Steam cannon

A steam cannon is a cannon that launches a projectile using only heat and water. The first steam cannon was designed by Archimedes during the Siege of Syracuse. Leonardo da Vinci was also known to have designed one (the Architonnerre).

The device would consist of a large metal tube, preferably copper due to its high thermal conductivity, which would be placed in a furnace. One end of the tube would be capped and the other loaded with a projectile. Once the tube reached a high enough temperature, a small amount of water would be injected in behind the projectile. In theory, Leonardo da Vinci believed, the water would rapidly expand into vapour, blasting the projectile out the front of the barrel.

The viability of the concept has been explored, with mixed results, by both the television series MythBusters and students at the Massachusetts Institute of Technology.

Age of Steam
Various unsuccessful efforts were made during the age of steam to create working steam machine guns and cannons during the 19th century using methods and technology derived from steam locomotives. A World War II steam cannon was the Holman Projector.