The introduction of the iron bomb was significant to the history of gunpowder weaponry. Traditionally the inspiration for the development of the iron bomb is ascribed to the tale of a fox hunter named Iron Li. According to the story, around the year 1189 Iron Li developed a new method for hunting foxes which used a ceramic explosive to scare foxes into his nets. The explosive consisted of a ceramic bottle with a mouth, stuffed with gunpowder, and attached with a fuse. Explosive and net were placed at strategic points of places such as watering holes frequented by foxes, and when they got near enough, Iron Li would light the fuse, causing the ceramic bottle to explode and scaring the frightened foxes right into his nets. While a fanciful tale, it's not exactly certain why this would cause the development of the iron bomb, given the explosive was made using ceramics, and other materials such as bamboo or even leather would have done the same job, assuming they made a loud enough noise. Nonetheless, the iron bomb made its first appearance in 1221 at the siege of Qizhou (in modern Hubei), and this time it would be the Jin who possessed the technological advantage. The Song commander Zhao Yurong (趙與褣) survived and was able to relay his account for posterity.
Qizhou was a major fortress city situated near the Yangtze and a 25 thousand strong Jin army advanced on it in 1221. News of the approaching army reached Zhao Yurong in Qizhou, and despite being outnumbered nearly eight to one, he decided to hold the city. Qizhous arsenal consisted of some three thousand thunderclap bombs, twenty thousand "great leather bombs" (皮大炮), and thousands of gunpowder arrows and gunpowder crossbow bolts. While the formula for gunpowder had become potent enough to consider the Song bombs to be true explosives, they were unable to match the explosive power of the Jin iron bombs. Yurong describes the uneven exchange thus, "The barbaric enemy attacked the Northwest Tower with an unceasing flow of catapult projectiles from thirteen catapults. Each catapult shot was followed by an iron fire bomb [catapult shot], whose sound was like thunder. That day, the city soldiers in facing the catapult shots showed great courage as they maneuvered [our own] catapults, hindered by injuries from the iron fire bombs. Their heads, their eyes, their cheeks were exploded to bits, and only one half [of the face] was left." Jin artillerists were able to successfully target the command center itself: "The enemy fired off catapult stones ... nonstop day and night, and the magistrates headquarters [帳] at the eastern gate, as well as my own quarters ..., were hit by the most iron fire bombs, to the point that they struck even on top of [my] sleeping quarters and [I] nearly perished! Some said there was a traitor. If not, how would they have known the way to strike at both of these places?"
Zhao was able to examine the new iron bombs himself and described thus, "In shape they are like gourds, but with a small mouth. They are made with pig iron, about two inches thick, and they cause the city's walls to shake." Houses were blown apart, towers battered, and defenders blasted from their placements. Within four weeks all four gates were under heavy bombardment. Finally the Jin made a frontal assault on the walls and scaled them, after which followed a merciless hunt for soldiers, officers, and officials of every level. Zhao managed an escape by clambering over the battlement and making a hasty retreat across the river, but his family remained in the city. Upon returning at a later date to search the ruins, he found that the "bones and skeletons were so mixed up that there was no way to tell who was who."