In Leonardo's notebooks there is an array of war machines which includes a tank to be propelled by two men powering crank shafts. Although the drawing itself looks quite finished, the mechanics were apparently not fully developed because, if built as drawn, the tank, with a lot of effort, might be made to rotate on the spot, but would never progress in a forward direction. In a BBC documentary, a military team built the machine and found it not working, until they changed only one of the gears. It is believed that Da Vinci deliberately left this error in the design, in order to prevent it from being put to practice by unauthorized people.
Another machine, propelled by horses with a pillion rider, carries in front of it four scythes mounted on a revolving gear, turned by a shaft driven by the wheels of a cart behind the horses.
Leonardo's notebooks also show cannons which he claimed "to hurl small stones like a storm with the smoke of these causing great terror to the enemy, and great loss and confusion."
He also designed an enormous crossbow. Following his detailed drawing, one was constructed by the British Army, but could not be made to fire successfully.
Leonardo was the first to sketch the wheel-lock musket c. 1500 AD (the precedent of the flintlock musket which first appeared in Europe by 1547), although the Chinese of the earlier 14th century had used a flintlock 'steel wheel' in order to detonate land mines.
[Leonardo] wanted to increase the rate of firing weapons and so designed machines with multiple cannons, so they could be fired successively or all together. Many people consider these the forerunner of the modern machine gun. Two of these used racks of eleven or fourteen guns. While the top row was being fired the next rack was loaded; at the same time, a third rack was cooling off. Another design had the guns in a triangle spread for greater distribution of the projectiles.