loaded with 78 combat engineers from the 7th Airborne Division and they took off on May 10, 1940.
The attack went almost exactly as planned, after crashing onto the top of the fort, the men leapt from the wreckage and planted their explosives on the roof of the building, attacking through the holes they created. The 78 German soldiers kept a garrison of over 1200 Belgian defenders entombed within the building for 24 hours, until the ground spearhead of the 4th Panzer Division reached them and put the defenses firmly into German hands.
The attack, as insane as it was, was one of the most successful and fruitful operations of the war, and probably did nothing to dissuade Hitler from enacting some of his other wacky plans later, to the detriment of his followers.