The Chu-Ko-Nu is a repeating
crossbow that can shoot 10
arrows with
steel tips in rapid succession. It is operated by moving a lever foreward and backward. The bolts drop down from a box mounted on the crossbow, while moving backwards it first tensions the bow string, then shoots the bolt.
The Chu Ko Nu was often mounted on castle walls, since it is not terribly accurate due to the movement of the arms of the crossbowman. If refilled with more bolts by a second person, it would be able to shoot without a break.
It was used in the Manchurian dynasty and is based on a previous design, the lien nu or ts'an lien, which shoots four bolts and was known as early as 250 BC.