Build:Star Fleet Registry Numbers
2.1.10 Star Fleet Registry Numbers
The method in which the two incarnations of Star Fleet (that of the United Earth and of the United Federation of Planets) registers its ships has changed three times. The UESF, upon its formation, registered vessels numerically following the classification codes (ex: EC-19) in chronological order of the ships built in that classification code, as per the traditions of one of its preceding services, the United States Navy. That is, when a vessel was first commissioned into service, it assumed the next available hull number for that classification type (ex: heavy escorts). Generally, blocks of a classification code were assigned to specific class of ship within that type. Within the UESF’s period of time, ships generally didn’t see their type change (ex: heavy escort to escort), so there weren’t any conflicts with competing numbers within one type.
The UFP’s Star Fleet re-registered all vessels it inherited upon its formation and didn’t foresee that more than 100 vessels of any one class would be built. As such, the inherited and new-build vessels were all assigned a range of 100 numbers to fill, that was limited to that specific class. When a new class was built, it would receive the next block of 100 numbers. If a class exceeded 100 units built, it would be assigned another block of 100 numbers, often separated from the original block. This created gaps within the overall numbering sequence, appearing to suggest there were more starships within the Star Fleet than actually existed. (This was also an advantage for "black ops" ships, which could be assigned a number in a non-related class and sneak by extreme scrutiny of any watchdog or intelligence groups monitoring Star Fleet’s construction programs.)
Starting in the 24th century, it was decided to go with a less "managed" system. Instead, blocks of 1,000 numbers would be assigned to each calendar year, with ships being assigned their registry numbers as they were ordered. The numbering scheme didn’t clear the previously registered numbers from operational ships, but instead jumped to 11000, starting in the year 2301. (The thousand's digit usually indicates what year the vessel was intended to be commissioned, though this did not always hold true.)