Battle of Lang-shan Jiang

The Battle of Lang-shan Jiang (狼山江之戰) was a naval (river) battle which occurred in 919 (not 932 as is often cited) during the Five Dynasties and Ten Kingdoms period in China between the states of Wuyue and Wu.

Forces
The two forces would appear equal, roughly 500 dragon ships on each side(see dragon boat for more). The Wuyue were commanded by Wen-Mu-King and the Wu by Chien Yuan Kuan. The Wuyue had an ace, a double pump flamethrower. This flamethrower may have used gunpowder to ignite the petrol (Greek fire). Wen-Mu-King apparently had the flamethrower (or flamethrowers) decorated with silver so that if the enemy captured it they'd take the silver and leave the petrol and apparatus.

Battle
The Wuyue managed to destroy with their flamethrower 400 enemy ships then captured 7000 prisoners.

Analysis of battle
The source describes both sides as having "dragon like ships". These could simply be normal war boats with dragon heads carved on. However, in Chinese culture, there are canoes with dragon heads which are used for various sporting events, in honour of an ancient Chinese philosopher. If they were using these types of boat, then it could be that normal military equipment (i.e. warships) was in short supply, and considering the chaos of this time, that could be possible. This could be the reason why they started inventing the flamethrowers, since oil at this stage was quite abundant in the rocks around some parts of China. We know from the Wujing Zongyao from 1044 that at that stage fire drug (proto-gunpowder) was being used to ignite oil from flamethrowers. It could therefore be, that in the chaos, Wen-Mu-King may have started using what was then a type of medicine (or at the most, entertainment) as a slow match for his flamethrowers.

Aftermath
The flamethrower would go on to be an effective but dangerous weapon for the Chinese. Gunpowder (probably already used in incendiary arrows and primitive grenades (see Early thermal weapons) would go on to be used in more effective and terrorizing ways in China and the world.

Source

 * Joseph Needham. Science and Civilisation in China V7:5 the Gunpowder Epic