Summer 1942:
One of the world's largest cannon was used in a military intervention for the first time.
"Schwerer Gustav" also named "Dora Cannon" was built in the need for a special weapon to have a suitable super range cannon for the "Ligne Maginot".
From the ordered 3 cannons of this type only one actually had ever been used in combat, it was the battle of Sevastopol (Севастопольская оборона)
The cannon itself was a difficult challenge for maintaining its supplies; within 5 days all its ammunition inventory was depleted.
It was never used anymore after that in combat action.
"Dora-Ensemble"
The projectile in comparison to a T34 tank
Generally it was planned to move the third cannon to Normandy ("Langer Gustav", with some special modifications), to shoot across the English Channel, while "Schwerer Gustav" was planned to move for the battle of Leningrad. But this never happened, instead, the 2 existing cannons were blasted right before proceeding allied troops were able to lay their hands on them, the third never had been finished and was found partly in the remainings of the Krupp factories.
In the video you can also see another special cannon, "Mörser Karl", also especially developed for the "Ligne Maginot" (5 cannons from this type were built).