How the Nazis Managed to Capture the World’s Strongest Fortress in Under 20 Minutes

In the early morning hours of May 10, 1940, soldiers manning the Belgian fortress of Eben Emael looked up at the sky and beheld an alarming sight: nine strange slender-winged aircraft descending silently towards them. Within seconds the aircraft skidded to a halt and disgorged 54 highly-trained German airborne troops onto the fort’s grass roof. Little could the garrison have imagined that in less than half an hour their fortress – the most modern and impregnable in the world – would be brought to its knees in one of the most daring and successful assaults of the Second World War.

To understand the importance of Fortress Eben Emael, we must first go back to the start of the First World War. The German Schlieffen Plan called for the German Army to outflank the French by passing through neutral Belgium. Though Belgium had extensive fortifications protecting strategically vital city of Liege, these were quickly pounded to rubble by heavy German siege guns, and the German Army marched right through. Eager to avoid a repeat of 1914, after the War the nations bordering Germany built elaborate border fortifications, the most famous of which was the French Maginot Line. Between 1932 and 1935 Belgium spent over 24 million Francs modernizing the Liege fortifications, making greater use of reinforced concrete and spacing the forts further apart to protect them from artillery. And the centrepiece of these modernization efforts was Fortress Eben Emael.

Fortress Eben Emael sits on a diamond-shaped embankment around 1000 meters long and 900 meters wide, bordered to the East and West by the Albert Canal and Geer River and to the South by a 10-meter-deep antitank ditch. Atop the fort sit 6 reinforced-concrete artillery casemates: Maastricht 1 and 2 in the North and Visé 1 and 2 in the South, armed with 75mm guns, and Canal 1 and 2 along the banks of the Albert Canal armed with 60mm antitank guns. These were supplemented by three massive retractable rotating turrets or ‘cupolas’: Cupole 1 and 2 armed with 75mm guns, and Cupole 120 armed with 120mm guns. Rounding out the Fort’s defences were three more blockhouses: Mi-1 and Mi-2 armed with machine guns, and Block 1 at the entrance to the Fort armed with a machine gun, antitank gun, and a searchlight. These strong points were connected by 4.5 km of underground tunnels built on two levels: an intermediate level for moving men and ammunition, and a lower level housing the barracks, kitchen, infirmary, and ammunition magazines. Garrisoned by around 500 men, with another 500 kept in reserve in the nearby village of Wonck, the Fort was positioned to protect the vital bridge crossings over the Albert Canal, and its batteries were integrated with those of neighbouring forts, allowing them to provide mutual fire support in case of enemy attack.

Given these formidable defences, it is easy to see why Fortress Eben Emael was considered virtually impregnable, and why it weighed so heavily on the minds of the German High Command in the late 1930s. As with the Schlieffen Plan of 1914, Fall Gelb – or “Case Yellow” – Hitler’s plan for invading Western Europe in 1940, called for the German Army to outflank the Maginot Line by driving through Belgium and the lightly-defended Ardennes forest. But before this could happen the Army first had to cross the Albert Canal, which meant that Fortress Eben Emael and its heavy guns would have to be silenced. But the more German planners examined the Belgian defences, the more impossible the task appeared. Fall Gelb seemed doomed to fail. Incredibly, the radical solution to the problem came all the way from the top: from Adolf Hitler himself. If Eben Emael couldn’t be taken from the ground, Hitler thought, then how about from the air?

Though the tactic had first been demonstrated by the Soviet Union in 1934, the Germans were the first to make effective use of paratroops – or Fallschirmjager – forming the world’s first dedicated airborne unit, the 7th Flieger Division, in 1936 under the command of Generaloberst Kurt Student. On April 9, 1940, the Fallschirmjager carried out the world’s first airborne combat operations as part of the German invasion of Denmark and Norway, seizing key airfields and bridges at Masnedo, Alborg, and Oslo.

On October 27, 1939, Hitler summoned General Student to the Reich Chancellery and asked if it would be possible to take Fortress Eben Emael by dropping paratroopers onto its roof. At first Student was skeptical; parachute technology at the time did not allow for precision landings, and required the Fallschirmjager’s weapons and equipment to be dropped separately in containers. By the time the scattered paratroops had regrouped and collected their equipment, they would have lost the vital element of surprise. And even if the attackers could be landed quickly in a small area, what could a handful of lightly-armed paratroopers hope to accomplish against a fortress designed to withstand even the most powerful artillery? But as Student continued to ponder Hitler’s question, he realized that Germany possessed two secret weapons that just might make this audacious plan feasible after all.

The first of these weapons was the assault glider. The Versailles Treaty imposed upon Germany in 1919 forbade it from possessing an air force, so  in order to continue training pilots the German government embraced the sport of sailplane gliding, establishing hundreds of gliding schools and clubs around the country. Pilots trained in these establishments would form the nucleus of the new German Air Force, or Luftwaffe, when the Nazis came to power in 1933. In 1936, the German Research Institute for Sailplane Flight, or DFS, developed the DFS 230, the world’s first combat glider. Towed into the air by a Junkers Ju-52 transport aircraft, the DFS-230 could glide silently for up to 12 miles and deliver 10 fully-armed paratroops directly onto their target with pinpoint accuracy.

The second secret weapon in the German arsenal was the hollow or shaped charge. This consisted of a 50kg explosive charge with a conical cavity lined with copper. When detonated, the explosive shaped the copper cone into a high-speed jet of molten metal that could punch through 25 inches of steel or concrete. Together with flamethrowers for taking out bunkers, the combination of glider-borne troops and hollow charges was the perfect recipe for defeating the world’s mightiest fortress. Within days of his meeting with Hitler, Student assembled a crack team of 480 Fallschirmjager designated Sturmabteilung Koch – after their commander, Lieutenant-Colonel Walter Koch – and began intensive preparations for the assault on the fortress.

The plan relied on close coordination and split-second timing. The men of Sturmabteilung Koch would be divided into four groups, code-named Steel, Concrete, Iron, and Granite. Steel, Concrete, and Iron would land first, capturing the canal bridges at Veltzeldt, Froenhoffen, and Canne and preventing the defenders from blowing them up. Then, the men of Granite would land atop the fortress itself and take out the blockhouses and cupolas so their guns could not be brought to bear on the occupied bridges. All four groups were then dig in and hold their objectives until relieved by German ground forces.

Training began in November 1939, with Czech border fortifications standing in for the blockhouses of Eben Emael. Such was the need for absolute secrecy that the paratroops were not even told what their target was, and trained in plain uniforms without insignia. They were not even allowed to handle the top-secret hollow charges, practicing instead with concrete blocks fitted with handles. Meanwhile, the glider pilots practiced precision landing, and here they ran into a major problem: the gliders took too long to skid to a halt, greatly increasing the risk of a collision on the tiny fort roof. After a number of experiments, it was determined that wrapping barbed wire around the landing skid adequately shortened the landing distance. By early 1940 the training was complete, and the paratroops were moved to airfields close to the Belgian border where they awaited the signal to attack.

That signal came in the early hours of May 10, 1940. At 3:30 AM the men of  Sturmabteilung Koch rose, donned their equipment, and climbed into their gliders. Less than an hour later the Ju-52 towing aircraft roared down the runway and up into the morning twilight. As radio signals might have warned the enemy of the attack, the transports were guided to their release points by a line of flares laid out on the ground below. But almost immediately, problems began to dog the mission. Due to a misunderstood signal, one glider was cast off too early, forcing it to make an emergency landing near Duren in Germany. At the same time, the glider carrying Lieutenant Rudolf Witzig – commander of Group Granite – broke its tow-line and was also forced to land near Cologne. This left Group Granite with only 9 out of 11 gliders – and 54 out of 85 men – with which to carry out its attack.  Problems continued as several gliders strayed too far over the Dutch border and were fired upon by antiaircraft guns. One glider had its control cables shot away, causing it to plunge 12 metres into the ground, injuring its pilot and several passengers.

Nevertheless, at 5:20 AM Groups Steel, Concrete, and Iron landed at their respective bridges. The defenders at Veltzeldt and Froenhoffen were taken completely by surprise and quickly overtaken, with the Froenhoffen bridge barely being saved from destruction by one Corporal Stenzl, who stormed into the bridge bunker and tore out the firing cables with his bare hands. Over at the Canne Bridge, however, Group Iron was not so lucky. The moment the Belgian defenders spotted the gliders descending, they immediately blew up the bridge.

Only minutes later, the 9 remaining gliders of Group Granite descended upon the grassy roof of Fort Eben Emael. One member of the Garrison, Private Antoine, later described the scene:

“As the morning began to dawn, we heard gliding noises in the air but no engine noise. We immediately gave the alarm to the Senior Staff inside the Fort, then without waiting for instructions from the inside, our Senior Sargent gave the order to open fire. Flares sprayed from the 5 guns, but that was wasted effort. Several gliders actually came rushing down on us, and we were surrounded. One of them hit our machine gun with a glancing blow as it approached and knocked it over.”

It is impossible to describe what happened next in chronological order, as the attack took place simultaneously across the Fortress. But it is possible to give a taste of the chaos that unfolded over the next several minutes.

Among the first structures to be attacked were the Maastricht 1 and 2 blockhouses. After blowing through the observation cupolas atop the blockhouses with shaped-charge mines, killing the gun crews inside, the paras placed another mine below the guns, blowing them off their mounts and opening a hole large enough to crawl through. The paras then entered the blockhouses and dropped grenades down the entry shafts, destroying the staircases and ammunition elevators. Meanwhile, other groups were busy trying to disable the massive gun cupolas. The armour of Cupole 120 proved too thick for the mines to penetrate, but by a twist of fate the guns and ammunition elevators malfunctioned and the turret was unable to fire. However, a rather unusual problem soon cropped up. A certain Private Schmidt had replaced the water in his canteen with schnapps, and was now sitting drunkenly atop the still-rotating turret, forcing his comrades to pull him down before stuffing the gun barrels with explosives and disabling them for good. Cupole Nord and Sud also proved impossible to penetrate, but the paras managed to disable them by jamming the mechanism with a shaped charge and dropping grenades down a periscope hole.

Across the Fortress, other extraordinary events were taking place.  Upon landing, Heiner Lange, the glider pilot who had knocked out the machine gun at the Mi-Nord blockhouse with his wing, rose from his cockpit brandishing a pistol and a knife. The sight of him so frightened the defenders that 16 of them immediately surrendered. The commander of Lange’s assault group, Helmut Wenzel, then proceeded to blow a hole in the blockhouse and climb inside. There in the smoky darkness, he heard a telephone ringing and picked it up. Hearing a voice frantically speaking on the other end, he announced in perfect French, “The Germans are Here.” A moment later, he heard the other man exclaim: “Mon Dieu!” – My God!

And the Belgians had good reason to despair. Barely 20 minutes after landing, the men of Group Granite had successfully knocked out nearly every gun emplacement and entombed the garrison deep within the fort. At 5:42 AM, a signal was sent out by radio: “Objective achieved. Everything in order.”

Deep inside the fortress, the mood of the garrison could only be described as grim. Not only had they been taken completely by surprise, but their defence had been severely hampered by a series of poor command decisions – including that to garrison the fortress only with artillery troops. As it was thought impossible for infantry to penetrate the outer defences of the fort, little effort was spent on defensive infantry training. Even more alarming, Mi-Sud, one of two machine-gun blockhouses intended to defend against infantry assault, as actually empty during the attack itself, its crew tied up dismantling a temporary command shed by the entrance as per regulations. The three gun cupolas were also not provided with anti-personnel canister shot, and the guns themselves could only be fired on the orders of the surrounding infantry divisions. Adding to the garrison’s misery, the blast from a German explosive charge had caused barrels of Calcium Chloride used to clean the latrines to burst, filling the tunnels with Chlorine gas and forcing the men to don their gas masks.

Nonetheless, the commander of the Fort, Major Jottrand, ordered a counter-attack, and over the next six hours the men of Group Granite were tied down preventing a breakout by the garrison, sustaining many casualties in the process. Then, at noon, a single DF-230 glider descended onto the fort, and from it climbed none other than Lieutenant Witzig. Upon landing near Cologne, Witzig had flagged down a passing railroad official, commandeered his bicycle, and ridden to a nearby town where he phoned Luftwaffe high command and ordered a new Ju-52 to tow him back to the fort. Upon landing, Witzig immediately took command and rallied his men, pressing home the attack on the garrison and finally sealing them inside the fortress. But at that moment surrounding Belgian forts began opening fire on Eben Emael, raining over 400 shells down on the paras in an effort to dislodge them.

But the writing was already on the wall for Belgium. That evening the 51st Armoured Engineer Battalion of the German 6th Army reached the banks of the Albert Canal and prepared to make the crossing. Before this could happen, however, the antitank guns of the Canal Nord and Canal Sud blockhouses had to be silenced. So under the cover of darkness, Lieutenant Witzig and his men made their way to the top of the embankment and lowered explosive charges on ropes onto the gun emplacements, destroying them and allowing the 51st to cross the next morning. Then, at noon on the 11th of May 1940, only 30 hours after the assault had begun, the garrison of Fortress Eben Emael finally surrendered. Only 42 days later, the French Government capitulated, making Hitler the master of Western Europe.

The assault on Fortress Eben Emael was one of the most extraordinary tactical coups of the Second World War, and the ultimate demonstration of the German concept of Blitzkrieg or “Lightning War.” For their efforts every man involved in the operation was personally awarded the Iron Cross or the Knight’s cross by Hitler himself – all, that is, except for Private Schmidt with his canteen of schnapps.

But it would also be the beginning of the end, for never again would the vaunted Fallschirmjager enjoy such success as purely airborne force. On May 20, 1941, the Nazis launched Operation Mercury, the airborne invasion of the island of Crete, which though ultimately successful inflicted such high casualties among the airborne troops that thereafter they were forbidden from participating in large-scale operations. For the rest of the war the Fallschirmjager would largely be used as elite ground troops, serving with distinction in such actions as the Battle of Monte Cassino. It would also be one of the last times Hitler’s intuition would serve him well, with a series of increasingly poor decisions pushing Germany further towards disaster and ultimate defeat.

But if nothing else, the assault on Fortress Eben Emael dramatically showed how even the strongest fortifications, when based on outdated conceptions of warfare, are no match for modern tactics, confirming the old adage: Generals always fight the last war.

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Expand for References

Gukeisen, Thomas, The Fall of Fort Eben Emael: The Effects of Emerging Technologies on the Successful Completion of Military Objectives, U.S. Army Command and General Staff College, Fort Leavenworth, Kansas, 2004 https://apps.dtic.mil/dtic/tr/fulltext/u2/a428903.pdf

Lucas, James, Kommando: German Special Forces of World War Two, Cassell Military Classics, London, 1985

Mrazek, James, The Fall of Eben Emael, Presidio Press, 1998

Simon Dunstan, History’s Raiders: The Fall of Fort Eben Emael, The History Channel, 2001, javascript:;

Muder, Wolf, The Attack on Fort Eben Emael: Assault from the Air 10 May 1940 https://www.youtube.com/watch?v=6bfX7v1YCeY

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