This is a work in progress but finally at least a partial solution to JP's service. I found a record (U.S. Army Registry of Enlistments 1798-1914) that says John Piker enlisted in the regular army at Terre Haute on Dec. 1, 1864 and was assigned to Co. H of the 4th U.S. Artillery. He deserted Oct. 8, 1866 from Reynolds Barracks in D.C., was returned on Oct.10 and deserted, presumably for the final time on January 27, 1867. I have a copy of the court martial file. It's only a couple of pages but he was fined $10/month for 12 months and also 12 months hard labor. Says the sentence will be executed at Ft. Whipple Va. I don't know at the moment whether he escaped or they let him loose early.