If I were building the history of Star Fleet in reverse, I'd like the explaination that the
Constitution, NCC-1700, was an upgrade on the prior class of "starship," maybe
Eagle (NCC-956) and all the others on through the NCC-1600's... maybe the earlier ships have similar primary hulls to the Constitutions, with the latter having much more capable secondary hulls and warp drive systems... So maybe Star Fleet decided that instead of building a whole bunch of Constitutions, it would build some (
Constitution, Enterprise, Hood, Lexingtion, Kongo, Yorktown and
Defiant) and simply upgrade the others (
Eagle, Constellation, Republic, Farragut, Intrepid, Potemkin, Excallibur, Exeter... did I miss any?) to Constitution class/status... What d'ya think?