It IS true that the Union decided on the monitor "style" of ironclad as the Confederate forces decided on the "casemate" style....there was only one USS Monitor is also true, and the CSS Virginia (formerly the USS Merrimack...a captured Union frigate converted into the ironclad)...but both sides had many different ironclads to fight with, monitor style AND casemate style. The Union ALSO used a "casemate" style in their riverboat ironclads and "tinclads"...which had NO metal armor, but rather a heavy wooden bulwark for protection...."Google" is a good friend in this case.
I only bring this up, as I learned a lot when I did research for the scratch built ironclads I built, and have shown on this site....the fast pace of the conversions for war were incredible!!
Besides, in OUR world of gaming, ANYTHING is possible AND plausible!
Anyway...my 2 cents
Cheers,
Carl