 In the later "Tiangong Kaiwu" (The Exploitation of the Works of Nature) treatise, written by Song Yingxing in 1637, the ox bladder described by Jiao Yu is replaced with a lacquer bag and a cord pulled from a hidden ambusher located on the nearby shore, which would release a flint steel–wheel firing mechanism to ignite the fuse of the naval mine.Gunpowder warfare occurred in earnest during the Song dynasty.In China, gunpowder weapons underwent significant technological changes which resulted in a vast array of weapons that eventually led to the cannon.