During which war was the leather cannon first deployed?
Guns made from cast iron were too heavy to be moved during battle, and were limited to use in fortresses or on board ships. Guns used in the field were limited to bronze cannon, but only the lightest pieces could be moved during battle. Gustavus Adolphus' tactics were based on the use of effective firepower. Heavy cannon were effective at the start of the battle, but could not be moved once deployed (guns themselves weighed from roughly 300 kilograms to 3 tons). Artillery could not respond effectively to developments in battle.
In order to fill the gap, the leather cannon was developed. A relatively thin copper tube was reinforced by heavy cords and finally clad in leather (alternatively clad in leather straps first and then rope cords). While the weapon was light enough to be mobile (it required only a two-man crew to pull into position and operate, and was cheaper in construction), the basic design proved to be flawed. Reinforcing materials acted as an insulator, not allowing heat to dissipate fast enough. After a few shots the gun would be too hot to use. The heat also deformed the tube and drastically decreased accuracy; once damaged this way, even after being left to cool, the barrel was prone to burst, severely injuring the loader. It was too unreliable to be viable.
But the weapon had achieved one important success – it demonstrated the usefulness of mobile firing.