With the start of the Russo-Japanese War in February 1904, "Shinano Maru" was one of the first ships requisitioned by the Imperial Japanese Army for use as a troopship and military transport to convey troops and supplies to Korea and Manchuria. In March 1905, "Shinano Maru" was armed and converted into an auxiliary cruiser at Kure Naval Arsenal, mounting two guns (one fore and one aft), and was commissioned into the Imperial Japanese Navy under the command of Captain Morikawa. Shortly before the Battle of Tsushima she was assigned to the Auxiliary Squadron of the Combined Fleet along with six other armed merchantmen and three torpedo boat tenders assigned to patrols of the Tsushima Strait to search for the Russian Baltic Fleet, which had been dispatched around the world to relieve the Japanese blockade of Port Arthur.