Federation Commander

I've been reading the background on the 1st generation X-ships, and it mentions that they were converted from existing designs. I was wondering (for a modelling project), what hull were the federation's CXs based on? Was it the basic CA, the NCA, the BCH, the CB, something else, or a totally new design?

They were originally based on the CB; the evolution essentially went from CA > CC > CB > CX.

Module X1R includes an NAX, which was upgraded from the NCA (not an NCC, as there is no flag bridge; as such, the NAX has a lower command rating relative to the CX).

Many thanks, I thought that was probably the case given the naming convention applied to the CXs! Time to start drawing up my evil plans towards the Starline 2500 CB....