That assumption is based on the one line in the film that references it as the first Warp Four vessel. However, the first warp 4 vessel was an Emmette style ship which preceded the NX class entirely.
No, it wasn't.
I mean, it
could have been, until the movie told us it couldn't.
The registry number of the USS Franklin depicted in the film was NX-326. (Now, this a discrepancy in its own right as starting with Columbia, the numbers should have been different and starting with NCC; the NX-01 designation given to the Enterprise meant "Prototype" and NCC means Naval Construction Contract that is used on ship that are in Active Service.
This is demonstrably false, because clearly NX-01 was not United Earth Starfleet's first-ever ship. NX-01, if denoting experimental, should have gone to that unseen ship, with Archer's vessel getting something like NX-123 instead.
OTOH, Archer's ship was indicated to be UE Starfleet's first-ever deep space exploration ship. So the X there could well be taken to mean eXplorer, with -01 rightly going to the ship we saw.
And to all her sisters. Archer said in "Fortunate Son" that four of the ships were soon going to serve Earth, and identifed the four as "NX class" - which makes no sense if NX means experimental, but perfect sense if NX specifies an all-new ship category with all-new capabilities.
The NX-01 was pulled into service prematurely and in the series, they never assigned it a new NCC number.
'
In the series, NCC-preceded numbers didn't exist. No vessel had that particular code ahead of her registry number - indeed, no other ship had a registry number visible at all, save for sister ship NX-02.
The designation numbers move upward - meaning a larger number is a more recently built ship.
This sounds like a reasonable assumption. Given how Archer's ship was -01, we must then assume each separate ship category proceeds at its own pace through the numbers - possibly combat vessels were up to -891 in their particular sequence, tugs up to -327, and so forth.
The USS Franklin was NX-326
On a dedication plaque indicating that she belonged to the
United Federation of Planets Starfleet. The plaque thus must have been created long after the ship herself was created. And in the UFP Starfleet system, NX indeed appears to denote experimental rather than exploratory vessels. -326 may have been slapped to that old clunker when she ceased to be good for anything else but engine testing, then.
This was how things were done in the Earth Starfleet, ship classes had letters for their names and those letters were used in their registry codes. The Intrepid for example was NY class, its registry NY-05.
This isn't an onscreen fact at all.
The only thing that got a registry number besides the hero ship and her sister was the ECS freighter
Fortunate (ECS-2801 in an obscure computer readout, not painted on the hull); by implication, other such freighters probably had numbers as well, in-universe. Starfleet's own ships never got either letter codes or registry numbers.
-Was about 10 or 15 years old when the Federation was founded in 2161, so hardly a very old ship. Outdated perhaps, given the warp technology advances.
Since Krall's ranting in the movie suggests the thing called the Romulan War took place between the introduction of the ship and her assigning to Edison, we could well say the ship was thoroughly outdated: the four years of WWI and the six or so of WWII completely outdated the top-of-the-line designs from immediately before that war!
Note that NX-01 was also retired around that time, as per the ENT finale - quite possibly for similar reasons.
Since the registry doesn't make sense in the Earth Starfleet context (the Franklin isn't a NX-class ship like the Enterprise, and 326 is too high a number for a NX-class ship anyway), it's likely that the registry is a Federation Starfleet registry given in 2161 when the amalgamated fleet was formed. There were probably more than 300 ships in the common fleet and it would explain the UFP dedication plaque.
A modification of this model would have registries in the 300 range assigned to a specific kind of ship, registries in the 200 and 400 ranges to other sorts, and numbers up to 1200 being assigned, in a fleet that was about 250 ships strong overall...
OTOH, UPF space might well be cluttered with thousands of excess starships in the aftermath of the recent war...
Why the NX prefix standing for an experimental/pilot ship? Well Franklin was the first warp 4 ship, so likely the pilot ship of its class.
Or the only one pulled aside to act as an engine testbed back in her day, with all her sisters continuing to putter along at warp 2 in their designed role as insystem patrol cutters or outpost supply sloops or whatnot.
Or even the victim of not just one but two unfortunate warp engine malfunctions, the first forcing her warp 2 engines to warp 4, the second one throwing the ship all the way to Altamid.
What we do not know about the Franklin, and probably never will:
-Its Earth ship class and/or Federation class ("Starship-class" is rather meaningless).
Indeed. (Sometimes the fandom has gone by the names used in earlier script versions, though, and I think this baby used to be the
Pioneer there.)
-Its original Earth registry
Provided she had one. ECS might have been more bureaucratically minded than UESF!
-The year it was built and the year it disappeared (a few years after 2161?)
And the first one is further obscured by the totally unknown progress towards the warp 4 record. Early on in her career? Towards the twilight?
Timo Saloniemi