The Invalid Corps,which would eventually assume the more impressive name of the Reserve Corps, was organized in April 1863 under the control of the Provost Marshal General's Bureau in the War Department.Washinton officials expected the new organization to be one that recognized the valorous service of veteran soldiers who still might serve the nation behind the lines,thus freeing ablebodied men for the front. Members of the corps wore light blue uniform jackets as symbols of honorable past service. The 1st Battalion was for men who could shoulder muskets and perform various tasks that could generally be classified as provost duty. The 2nd Battalion was for less able individuals who could still do hospital or clerical duty.As far as being a substitue, he may have filled in for a family member or in some instances may have been paid by another individual to take his place in the Army.