Shui Di Long Wang Pao (水底龍王砲) and Hun Jiang Long (混江龍)

Shui Di Long Wang Pao (水底龍王砲, lit. 'Underwater dragon king bomb')

Drawing of Shui Di Long Wang Pao, from 'Wu Bei Zhi (《武備志》)'.

Shui Di Long Wang Pao was a drifting naval mine used by the Ming military. Designed for riverine warfare, the mine was usually deployed upriver under the cover of the night, so that it could naturally drift downstream towards moored enemy ships. 

Shui Di Long Wang Pao consistd of several components: a four to six jin wrought iron bomb placed inside a lacquered (waterproofed) cow bladder, which was fixed on top of a wooden plank or miniature raft. Several stone weights were tied to the underside of the plank, serving as its ballast. The stones were heavy enough to submerge the mine, but not too heavy as to cause it to simply sink to the bottom of the river. An incense fuse inside a waterproofed tube made of goat intestine was connected to the bomb at one end, and connected to a small wooden plank attached with goose feathers at the other end. This was to ensure the incense stays afloat and dry, as well as having enough air to stay lit.

Despite these waterproofing features, Shui Di Long Wang Pao was still somewhat unreliable. Both the bomb and its fuse were susceptible to underwater debris and unpredictable river currents/waves, not to mention the incense sometimes went out due to insufficient oxygen.

Hun Jiang Long (混江龍, lit. 'River-muddling dragon')

Schematic of Hun Jiang Long, from 'Tian Gong Kai Wu (《天工開物》)'. 

Hun Jiang Long was the anchored version of Shui Di Long Wang Pao. First recorded by Song Ying Xing (宋應星) in his phenomenal encyclopedia Tian Gong Kai Wu (《天工開物》) in 1637,  this weapon probably saw service for quite some time even before that, as weapons based on identical principle and application were already in use as early as 1549.

Hun Jiang Long differed from its drifting counterpart in that it packed a friction-wheel mechanism similar to Gang Lun Fa Huo (鋼輪發火) together with the bomb into the cow bladder. It also did away with the fuse, replacing it with a cord connected to the trigger mechanism. The cord extended to the river bank and was manually pulled by an operator.