In the episode "Up the Long Ladder", the drive type for the S.S. Mariposa
was Yoyodyne Pulse Fusion. Here is an article from Wikipedia on what I think this could be, which is antimatter catalyzed nuclear pulse propulsion. (http://en.wikipedia.org/wiki/Antimat...lse_propulsion
Realistically, the Phoenix
, or the Bonaventure
, would have a drive type less advanced than the Mariposa
, but would still be capable of bringing a ship to warp.
If I take into account that the Republic
was powered by nuclear reactions, and was being used for training, and the fact that ships were faster in the 2250s than in the 2230s, I think that the shift to the matter-antimatter warp system occurred in the mid-23rd century. The first ships to have this system, that we know of, were the Connies.
For me, there is something else to consider. Impulse is synomous in Star Trek with nuclear-powered engines. The S.S. Valiant
and the Romulan Bird-of-Prey were both described as having impulse, yet were described or shown to be interstellar ships. So, these ships in my interpretation had a primitive warp drive that involved a nuclear reaction of some kind.
I agree that Enterprise was an attempt at retroactive continuity.