My Great grandfather was in the 12th, Co. E.,the same as your GG grandfather. Company E was formed in Ellis County, Texas (they were also known as the Ellis County Grays). James C. Brown was the Captain. The two books recommended are probably the best available on the subject of the 12th. The 12th was a cavlary unit, primarily scouts (or spies as they called themselves). The 12th did participate in several battles, all West of the Mississippi (Louisiana and Arkansas). Most of the men in Company E were from Ellis County, although some, like my great grandfather were from Navarro County. Where is your gg grandfather from?