Further, it is said that Dokan OTA, too, discovered 'Moyuru tsuchi' (flammable dirt), which was considered to be natural saltpeter, in building the Edo Castle, and developed and used weapons using gunpowder such as signal fire or fire arrows, which used 'Moyuru tsuchi' as a material.
また、太田道灌も江戸城築城の際に天然の硝石と思われる「燃土」を発見し、これを用いた狼煙や火箭といった火薬兵器を使用したと伝えられている。