Huo Tong (火桶)

Cutaway drawing of a Huo Tong, from 'Wu Bei Zhi (《武備志》)'.

Huo Tong (火桶, fire barrel), also known as Mai Huo Yao Tong (埋火藥桶, lit. 'Buried gunpowder fire barrel') is a primitive but rather powerful short range naval/siege defence weapon used by Ming navies. It is a large wooden barrel filled with five catties of low grade or spoiled gunpowder (deemed unsuitable for cannon charge) and then covered with a layer of dry sand or soil. A bowl filled with embers covered in ash is carefully placed on top the soil layer just before the barrel is sealed and thrown or dropped onto enemy warship. Once the barrel get knocked over, it will either explode in a burst of flame or spill burning gunpowder everywhere.

Qi Ji Guang (戚繼光) also created an improved version of the weapon that incorporates a wooden rod fuse similar to Zi Mu Chong (子母銃) placed inside a bamboo tube. The improved design allows Huo Tong to be used underwater.