Johnston was from Cincinnati, Ohio, and entered the United States Navy, during the American Civil War, in September 1861.
He assisted in the Union gunboat attacks that captured strategic Fort Henry on the Tennessee River 6 February 1862.
1) at Madrid Bend (Tennessee shore) across the river from the Confederate stronghold, Island No. 10.
On 15 February 1864, his gunboat repelled the attack of Confederate raiders, keeping them from saving the town of Waterproof, Louisiana, and securing the federal garrison therein.
Lt. Johnston resigned from the naval service 23 June 1864 and died 23 April 1912 at St. Louis, Missouri.