She was assigned to the 5th Division of the 3rd Fleet on 7 January 1918 as its flagship and landed a company of marines in Vladivostok five days later at the start of the Japanese intervention in Siberia during the Russian Civil War. "Iwami" returned to Kure on 9 September and was subsequently relieved from her assignment with the 3rd Fleet. The ship was assigned to defend Kamchatka from 24 September 1920 to 30 June 1921 and was based in Vladivostok and Petropavlovsk. She was reclassified as a first-class coast defense ship in September 1921 and was used as a training ship. In accordance with the terms of the Washington Naval Treaty, Japan agreed to scrap "Iwami". She was disarmed in April 1922 and used as a depot ship until she was struck on 1 September. "Iwami" moored to the west of the island of Jōgashima near the mouth of Tokyo Bay and used as a target by aircraft of the Yokosuka Naval Air Group from 5–8 July, finally sinking on 10 July 1924.