Leonardo da Vinci proposed the Architonnerre, a steam-powered cannon concept.
The design was intended to heat water inside a sealed chamber. Steam pressure would then propel a projectile from the cannon, replacing the explosive force normally supplied by gunpowder. The name combines classical-sounding terms associated with a powerful artillery device.
Leonardo's idea belongs to his broader investigations of heat, pressure, explosions, and military engineering. It demonstrates that he recognized the force produced when heated water changes into steam, although he did not develop a practical steam engine or establish modern thermodynamics.
The Architonnerre was not a standard Renaissance firearm and is not known to have been successfully deployed. It is also different from Leonardo's multi-barrel weapon, which used many conventional gun barrels. The defining feature here is steam pressure as the proposed launching force.