A Ming Dynasty Chinese illustration of a naval mine from the 14th century military treatise of the Huolongjing, compiled by Jiao Yu and Liu Ji, with Jiao's preface added in 1412. This particular sea mine was called the 'submarine dragon king' (shui di long wang pao). The firing mechanism consists of a floated incense-stick which lights the fuse when it burns down, this last being contained in a length of goat's intestine, and connecting with the explosive charge which is floated at a certain depth submerged below.