For those of you who may be interested this is an updated version of a post I made sometime ago. It is provided as FYI, and in no way is intended to imply that this is the proper explanation of their use in Star Trek. I have been a student of naval history for sometime, and provide this for your use as you deem fit.
Topic #1 : USS
All navies of the world have some form of this. In America we use “USS”, standing for United States Ship. Britain uses “HMS”, standing for His/Her Majesties Ship.
This comes from the need to identify the nationality of a ship. It is abbreviated because “United States Ship Iowa” is a mouthful to say.
In Star Trek I have seen two options: (1) United Space Ship; and (2) United Star Ship.
Topic #2 : NCC and NX
In all navies before a ship can be built a contract has to be signed. This contract has two parts: it proves the intent of the government concerned to actually pay for the ship [the contract]; and it approves the ship as being seaworthy after its completion [the certificate]. Thus it is called the Naval Contract Certificate [NCC].
Before a ship is ever named it is given an “NCC” number for identification; the ship being named much latter. In most navies the “NCC” number is painted on the bow of the ship (w/out the “NCC” letters) for identification. [The actual name of the ship being painted on the ships stern.]
All ships of the same class are given concurrent “NCC” numbers. For example, of the four Iowa-class battleships built by the U.S. Navy, they are: USS Iowa, BB-61; USS New Jersey, BB-62; USS Missouri, BB-63; and the USS Wisconsin, BB-64.
The “NX” designation has no existence in naval history. New ship designs are given an “NCC” number ass any other ship. The letter “X” does typically designate, however, an experiment; so Naval eXperiment could be one explanation.
Topic #3 : Commodores and Fleet Captains
A commodore, in the British Navy, is captain commanding a squadron or a division of a fleet. The title was temporary and the grade was not recognized. When a commodore had on his flagship a captain under him, he received the pay and allowances of a Rear Admiral.
Prior to 1862 the rank did not exist in the U.S. navy, but the title was given by courtesy to a captain who had command of a squadron. The rank and grade were abolished in 1899 (except as a title by which captains with Civil War Service were retired), being brought back for use in both world wars; and still being used today [being termed, however, Rear Admiral Lower Half].
Fleet Captain formerly, in both the British and Austro-Hungarian Navies, was used to distinguish between those officers who held rank of captain and commanded a ship [captain]; and those who held the rank of captain and served as chief of staff to a flag officer [fleet captain]. It was not a rank, but a title.
The title Fleet Captain had a corespondent in the title “Fleet Engineer,” the person responsible for inspection of and advising the flag officer in regard to engineering questions with consern to a squadron or division of a fleet.
Topic #4 : Fleet Admiral
From Britain comes this naval tradition. The rank of Admiral (4 star) is given to those persons commanding a bureau, naval base or station, or combination of fleets. A Fleet Admiral (5 star) is given to those who are a member of the “Admiralty Staff.” At any given time there are four Fleet Admirals [also called Sea Lords). The head of the Admiralty is a politician, called the First Lord of the Admiralty.
The only time in U.S. history that Fleet Admirals were appointed was in World War Two. This was done so that on the joint naval committee of the UK/US the U.S. admirals would not be junior to the UK admirals. The rank fell into disuse after the war.
In the English speaking nations the term Fleet Admiral is preferred. In nations such as Germany and Russia the term Grand Admiral is used. The terms are interchangeable—meaning the same thing, and is the corespondent of the land forces rank of Field Marshal.
Topic #5 : Ship Class and Type Class
As we all know the ships class is named after the first vessel of that class. In addition, in every navy, a ship is given a type class to label the ships primary duty/function. The following are the major ship profile types:
Aircraft Carrier (CV); Battleship (BB and DN [old style]); Heavy Cruiser (CA); Light Cruiser (CL); Destroyer (DD); Frigate (FF and DL [old style]); Submarine (SS); Hospital Ship (AH); Oil Tanker (AO); Transport (AP); Cargo Ship (AK); Repair Ship (AR); and Salvage Ship (ARS). [The “A” signifies that the vessel is an auxiliary ship, and not a ship of the line.]
When a ship undergoes an up-grade a change is made in its type class, NOT its ship class. For example our game is on a Miranda -class Light Cruiser (F-CL). The Miranda -class has no rear firing phaser banks. Ours was given an up-grade to add one aft ventral; making it a Miranda -class Light Cruiser (F-CL+).
Anytime another ship, of any class, is given rear firing phaser banks (called a plus-refit) it will have a “+” added to its type profile. For example the pre-movie Enterprise given the plus-refit would be a Constitution -class Heavy Cruiser (F-CA+). The movie Enterprise however would only be a Heavy Cruiser (F-CA); without the “+” because the plus-refit was built into the class.
The name given the refit is determined by naval engineering command. It could easily have been termed the r-refit (F-CLr), or anything else you can think of. Once named, however, it remains with that name; making it easy to tell what the additions to the type profile mean. [You can thank our chief engineer for our refit name.)
When a vessel undergoes a re-fit (such as Enterprise did for ST:TMP) the hull and systems are so modified that it is considered a new class; to be named after the first vessel of the class. Thus the reason that some [such as myself] refer to the movie Enterprise as an Enterprise -class Heavy Cruiser.
When asked to identify itself a vessel should give name/class/type/and NCC number. For esample: “USS Iowa; Iowa-class; BB-61.” Thus you know that it is a United States Ship named Iowa (61) and is a battleship of the Iowa -class. [The pre-movie Enterprise, by current naval standards, would identify as: “USS Enterprise; Constitution-class; CA-1701.”]