Leonardo da Vinci’s proposed rapid-fire weapon used an array of 33 barrels.
The concept is commonly described as a 33-barrel organ, because the barrels were arranged in groups on a frame and resembled the pipes of a musical instrument. The intended advantage was that one group could be fired while another cooled or was reloaded, creating a more sustained sequence of shots than a single muzzle-loading gun.
The weapon was a design study, not a proven battlefield system. Renaissance gunpowder weapons were limited by slow loading, smoke, recoil, and the difficulty of moving heavy equipment. The 33 barrels were also not the same thing as a modern machine gun, which uses a continuous or mechanically assisted firing system.
Leonardo’s drawing shows his interest in solving practical military problems through arrangement and timing, not only through a new projectile.