Duane --

So you knew all along - Co. "A", 37^th Wisconsin Regiment. Hartman was wounded in his regiment's first battle just outside Petersburg VA on June 18, 1864. Losses in the attack on the Norfolk-Petersburg railroad cut were quite heavy.

Here's an account of the regiment --
http://www.twsgraphics.com/genealogy/WIS37thInf.htm

Check for images at the Wisconsin State Archives. Copies of Hartman's military service file are available here --