There's also the Class 6 supply ship Lantree
. Adding this to FJ's ideas on the hero ship and certain others being Class 1 sounds logical enough: the lower the number, the more important frontline role the ship type plays - or, more broadly, the more qualified it is to play an important frontline role. Perhaps something like Class 4 or Class 6 gets pressed to military service in times of great need, even if it normally is a civilian or retired category?
We know what a Class F shuttlecraft looks like. We've no idea what a Class E or A or L looks like.
We know what one
Class F shuttlecraft looks like. There might be dozens or hundreds of different designs meeting those criteria. After all, "Class F" is the first, arguably most generic thing the computer is able to establish about the target it is asked to scan; narrowing down might allow it to eventually deduce that it is of the M-47 Widowmaker
type rather than the H-227 Beater
model with the triangular hull and three nacelles but with similar performance appropriate for Class F.
The same would apply to Class J. Perhaps both the Mayweathers' old transport and Mudd's completely different-looking craft fit the parameters somehow?
There is also of course the possibility that Class F and Class J are actual "proper" class names, in the spirit of the Royal Navy's R-class battleships: there is no USS J
, but there is a general theme of all the ship names beginning with the letter J. We never heard the name of any Class J ship in TOS, after all.
Of course, in ENT one J-Class vessel had the proper name Horizon
, and one Y-Class ship was the Fortunate
. The concept of Class J might be a Starfleet one, and the name in turn something the users later gave to the vessel after acquiring it from Starfleet surplus... But I rather doubt the Boomers would have referred to their home by Starfleet terminology, and we never really heard hints of such a backstory, either. Best, perhaps, to accept that civilian ship designations from before the founding of the Federation should not be expected to be in line with 23rd century Starfleet parlance.
On a general note, civilian ship classes seldom follow the concept of being named after the inaugural ship. Designations like "DY-100 class" are quite likely to be found there, in the world of multiple operators, constant sales forward, customized orders and so forth. And the industries selling to various militaries in turn have their own designation schemes, so various navies might purchase ships designated MEKO-100 or MEKO-350 - but would never refer to their vessels by this designation again after they were handed over and integrated to the fleet.