 Gunpowder was also applied to arrows in 1206 by a Song army stationed in Xiangyang . The arrows were most likely an incendiary weapon , but its function may also have resembled that of an early rocket . At the Jin siege of Qizhou ( <unk> ) in 1221 , the Jurchens fought the Song with gunpowder bombs and arrows . The Jin <unk> ( <unk> , " iron huopao " ) , which had cast iron <unk> , are the first known bombs that could explode . The bomb needed to be capable of detonating in order to penetrate the iron casing . The Song army had a large supply of incendiary bombs , but there are no reports of them having a weapon similar to the Jin 's detonating bombs . A participant in the siege recounted in the <unk> Qi Qi Lu ( <unk> ) that the Song army at Qizhou had an arsenal of 3000 huopao ( 火礮 ) , 7000 incendiary gunpowder arrows for <unk> and <unk> for bows , as well as <unk> <unk> ( <unk> ) , probably leather bags filled with gunpowder . 
