In Kumano, large, impressive warships were used during the Muromachi and Edo periods. These warships were called "Atakebune" or "Atagibune." Ranging from 300 tons for large ships to 75 tons for small ships, they were equipped with 50 to 160 oars. To protect against gunfire, the 300-ton, were surrounded by thick wooden shields on all sides, and each shield was hinged to allow it to be freely opened and closed. While they would attack in battle by opening these shields for a volley of gunfire or arrows, they were crewed by more than 100 sailors to pull the oars, plus over 100 samurai warriors for fighting, so they are best described as flagships commanded by generals. These warships have long been reputed to have originated from Atagi in the town of Shirahama, Nishimuro District. In the middle part of the Nanboku period, the Atagi clan based there controlled the Kii Channel, which ex-tended seaside the provinces of Awa, Awaji, and Kishu, and gave rise to the age of the Kumano Navy.

The Gempei War is a famous incident in history. You can experience part of this historical drama at Sandanbeki. During the fierce fighting between the Minamoto and Taira clas, the Kumano Navy entered the Gempei War under the command of Kumano Betto Tanzo (the father of Musashibo Benkei), which is said to have as to the resounding victory by Minamoto clan.