1864 or 1865. Deep Bottom, Virginia. Federal gunboat Mendota on the James River. Put in service May 2, 1864. From photographs of the Federal Navy and seaborne expeditions against the Atlantic Coast of the Confederacy. Wet plate glass negative, photographer unknown.
Here’s a pic of a Dahlgren gun drill aboard the Mendota.
UPDATE: If at all interested in this period, be sure read AW1 Tim’s comments on this post. Great stuff.
UPDATE 2: Didn’t realize that the caption was missing. Fixed it.