Registry Number

Every ship in Starfleet has a registry number which is used to identify it in computer records and the like. Most such numbers begin with the prefix NCC, which stands for Naval Commission Contract. In other words, a ship's registry number derives from the number assigned to the paperwork which authorized its construction. Experimental or prototype vessels may instead have the prefix NX (Naval Experimental). Civilian vessels use a plethora of designations.

A ship's registry often indicates the approximate timeframe during which it was built and commissioned (see accompanying table). Due to the vagaries of the Starfleet bureaucracy, snags in the contracting and construction process, ships named to honor earlier ships, and other factors, a number may be assigned (or re-assigned) which, to outside observers, seems to contradict this system. A proper search of the relevant Starfleet records will always unearth the precise information about when a ship or its class was constructed.

Starfleet Registry Table

Number Series	Construction Timeframe
3- or 4-digit numbers	Prior to 2310
10000 series	2310s, 2320s
20000 series	2320s, 2330s, 2340s
30000 series	2320s, 2330s, 2340s
40000 series	2320s, 2330s, 2340s
50000 series	2340s, 2350s, 2360s, 2370s
60000 series	2350s, 2360s, 2370s
70000 series	2350s, 2360s, 2370s

Registry Code	Ship Type
NAR	A Federation civilian research vessel
NCC	A Federation Starfleet vessel in active service
NDT	A Federation civilian transport vessel
NFT	A Federation civilian transport vessel
NGL	A Federation civilian freighter or cargo carrier
NSP	A Federation civilian science vessel
NX	An experimental Federation Starfleet vessel

Source

Spacedock: The Advanced Starship and Construction Manual Netbook, published by Last Unicorn Games, p. 16