The Paris gun or ParisGeschütz were long range artillery guns designed to bombard Paris during World War 1.

It had the distinction of being the highest range projectile fired during WW1. The gun pushed artillery technology to the limit and the shells reached stratospheric altitudes to cover such long distances. Little was known about the technology since the guns and plans were destroyed. However the engineer's notes were discovered by Gerald Bull 70 years later.

If you want to read more about this topic, some links & books below:

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

Superguns
https://ospreypublishing.com/supergun...
by Steven Zaloga

Paris Kanonenthe Paris Guns (Wilhelmgeschütze) and Project HARP: The Application of Major Calibre Guns to Atmospheric and Space Research 1988
Book by Charles H. Murphy and Gerald Bull