I don't remember much but here's what I do remember: There were two novels featuring a group of elite Union soldiers, both would have been published around 2010, but not later than 2012.
The first novel was set during the civil war and had a steamboat featured heavily.
The second was about one of the soldiers return to his hometown, which was being controlled by a group of outlaws.
One of the group dies in the first book, and they use the rally "Remember____" in the second book.
Two of the group, twins maybe, were very good with explosives.
The slip cover was brown and the title was in the typical western font.