Robert Comsol wrote:
During Nelson's/Hornblower's era of the Royal Navy the sailing ships were mostly distinguished by the number of guns they carried. A "first-rate" like HMS Victory or the fictional HMS Defiant (wall painting in "In a Mirror, Darkly") would carry 104 guns, a second-rate 90-98 guns and a third-rate 64-80 guns.
All these ships had in common that they were "ships-of-the-line", i.e. they were considered powerful enough to engage the enemy fleet in the traditional parallel lining and broadside exchange (Nelson broke this rule and therefore won at Trafalgar in 1805)
Avro Arrow wrote:
Which is why I don't personally think that any ship referred to as a starship automatically means she's the same class as Enterprise. Sorry. YMMV, of course.
Enterprise's commissioning plaque notwithstanding, of course. Since that was there from the earliest days of the series, I think that's just one of the things that hadn't really been ironed out yet (like Earth vs. Federation ship), and at best refers to "Starship Class" the same way you might refer to a "destroyer class" vessel IRL, but then within the destroyer classification, you'd have, say, St. Laurent or Restigouche class ships.
Could this be a possible rationalization of starship vs. Starship Class? The Royal Navy had all kinds of ships in the 18th and 19th centuries; however, only a select few were "Ships of the Line." Those were special ships had their own distinction and, as Robert describes, different ratings.
So TOS has spaceships and starships; however, Starships as in the Starship Class are a distinct breed. They are the 23rd century equivalent of a Ship of the Line. There are only 12 like Enterprise in the fleet because they are so rare and special. Oh, sure, there are other space ships, but they are inferior when compared to the Starship Class.
Just tossing this out there as a possible rationalization.