The two Battles of Kizugawaguchi (木津川口の戦い, Kizugawaguchi no Tatakai^?) 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.

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.

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.

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