Machine Gun by Leonardo Da Vinci
The aim of the tiers is that in rotation, the first tier is fired while the second tier can be loaded. This allows for the third tier to cool down before its turn in the rotation to be loaded and fired again.
Leonardo always aimed to increase the firepower of the weapons he worked on and to maximize their overall destructive capacity. He did this for both his Patronís benefit in having superior firepower compared to his rivals and for his own personal, intellectual curiosity.