Er, the USN made 4,5-inch plates for "New Ironsides" and "Roanoke". It was just that 1-inch plates were easier to produce in large quantity (one reason why they stuck with monitors was exactly that they were very manufacturing-friendly). But I guess it just did not have much sense to use costly 4,5-inch plates to re-armor the rather primitive "Atlanta".
Yes But the plate for Ironsides and Roanoke had to be specially cast, Perhaps I should have said 1" laminated plate in common use.
Yep.