After the United States entered World War I in April 1917, the ship was used primarily to train gunners and engine room personnel, as the US Navy had expanded significantly to combat the German U-boat campaign. She escorted convoys in late 1918, and after the war ended she took part in the effort to bring American soldiers back from France. "New Hampshire" remained in service for only a few years after the war, as the 1922 Washington Naval Treaty significantly reduced the navies of the signatories; as a result, the ship was sold for scrap in November 1923.