Battle of Caishi participant Yu Yunwen
The Battle of Caishi (Chinese: 采石之戰) was a major naval engagement of the Jin–Song Wars of China that took place on November 26–27, 1161. It ended with a decisive Song victory, aided by their use of gunpowder weapons.
Soldiers under the command of Wanyan Liang, the emperor of the Jurchen-led Jin dynasty, tried to cross the Yangzi River to attack the Southern Song dynasty.
Chen Kangbo, prime minister of the Song dynasty, was chief military strategist and commanded the navy. Yu Yunwen, a civil official, commanded the defending Song army. The paddle-wheel warships of the Song fleet, equipped with trebuchets that launched incendiary bombs made of gunpowder and lime, decisively defeated the light ships of the Jin navy.Overview
Starting in 1125 the Jin had conquered former Song territories north of the Huai River. In 1142, a peace treaty settled the border between the two states, putting the Jin in control of northern China and the Song in control of the south. In 1150, Wanyan Liang became emperor and planned to unite northern and southern China under a single emperor. In 1158, he asserted that the Song had violated the 1142 treaty, a pretext for declaring war on the Song. He prepared for the war in the following year. He instituted a draft where all able-bodied men were required to enlist. The draft was unpopular, precipitating revolts that were later suppressed. The Jin army left the capital of Kaifeng on October 15 1161, and pushed through from the Huai to the Yangzi. 
The Song were fortified along the Yangzi front. Wanyan Liang planned to cross the river at Caishi, (modern day Ma'anshan) south of modern-day Nanjing. He embarked from the shore of the Yangzi on November 26, and clashed with Song forces led by Yu Yunwen and Chen Kangbo in a naval engagement. Wanyan Liang lost the battle and retreated to Yangzhou. 
Wanyan Liang was assassinated in a military camp by his own soldiers shortly after the Caishi battle. A military coup had taken place in the Jin court while Wanyan Liang was absent, enthroning Emperor Shizong as the new emperor. A peace treaty signed in 1165 ended the conflict between Song and Jin.
At Caishi, the Song led an army of 18,000, whereas Wanyan Liang reportedly led an army of 600,000 Jin soldiers. Over the course of the battle, many Jin soldiers deserted—bringing down the total Jin force—as they realized their northern steppe cavalry was inadequate for naval battles on rivers and lakes. The Song won mainly through its superior navy, gunpowder, and firearms. The victory boosted the morale of the Song infantry and pushed back the southern advance of the Jin army.Song preparations for Caishi
Diplomatic exchanges between the Song and Jin did not stop during the period preceding the war. The History of Song claims that the Song realized that the Jin were planning for an invasion when they noticed the discourtesy of one of the Jin diplomats. Some Song officials foresaw the impending war, but Emperor Gaozong hoped to maintain peaceful relations with the Jin. His reluctance to antagonize the Jin delayed the fortification of the Song border defenses. The Song quickly built just three military garrisons in 1161. Wanyan Liang departed from Kaifeng on 1161 October 15. The offensive comprised four armies, and Wanyan Liang personally led the army that entered Anhui. The Jin passed the Huai River boundary on October 28, advancing into Song territory. The Song resistance was minimal because they had fortified the southern shore of the Yangzi River and not the Huai.Chen Kangbo (陈康伯), prime minister (宰相) of the Song dynasty, commanded the Song navy and designed the anti-Jin offensive strategy. Yu Yunwen, a civil official, commanded the defending Song army. The paddle-wheel warships of the Song fleet, equipped with trebuchets that launched incendiary bombs made of gunpowder and lime, decisively defeated the light ships of the Jin navy.Naval battle of Caishi
Wanyan Liang's army built its encampment near Yangzhou on the northern side of the Yangzi River. The Jin advance had been slowed by Song victories in the west, where the Song captured several prefectures from the Jin. Wanyan Liang commanded his forces to cross the Yangzi at Caishi, south of modern Nanjing. A naval battle between Jin and Song took place on November 26 and 27, 1161.The Song strategy was planned by Chen Kangbo (陈康伯), prime minister and naval leader of the Song dynasty. Chen led a naval regiment of his own, dispatching general Yu Yunwen (a scholar-official), his lieutenants Dai Gao, Jian Kang, Shi Zhun, and others to lead the rest of the army. Yu, who was a Drafting Official of the Secretariat (Chinese: 中書舍人; pinyin: zhongshu sheren), was at Caishi to distribute awards to Song soldiers who had been selected for their outstanding service. It was by chance that his visit coincided with Wanyan Liang's campaign. When Yu first arrived, there were various scattered Song forces at Caishi, so Yu took command and built a cohesive unit.The Jin performed a ritual sacrifice of horses a day before the battle (animal sacrifice). On November 26, Jin troops embarked from the shore of the Yangzi and engaged the Song fleet. Some of the ships they boarded were shoddily built. The Jin had lost several ships in Liangshan, where they were bogged down by the shallow depths of Liangshan Lake as they were being transported to the Grand Canal. Wanyan Liang had urgently requested the construction of more ships in 1161 to compensate for those still stuck in Liangshan. One account of the war contends that the Jin ships were constructed in a week with materials recycled from destroyed buildings. The shortage of vessels and the poor quality of those available prevented the Jin from ferrying more soldiers needed for fighting a naval battle with the Song.The Song military response was stronger than Wanyan Liang had anticipated. The paddle-wheel ships of the Song navy could move more rapidly and outmaneuver the slower Jin ships. The Song kept their fleet hidden behind the island of Qibao Shan. The ships were to depart the island once a scout on horseback announced the approach of the Jin ships by signaling a concealed flag atop the island's peak. Once the flag became visible, the Song fleet commenced their attack from both sides of the island. Song soldiers operated traction trebuchets that launched incendiary "thunderclap bombs" and other soft-cased explosives containing lime and sulphur, which created a noxious explosion when the casing broke. The Jin soldiers who managed to cross the river and reach the shore were assaulted by Song troops waiting on the other side. The Song won a decisive victory. Wanyan Liang was defeated again in a second engagement the next day. After burning his remaining ships, he retreated to Yangzhou, where he was assassinated before he could finish preparations for another crossing.
One [the middle squadron] was stationed in midstream. These carried our elite troops to meet the attack. The remaining two squadrons were hidden in creeks to serve as reserve. Barely was the arrangement completed when suddenly we could hear the shouts of the Tatar hordes. The Tatar chieftain, holding a small red flag, ordered several hundred of his boats to cross the river. In a short time, seven boats reached the south bank. The Tatars leaped ashore and fought with the government troops. Your minister walk[ed] back and forth in our ranks, again and again exhorted our men about their great duty and also promising them rewards. Our men fought desperately, and after all the enemy [ashore] had been killed or taken prisoner, the battle continued on the river. Our large warships then attacked and sank many of the Tatar boats. Enemy troops who were drowned or killed are estimated to be as many as ten thousand. As darkness came, the sound of drums gradually quieted, and the Tatars fled in their remaining boats.
Another account tells of General Chen Lugong (Chen Kangbo)「陈鲁公（陈康伯）采石」and how he also led naval regiments to defeat the Jin and defend the Song.