At the Battle of the Sea of Japan in the Japanese-Russo War, MIKASA fought valiantly as the flagship of the Combined Fleet under Admiral Heihachiro Togo, Commander-in-Chief of the Combined Fleet. ADM Togo always led the fleet and fought daringly against the Russian Fleet which was deployed from the Baltic Sea, and greatly contributed to this historic and overwhelming victory in the history of the naval battle.

While MIKASA was in the port of Sasebo after the battle, she sank unfortunately due to an accidental explosion in her shell magazine, but she was re-floated and repaired. Then she returned to the front line and accomplished her mission of the maritime defense. Although in 1923 the Washington Naval Conference proposed that MIKASA was to be decommissioned and scrapped, the Conference approved to preserve her as a memorial ship. In 1926, MIKASA turned out to be a commemorative Memorial Ship at the current location after her renovation for a year and half.

Battle of the Sea of Japan
At 13:39 p.m., May 27th, 1905, the main force of the Japanese Fleet sighted the Russian Baltic Fleet approaching from the southwest in two lines ahead at a distance of approximately 13km. ADM Togo decided to attack the enemy fleet from the front port line, while he headed his fleet westward. At 13:55 p.m., ADM Togo hoisted the famous "Z" Signal Flag Meaning "The rise and fall of the Empire depend on this battle. Let every man do his utmost." At 14:02 p.m. ADM Togo set the course of the Fleet to the southwest, took the position of reverse action run to the port side, and started to close in heading southward.
ADM Togo, standing on the MIKASA's bridge with his left hand holding noted sword forged by the great sword smith, a gift from The Crown Prince, started at the rapidly approaching enemy fleet and waited for the right opportunity to bear down the enemy's leading ship. At 14:05 p.m., with the enemy front at 8 km, he gave the order for a great turn, so called "Togo-Turn."