In 1934, the only thing standing in the way of the Nazis invading France was the Maginot Line, a fortification running from the Rhine River to La Ferté made of concrete blockhouses, bunkers, and rail lines.

The line was elaborate and extensive, and as rumors of its strength traveled to Germany, Hitler began to believe he'd need a miracle for his troops to break through it.

So, the German High Command commissioned engineers to design a weapon powerful enough to break through the concrete fortifications that were nearing completion.

The shells alone had to be strong enough to penetrate 22 feet of reinforced concrete and at least three feet of steel plating, meaning the weapon was likely to be massive.⁠

What they ended up with was Schwerer Gustav — a weapon that was almost four stories tall, 150 feet long, and weighed over 1,300 tons.