I am researching my Great Grandfather's (Hugh Right Callaway) military record and need some assistance to determine his service dates, locations, etc. In the Register of Enlistments (191, record 2939), Hugh Callaway, born in Knoxville, Tennessee joined the Union Army in 1864? at the age of 21 but since he was born in 1848, the age had to be 16. I can't read the remarks section entirely however it shows his alias name as Charles Casier and something about discharges. I would love to know where he served, especially in the Civil War. I located his pension record recently and it shows both his name and alias. He actually has two pension records with his name at the top of one and his alias "Charles Casier" on the top of the other. I deciphered as much as I can from it as follows:

C F & E (Company?) 2nd US Infantry D (Division?) 5 US Artillery
A & I (Company?) 18 US Infantry Sgt(?) Retired USA
06-25-(19)11 25th(?) ??? Dept USA

I can provide a copy of the pension applications and enlistment record I found on Ancestry.com, but I'm not sure where to go from here.
Any recommendations?

It's a mystery about his service since he retired from the US Army after about 40 or so years but the Register of Enlistments shows discharges.
I believe he may have been at Fort Riley, Kansas in the 1890's.
My records show the he was born on August 4, 1848 and died on May 12, 1914.
I would love to see any pictures if any are found.

Thanks,
Morris Callaway