Henry,

The 12 round/hr rate is correct...I was thinking 5 min/round but crossed units, arg.

Maybe I'm missing the key, but I don't see the CS mortar vessel idea as practical. Operationally they would have been easy prey for monitors which could steam right up and sink them. After all, monitors could get close enough to engage and dismount barbette guns in fortifications. Ignoring monitors, a single steam sloop could charge in and pound a mortar fleet to pieces with relative impunity.

On open water they would likely have been slow and completely inaccurate. Anchored they would be sitting ducks. The Federals used them for stationary bombardment and they were protected by the fleet. The CSA had no such protection to give.

With 10" mortars being insufficient to do the job and the CSA lacking 13" mortars, production and development were problematic. Without the Rodman process, castings for weapons over 10" bore were dicey at best. Anderson at Tredegar didn't succeed in reproducing the process until Fall 1864. The first weapons were being completed in 1865, too late for service.

Leeds in N.O. had trouble casting heavy pieces before the city fell, and it doesn't appear that they could have produced what was needed in time.

Another problem of course was getting engines and boilers for a mortar fleet. This was not something the CSA had much success in doing for other vessels. CS armor clad design was often so underpowered or poorly executed/hampered by poor boilers/engines that a number of the vessels couldn't even stem river current or tides.

I don't see any easy solution to the gunnery problems with the folks and techniques then on hand. Abbot complained late in the war that range tables were not even available for some heavy mortars and he discovered the 1861 models outranged the 1840's considerably at reduced charges because of chamber shape. Even in his tests using carefully orchestrated indirect fire, individual accuracy was poor. The mortars were inherently imprecise so that they would have served as area bombardment even in best case (let alone aboard ships.) Heavy bombardment and imprecise fire would also have been a logistical nightmare for the Confederacy--it was strained to provide heavy artillery projectiles anyway. On the other hand, this was something the Federals could afford.