Enterprise B and C

[McAvoy]

Something occurred to me when writing my own histories of Star Trek classes is that there is a big gap between Enterprise-B and Enterprise-D. Enterprise-B we know as being around 2293 and Enterprise-D being 2363. A solid 70 years.

We know that at least with the main line Trek ships that their top dog service life is maybe counted in ten years and maybe twenty.

So what we got is a 70 year gap with Enterprise-C being presumed to be destroyed in 2345. If we go by the twenty year life spans for these ships then Enterprise-B would be replaced by Enterprise-C in 2313. Or you could extend that to 25 years and it would be 2318. Presumably when the B is retired there was another Enterprise in the pipeline. Which you could argue let's say Enterprise-C would be commissioned around let's say 2322. Which would make Enterprise-C 23 years old by the time of Yesterday's Enterprise.

You would think there would be a new class in between Enterprise-C and Enterprise-D. Of course when the Enterprise-C was presumed lost the new Galaxy class was in it's infant stages.

So I have this theory. The Excelsior class was such a dominant class when it came out that Starfleet never tried to find a successor until they really had to. Let's say late 2320's and early 2330's where the Ambassador class was introduced.