Battles of Kizugawaguchi

The two Battles of Kizugawaguchi (木津川口の戦い) were fought during Oda Nobunaga's attempted sieges of the Ishiyama Hongan-ji in Osaka. The Hongan-ji was the primary fortress of the Ikkō-ikki, mobs of warrior monks, priests, and farmers who opposed Oda's rule. He ordered one of his admirals, Kuki Yoshitaka, to organize a blockade against the fleets of the Ikki's allies, who sought to supply the fortress and break the siege. Many of the ruling families of the neighboring provinces opposed Oda, chief among them the Mōri clan.

The first battle
In the first battle, in 1576, the Mōri defeated Kuki Yoshitaka's fleet, breaking the blockade and supplying the fortress. Both sides fought with firearms, a rather new development in Japanese warfare; but Mōri's experience and knowledge of naval tactics was ultimately the deciding factor.

The second battle
Two years later, the Ishiyama Hongan-ji was still under siege, and Oda's fleet, commanded once again by Kuki Yoshitaka, made another attempt to break the Mōri supply lines. Going against convention, Yoshitaka fought with six very large ō-adakebune ships, rather than a combination of small (kobaya), medium (sekibune), and large (adakebune) craft. Normally, adakebune were essentially wooden floating fortresses, covered in gun and bow emplacements. According to some accounts, it may be believed that these six were the first ironclads, and were built such that guns could not penetrate them. However, rather than true ironclads, made primarily or entirely of metal, these craft probably simply had limited iron plating in key locations.

Several Mōri vessels were burned and sunk, and Oda's fleet ultimately achieved victory. The supply lines were broken, and the Hongan-ji fell soon afterwards. However, during this battle an interesting flaw was discovered in the ō-adakebune design. As Mōri samurai rushed to board the large ship, all the defending warriors ran to that side of the deck, to defend themselves, and the ship capsized as its center of gravity shifted.

Yoshitaka went on to defeat the Mōri once more the following year.