The Battle of Miyako Bay was a naval action on 6 May 1869, in which samurai loyalists of the former Tokugawa shogunate under the flag of the newly formed Republic of Ezo failed to take over the Kōtetsu, the flagship of the Imperial forces of the new Meiji government. It was part of the overall Battle of Hakodate at the end of the Boshin War.

Kōtetsu , later renamed Azuma , was the first ironclad warship of the Imperial Japanese Navy. She was designed as an armored ram for service in shallow waters, but also carried three guns. The ship was built in Bordeaux, France, for the Confederate States Navy under the cover name Sphinx, but was sold to Denmark after the sale of warships by French builders to the Confederacy was forbidden in 1863. The Danes refused to accept the ship and sold her to the Confederates which commissioned her as CSS Stonewall in 1865. The ship did not reach Confederate waters before the end of the American Civil War in April and was turned over to the United States.