Cant Combine Dreadnoughts?

Just tried to build a Dreadnought squadron fro the first time. Message said " first fleet has dreadnought". Please, please someone tell me that there is a special way to create dreadnought fleets…

DNs must always be the flagship.

I changed category to game help.

Your not supposed to be able to you can only have one dread per fleet

^^^ yup 1per fleet