Prototype Nazi multistage cannon ('V-3'), Occupied Poland, 1942

Per Wikipedia:

The V-3 (German: Vergeltungswaffe 3, ("Vengeance Weapon 3") was a German World War II large-caliber gun working on the multi-charge principle whereby secondary propellant charges are fired to add velocity to a projectile, built in tunnels and permanently aimed at London, England.

The Germans planned to use the weapon to bombard London from two large bunkers in the Pas-de-Calais region of northern France, but they were rendered unusable by Allied bombing raids before completion. Two similar guns were used to bombard Luxembourg from December 1944 to February 1945.

The V-3 was also known as the Hochdruckpumpe ("High Pressure Pump," HDP for short), which was a code name intended to hide the real purpose of the project. It was also known as Fleißiges Lieschen ("Busy Lizzie").

They detail the shelling of Luxembourg in the article.

I really wish there was a way for the Germans to keep coming up with their wacky inventions without the whole death, murder and, suffering part. WW2 Germany was coming up with some insane "how did you even think of this" shit. And sometimes it worked.

Iraq was working on one as well though many years later

https://en.wikipedia.org/wiki/Project_Babylon