The research of heavy shell throwing ordnance and its use in the U.S. Civil War is ongoing. Precedent for Mortar usage just prior to Mr. Lincoln's War in the usage of Mortar vessels converted by the British Royal Navy from dockyard lighters.

The first few of the twenty-two constructed for use in the Crimean Campaign of 1855-56 were conversions, later numbers were purpose built from the outset.

After reading, apon George Wright's mention, Send a Gunboat , Anthony Preston, John Major , 2007 Edition US Naval Institute Press ISBN: 9781591148180 I've followed up on discovery of the small fleet of Mortar vessels mentioned through communication with the National Maritime Museum, UK.

Part of this worthwhile historical site includes photographs at: www.nmm.ac.uk/historicphotographs