Ms. Bowers,
For information regarding Co. A, 12th Regiment Indiana Volunteers, please check out the following links:
yesteryear.clunette.com/12thhistoryindex.html and yesteryear.clunette.com/12thhistoryregroster.html
Both are links to an online rendering of Chaplain Gage's published history of the 12th Indiana.
The first link is the index for that history and the second one is a regimental roster. Your husband's GG grandfather is listed therein.
I hope this helps. God Bless you. I remain etc. Perry Ruch