Best of all, the fort's earthen roof made artillery attacks and aerial raids damn nigh pointless. Bombing Eben-Emael was like bombing a well-armed mountain.

Wasily/Wiki Commons
"Nice going, Hans. Now you've pissed off the mountain."

The Fatal Flaw:

The fort could be taken out with just a handful of troops, assuming they could arrive there alive. Which might have been OK, since the whole design should be based on keeping that from happening. But it also turned out that the fort was unintentionally designed to roll out the red carpet for troop-carrying gliders. And we're not talking some fancy, heavily armed wunderwaffe of a glider; no, we mean the unarmed, "prone to flying apart in a whimsical puff of sticks and fabric if you look at 'em funny" type.

Bundesarchiv, Bild 101I-567-1519-18 / Stocker / CC-BY-SA 3.0
Seconds before direct sunlight caused it to burst into flames.

So in the wee hours of May 10, 1940, 11 German Ju 52 planes hauled eleven DFS 230 gliders stuffed with a massive invasion force of 74 paratroopers into the air and flung them toward Eben-Emael like history's deadliest paper airplanes. While the earthen roof of the fort rendered it relatively bomb-proof, it also made for a perfectly cushy landing surface for the gliders, which eschewed wheels in favor of nose skids wrapped in barbed wire to land in a space as short as 20 yards, which is the aircraft equivalent of stopping on a dime.

Once down, taking out the invincible fortress was comically easy: The invaders spilled from the gliders and used hollow charges to funnel devastating explosions down into the base like little reverse volcanoes.

via Wiki Commons
As if volcanoes weren't scary enough in the regular direction.

Yes, just like dropping photon torpedoes down an exhaust port. Once the fort's defenses were more or less taken out, the Nazis blew up the stairwells, trapping the Belgian troops inside. Fortress commander Major Jean Jottrand surrendered the very next day, as his troops poured out of Eben-Emael waving white flags.

A mobile fortress that can be destroyed by two guys with a crowbar sucks at both being mobile and being a fortress. The bombing runs of WWII served to sap armored trains of the final drops of the considerable intimidation factor they had once possessed, because it's hard to be scared of an invasion force that can travel along only one route and can be knocked completely into irrelevancy by a single airplane.

derela.republika.pl
Note the lone crater.

When France fell to Germany in 1940, the Surcouf escaped on one working engine to prowl the Atlantic from Halifax to Connecticut like a goddamned sea monster, even serving with the Free French Naval Forces to liberate the French archipelago of Saint-Pierre and Miquelon in December of 1941.

The Fatal Flaw:

The problem with having a super-massive, gun-bedazzled submarine is that it's really hard to force a giant boat underwater without sinking it. Consequently, Surcouf wasn't exactly a swift diver, and that's a huge problem for a submarine, regardless of how many cannons it has. This mammoth took over two minutes to dive just 40 feet, and when enemy warships and aircraft are hurling ordnance at you, two minutes might as well be forever.

subsim.com
"Oh, you want all this to go underwater?"

That's probably why, while traversing the Gulf of Mexico on the night of Feb. 18, 1942, the Surcouf was literally run over by the American freighter Thompson Lykes while struggling to submerge, and sank with all hands on deck (see "hard to submerge without sinking," above).

Or at least that's the official story. Conspiracy theories abound that the Surcouf actually sank thanks to timed explosives placed on her hull by Royal Navy divers or depth charges from vengeful Nazis, but none of those claims can be proven. So, as far as history is concerned, the Surcouf crashed into another boat in the middle of the night because it sucked at being a submarine.

Though when it comes to embarrassing French naval disasters, that's nothing compared to ...

The Fatal Flaw:

After accompanying Napoleon's army to Alexandria in August of 1798, a French fleet of warships lined up to protect the sorely depleted transport vessels. To keep their literal flagship L'Orient looking suitably imposing, her crew took this downtime as an opportunity to splash a fresh coat of paint on her. That's how, when Cracked-certified badass Horatio Nelson unexpectedly rolled up with a British fleet to kick off the Battle of the Nile, L'Orient's crew found themselves tripping over open tubs of paint and turpentine, a fluid that goes up in angry flames if you so much as breathe on it too heavily. And you know what else is highly combustible? The mountains of gunpowder it takes to feed 120 goddamned cannons.

Still anchored as the British fleet bisected the French line, the paint- and turpentine-soaked L'Orient caught batteries from at least four of the smaller, more maneuverable British ships, unsurprisingly catching fire in the process. When the fire reached the gunpowder, L'Orient went up in an apocalyptic blast that was seen and heard for miles inland, and made the crews of other ships in the bay think their own boats had exploded. That's right -- L'Orient blew up so hard that other people thought they were dead.

Mather Brown
It was like Michael Bay playing bumper boats.

To add insult to injury, after the battle the British scooped up what was left of L'Orient's mainmast and carved it into a coffin, in which Horatio Nelson would eventually rest.

DaysOutGuide.co.uk
"Fuck you, forever." -Horatio Nelson.

The Krupp K5 railway gun and its even more ludicrous big brother, Gustav, were the answer to a specific Nazi quandary: How can we make the biggest gun in the universe and still be able to move it around?

via ww2db.com
They didn't ask themselves this question until they had already started building said gun.

Yes, this was another attempt to build massive weaponry that was intended to ride the rails. Luckily (for the Nazis, not for Europe), Europe was crisscrossed with a system of railways. This gave history's favorite villains the ability to build a weapon large enough to fire a shell the size of two linebackers for distances of up to 50 miles, from anywhere they damn well pleased.

wardocumentaryfilms.com
Its secondary purpose was to infect everyone within a 50-mile radius with shrieking terror shits.

The K5 was one of history's most widely used railway guns, which is another way of saying that the Nazis built over 25 of them. Like a Swiss Army Knife of heavy artillery, it could shell enemy positions, reduce fortresses to rubble, level rioting towns, and even put a serious damper on Allied naval operations, assuming they managed to drag it close enough to a beach.

The Fatal Flaw:

Though it boasted an elevation arc of 50 degrees -- allowing it to target a wide range of distances -- the K5's horizontal traverse was 1 degree. In other words, the gun couldn't turn. It's aiming capabilities ranged from directly in front of it to almost, but not quite, directly in front of it.

ibiblio.org
For reference, there is no possible way the K5 could shoot the building directly next to it.

This problem was compounded by the fact that the K5 was essentially a train -- the only way to get it to face a different direction was to build an entirely new set of tracks for it to run on, not unlike the turntables train stations use to get trains facing in the right direction. Unsurprisingly, these impromptu construction sites made irresistible targets for Allied bombers, for whom railways were the primary objective when explosively demonstrating their air superiority over the Reich. This reduced the K5 (and every other rail gun) to an impressive dust collector, definitively proving that it's not the size of the gun that counts -- it's whether or not you can aim the fucking thing.

worldwartwo.filminspector.com
Cue Madonna's "This Used To Be My Playground."