why do starfleet have just one redister code for its starships*? seriously, just NCC indipendently by ship functions? In real world ships have different register for different purpose, and the register code have a meaning: e.g.: FPSO : Floating Production, Storage and Offloading Vessel LNG/C: Liquefied Natural Gas Carrier RMS: Royal Mail Ship SS: Steam Ship TSS: Turbine Steam Ship etc... So, why all federation ship have the same register code, and what does it mean? *NX doesn't matter
I don't expect anyone can answer this except through sheer speculation. But, for US navy submarines, the designation is, in part at least, based on propulsion. Since Trek ships are all warp starships, that distinction doesn't exist, for instance.
How about NAR? It shows up a few times. A lot of the background, unseen ships we see on computer displays in TNG also had different registry code prefixes. http://en.memory-alpha.org/wiki/SS_Vico
As has been mentioned already we have seen other registries other than NCC, NAR, NCV (USS Relativity). Besides we tend to see starfleet vessels and NCC might be reserved for starfleet vessels, whilst non starfleet vessels carry a different letter designation.
According to http://en.memory-alpha.org/wiki/Registry , NCC seems to only be for core Starfleet vessels, other registries are used for other purposes. However between 2161 and 2380 ish, there seem to have been 80,000 NCC registries, which would allow for the addition of just under 400 new NCC's per year (average). Given that many starships probably serve for many years - for example Mirandas, Excelsiors, and Oberths, this would not seem an unreasonable number. Even if every ship directly owned by the Federation (as opposed to non Starfleet ships owned by member race governments) had an NCC reg, it shouldn't be too much of a number-crunching problem to keep track of them, even if they are not sorted. For example in RL, look at the way USA registered aircraft are registered, N-xxxx, irrespective of type. USAF aircraft seem to be numbered by a year prefix, then a sequential issue number. Some grouping by type may occur if a batch of vessels are ordered at one time, for example the NCC-17xx series, but it would seem that, with the exception of legacy registries, eg NCC-1701 and possibly NCC-1305, the reg is simply an accounting tool. I wonder if the Federation would keep NCC-01 as a legacy number also, perhaps as an equivalent of 'Air Force One'. ?
To me, it sounds like "NCC" is only used for Federation Starfleet ships, not necessarily Federation privately-owned ships, Federation civilian government ships, or Federation Member State ships.
Or they figured using different designations for different classes or purposes would confuse the fans.
The question though is why should the Federation Starfleet conform to any current system in use today by today's Navies?