The 1580 battle of Omosu (重須の戦い, Omosu no Tatakai) was one of many battles fought between the Hōjō and Takeda clans during Japan's Sengoku period. It is distinguished, however, as one of the very few naval battles to be fought in pre-modern Japan.

Battle of Omosu
DateMarch 1580
Location35°01′12″N 138°53′17″E / 35.020°N 138.888°E / 35.020; 138.888
Result Hōjō victory
Hōjō forces Takeda forces
Commanders and leaders
Hōjō Ujimasa
Fūma Kotarō
Takeda Katsuyori
Ohama Kagetaka
Battle of Omosu is located in Shizuoka Prefecture
Battle of Omosu
Location within Shizuoka Prefecture
Battle of Omosu is located in Japan
Battle of Omosu
Battle of Omosu (Japan)

The battle took place off the coast of the Izu peninsula between the navies of Hōjō Ujimasa, the head of the Hōjō, and those of Takeda Katsuyori, the head of the Takeda.

The Fūma ninja led by Fūma Kotarō covertly infiltrated and attacked a camp of the Takeda clan forces at night, succeeding in causing severe chaos in the camp, which resulted in massive casualties among the disoriented enemies as they attacked each other.[1][unreliable source?]

Later, while the navies faced off, the land armies of each family advanced towards one another.[2] In the end, the Hōjō were victorious.


  1. ^ Joel Levy, Ninja: The Shadow Warrior, p.165-166.
  2. ^ Turnbull, Stephen (2000). The Samurai Sourcebook. London: Cassell & C0. p. 230. ISBN 1854095234.