Thanks, Max.
Cannonmn,
What would also tend to give more credence to this article is that it appears like its copying verbatim a document that was written by the "Chief of the Bureau of Ordnance of the Navy Department."
It would also be simpler if there was only one designation for this cannon: So far I've seen it named the '3-inch steel boat gun', 'light howitzer of 350 pounds', 3-inch breech loading howitzer', etc..