[1] He enlisted as a private in Company C of 9th Pennsylvania Reserve Regiment on July 27, 1861.
[2] He earned his medal in action the Battle of Antietam, Maryland on September 17, 1862.
[2] Following Antietam, Johnson was granted the Medal of Honor and a promotion to second lieutenant.
[2][3] He was transferred to the Veteran Reserve Corps in 1863 as stated in General Order No.160 on May 30, 1863.
[3] For extraordinary heroism on 17 September 1862, in action at Antietam, Maryland, for individual bravery and daring in capturing from the enemy two colors of the 1st Texas Rangers (Confederate States of America), receiving in the act a severe wound.