From Boston Globe 1924 "The Drummer Boy of Shiloh," William Henry Mershon who served during the Civil War in Company I, 30th Regiment Indiana Volunteers and the 15th Regiment of the Veterans Reserve Corps from September 13, 1861 to November 11, 1868.
I also found a site with Ambrotype of William Henry Mershon, "The Drummer Boy of Shiloh," holding his Navy revolver. Photo was taken in April 1861 about three weeks after he captured a Rebel Colonel,at the battle of Shiloh. He used this gun, given to him by Captain White, his captain in the 30th Infantry Regiment of Indiana Volunteers, shortly after he enlisted. The #2 is a mark he placed as a reference # to be used in the writing of a book about him. Included is a Certificate of Authenticity and Biography. https://www.liveauctioneers.com/item/485931_195-photograph-ambrotype-civil-war-wh-mershon