Very impressive for its day .... even now !
They certainly were determined.

https://militaryhistoria.com/schwerer-gustav/

Those Germans ...always over-doing things.

Put that in your 6.5 CM pipe and smoke it

Wonder how many grains of what Retumbo that took after they found the searing depth? Lol

It's hard to imagine what an incoming shell from that thing would sound like and what the detonation would be like. Even if it landed outside of killing/crippling range it would have been terrifying.

In the article .....

A Range of 29.2 miles
The Schwerer Gustav fired two types of shells: armor-piercing (AP) and high explosive (HE). Crews fired the 11-foot-10-inch (3.6-meter) long AP rounds with 4,630 pounds (2,100 kg) of propellant. Made of chrome-nickel steel, these rounds weighed 15,653 pounds (7,100 kg) and contained 551 pounds (250 kg) of explosives.

They achieved a muzzle velocity of 2,362 feet per second (720 meters per second) and a maximum range of 23.6 miles (38 km). At maximum range, the AP projectile reached approximately 39,370 feet (12 km) in altitude and stayed airborne for two minutes.

The 13-foot-9-inch (4.2-meter) long HE ammunition, fired with 4,938 pounds (2,240 kg) of propellant, weighed 10,582 pounds (4,800 kg) and carried 1,543 pounds (700 kg) of explosives. These rounds had a muzzle velocity of 2,690 feet per second (820 meters per second) and a maximum range of 29.2 miles (47 km), creating craters about 33 feet (10 m) wide and deep upon impact.