 The Song official Yu <unk> was in command of the army defending the river . The Jurchen army was defeated while attacking Caishi between November 26 and 27 during the Battle of Caishi . The <unk> @-@ wheel ships of the Song navy , armed with <unk> that fired gunpowder bombs , overwhelmed the light ships of the Jin fleet . Jin ships were unable to compete because they were smaller and hastily constructed . The bombs launched by the Song contained mixtures of gunpowder , lime , scraps of iron , and a poison that was likely arsenic . Traditional Chinese accounts consider this the turning point of the war , characterizing it as a military upset that secured southern China from the northern invaders . The significance of the battle is said to have rivaled a similarly revered victory at the Battle of Fei River in the 4th century . Contemporaneous Song accounts claimed that the 18 @,@ 000 Song soldiers commanded by Yu <unk> and tasked with defending Caishi were able to defeat the invading Jurchen army of 400 @,@ 000 soldiers . Modern historians are more skeptical and consider the Jurchen numbers an exaggeration . Song historians may have confused the number of Jurchen soldiers at the Battle of Caishi with the total number of soldiers under the command of Wanyan Liang . The conflict was not the one @-@ sided battle that traditional accounts imply , and the Song had numerous advantages over the Jin . The Song fleet was larger than the Jin 's , and the Jin were unable to use their greatest asset , cavalry , in a naval battle . 
