At dawn on 10 May 1940, 10 large transport gliders carrying an elite unit of German paratroopers (codename GRANIT) landed on the roof of the fortress.
There was no official declaration of war.
Shortly after landing, an attack group disarmed the air defence machine guns. Most of the observation cupolas, machine gun bunkers, artillery bunkers and artillery cupolas were neutralised very quickly through the use of a new type of explosive, the hollow charge.
Gliders also landed on three bridges over the Albert canal to the north of the fortress and two major bridges were captured.
Counter-attacks by the Belgian artillery in the fortress failed because of a lack of automatic weapons and training The adverse terrain and regular bombardments by the German Luftwaffe ensured that the German attackers kept the upper hand.
Artillery fire from Fort Pontisse and Fort Barchon in Liège was useless as the German soldiers found cover in the bunkers they had already overcome.
During the night of 10 to 11 May 1940, German ground forces crossed the Albert canal and the fortress was surrounded.
By shortly before midday on 11 May 1940, just two artillery bunkers were still operational and defensive fire was impossible because the observation posts had been neutralised. The defending forces’ situation had become critical. The destructive effect of the new German explosives had destroyed the morale of the garrison. Many soldiers in the garrison were either dead, seriously wounded or demoralised. The defenders called a cease fire and around noon on Saturday 11 May 1940, the fortress surrendered. The fort had been taken by the enemy.
The hollow charge
The hollow charge bomb, weighting 12.5 or 50 kg, is filled with explosives, but unlike traditional bombs, the power of the explosive is focused in the hollow section in the middle of the bomb.
As the explosion is concentrated on a single point, a 50 kg hollow charge can penetrate 20 to 25 cm of steel and 35 cm of concrete. A vast quantity of concentrated gas is released during the explosion and, with a heat wave of around 2800° Celsius, this creates a pressure wave that destroys and burns all the material underneath.
The functional principle had been described as early as the late 18th century, but it was not translated into a usable weapon until the late 1930s. (Munroe effect, 1888. First use in 1792).
The attack on Fort Eben-Emael was the first time this new weapon had been used.
The psychological effect of the attack
The German attack succeeded on various levels.
Not only did it break through the positions on the Albert canal but it was a psychological blow to the Belgians and the Allies and a huge boost for the Germans: the strongest fortress in Europe had been taken in the minimum of time!
The breakthrough also had a wider strategic effect.
As planned by German military command, French and British troops withdrew into the Belgian interior, clearing the way for the German attack through the Ardennes.
The result is well-known: allied troops were surrounded in Belgium and pushed back to Dunkirk and Calais.