Federal.
Bringing together the previous post and this post about grenades, here is an interesting account from a Tennessee River squirmish in 1865. Has anyone ever seen or heard of one of those odd river grenades?
(From Official records of the Union and Confederate Navies in the War of the Rebellion. ; Series I - Volume 27: Naval Forces on Western Waters (January 1, 1865 - September 6, 1865); Supply Vessels (January 1, 1865 - September 6, 1865))