At the start of the Russo-Japanese War, "Azuma" was assigned to the 2nd Division of the 2nd Fleet. She participated in the Battle of Port Arthur on 9 February 1904, when Vice Admiral Tōgō Heihachirō led the Combined Fleet in an attack on the Russian ships of the Pacific Squadron anchored just outside Port Arthur. Tōgō had expected the surprise night attack by his destroyers to be much more successful than it was, anticipating that the Russians would be badly disorganized and weakened, but they had recovered from their surprise and were ready for his attack. The Japanese ships were spotted by the protected cruiser , which was patrolling offshore and alerted the Russians. Tōgō chose to attack the Russian coastal defenses with his main armament and engage the ships with his secondary guns. Splitting his fire proved to be a poor decision as the Japanese eight- and six-inch guns inflicted little damage on the Russian ships, which concentrated all their fire on the Japanese ships with some effect. Although many ships on both sides were hit, Russian casualties numbered some 150, while the Japanese suffered roughly 90 killed and wounded before Tōgō disengaged.