She suffered minor damage during the Battle of Port Arthur at the beginning of the Russo-Japanese War of 1904–05 and supported destroyers as they patrolled outside the harbour.

Renamed Aso by the Imperial Japanese Navy (IJN) she served as a training ship after extensive repairs.

She could carry a maximum of 1,100 long tons (1,118 t) of coal, which gave her a range of 3,900 nautical miles (7,200 km; 4,500 mi) at 10 knots (19 km/h; 12 mph).

[4] Bayan's main armament consisted of two 8-inch (203 mm) 45-calibre guns in single turrets fore and aft of the superstructure.

[5] Anti-torpedo boat defence was provided by twenty 75-millimetre (3.0 in) 50-calibre guns; eight of these were mounted in casemates on the side of the hull and in the superstructure.

[Note 1] Bayan was completed in February 1903[9] and, under the command of Captain 1st Rank Robert Wiren,[10] made port visits in Greece, Italy and North Africa before sailing for Kronstadt.

Bayan was not hit by the initial torpedo-boat incursion and sortied the following morning when the Combined Fleet, commanded by Vice Admiral Tōgō Heihachirō, attacked.

Tōgō chose to attack the Russian coastal defences with his main armament and engage the ships with his secondary guns.

Once her captain realized his mistake, the Russian ship attempted to escape but failed after a Japanese shell struck one of her torpedoes and caused it to detonate.

By this time Bayan had sortied to provide support, but was only able to rescue five survivors before a Japanese squadron of protected cruisers attacked.

Vice Admiral Stepan Makarov led a force of two battleships and three cruisers out to support Bayan and also ordered the rest of the First Pacific Squadron to follow as soon as they could.

Heavily outnumbered, Makarov ordered his ships to retreat and to join the rest of the squadron that was just exiting the harbour.

[16] After bombarding Imperial Japanese Army positions on 27 July, the ship struck a mine[17] and was under repair until September.

[11] After the death of Vitgeft during the Battle of the Yellow Sea on 10 August, Wiren was promoted to rear admiral and became the commander of the First Pacific Squadron.

On 14 March 1909 they began a training cruise that took their naval cadets to the West Coast of the United States and Canada and Hawaii before they returned to Yokosuka on 7 August.