Different ship classes may simply be the result of different design bureaus and build programs. Maybe it's politically easier to get approval for a new and different class of ship through the Federation Council than it is to authorize the construction of more ships of an existing class?
I think because the condition of the Federation force them to do that. Remember that there are many adversaries in the galaxy that surpass the Federation in both of technology and military power. Thus the Federation needs to develop their Space Navy more and more. And because of the rapid expansion and development of the new technologies (to chase and to reach the Borg technological level) they need to build new ship classes again and again. Don't use USN as the benchmark / example for the situation of Starfleet, as USN is stay on the highest tier in naval capability on Earth this day. That's why they don't need too many classes to fulfill the role in their rank. Just look at the fleet. There are only a few type of capable USN warships out there. From the old Oliver Hazard Perry, Ticonderoga Class, to Areligh Burge flight 1 and Flight 2A, and 2 Littoral combat Ships classes (and later Sumwalt and Burge III - I use Cruiser, destroyer and frigate and avoid other classes like carrier and LHD etc). Because they are the leader of the world Navy, they don't need to many ship class to fulfill the navy need. Yet, it is different to China, where is in rapid development and expansion of their navy capability. There are many ship classes type that overlap one to another. Ranged from 051, then 051A, 051B, and 051C, then they have 052, 052A, 052B, 052C, 052D, they have also Russia's Sovr (I forgot how to write it), with Frigates like 054, 054A, 053 with their many variations) and later they will develop 055 Destroyer / Cruiser, and the next gen frigate 054B. Remember, in China, the class 052B and 052C are entirely two different ship classes and have different roles, although both use 052 type hulls and their designation are destroyer. Not only that, they have even have a lot of submarines classes (Kilo, Improved Kilo, Song, Ming, Yuan, Han, Sui etc) compared to the USN's Los Angeles, Virginia, Ohio, and Seawolf. So I think the state of Starfleet is the same as China in modern day. They expand, they develop, they improve, but they are not satisfied (yet) to their current level of capability, because they use Borg (and later Dominion) as the benchmark of their development project. Look at what happen to the new toys that developed by the Fed since the incoming of Borg in TNG. Steamrunner, Defiant, Akira, etc. None of them are capable to match a single borg cube (Star Trek First Contact). So that's why they still developing and build more new ship class. Who know, one of them will capable to match a borg cube. But I think that rapid / crazy development will be slowed down after the event of Star Trek Voyager. The new techs and weapons that brought by the Voyager give the Federation more than enough weapon to stand toe on toe against anyone in the milky way galaxy. IF our Star Trek Writers know about military logic a bit, the new Luna Class should be a new Starship that capable to equip and exploit the new found technology from Voyager, and thus will become their new Ace against the next borg onslought.
You all gave great answers. I'll give my mediocre suggestion. Is it possible that the diversity of ship designs with very little uniqueness to offer comes from input of the non-humans in the UFP? Like the Norway class is the Vulcan answer to Intrepid? Akira is the Andorian answer to Defiant? Something like that?
Well, several of the FASA classes (Andor, Loknar and Thufir - missile cruiser, frigate and destroyer respectively) were mentioned as having been primarily designed by Andorian interests and the Loknars even seemed to have a number of crews who were exclusively Andorian. But it's not clear exactly what defined their "Andorian" traits otherwise since their designs are largely consistent with basic UFP principles. One could argue that the Andorians, having a racial inclination towards violence to some degree, found a natural home in Starfleet as military officers and would likely be supportive of designing warships to deal with enemies like the Klingons and the Romulans.
That's pretty cool. I never knew that. Kind of explains what the non-humans in the UFP get to contribute to ship design. :P
I'm not sure where you get the idea that having a lot of ship classes is particularly unrealistic. This is particularly true when ship designs have extremely long designed hull lives and an ability to be refitted with modern technology regularly. If we go with modern hull designs where you have a relatively small number of capital ships, I suppose having a handful of modular ship classes that you can mass produce makes sense, but when you consider the sheer number of shipyards, potential designers and mission capabilities required by Starfleet, you're probably looking at a model more similar to the Royal Navy of the 19th century where you had ship "rates" that fell into general capabilities, but then design classes that were dependent on who the Surveyors of the Navy (designers) were, which civilian yards were getting contracts, who was in power at the Admiralty, etc. For example between 1780 and 1830 there were at least 25 distinct classes of 74-gun third rate ships of the line designed in England, with many of these ships serving for the duration of the French Revolutionary and Napoleonic Wars. (1791 - 1815 so far as the RN was concerned) This isn't counting of course the various captures that the RN had gotten from the French, Spanish and other navies, which would add another 5-10 distinct classes just for battleships alone. Add everything from luggers to cutters, sloops and frigates, and you have well over 100 classes of vessel being used by the first truly global power.
As I said in my previous post, there really isn't any rhyme or reason, it's just the nature of "us", and shows up in reality and fantasy. Just compare it to the Automotive Industry, everybody thinks their version is better than another, and many people agree given the sales numbers. A term for it/that is "competition". There's no reason for this element to be excluded from Fantasy.
Does this include submarines and surface ships? To be a true comparison, you'd need to pick one or the other. Just curious.
I don't know why you'd have to pick between surface ships and subs. The totality of the US Navy is what makes it an important sea-going force. But let's use the other example: RN circa 1812-1815. I'm going to go with rated ships and cruisers (sloops) for brevity's sake. An appropriate comparison class will be included alongside for what Starfleet's "equivalent" would be. Royal Navy ship classes roughly circa 1814 Ships of the Line First Rates "Modern" First-rate classes Caledonia-class (120 guns) - Launched 1808 - 1 ship (later includes 3 additional ships after 1820) Ville de Paris-class (110 guns) - Launched 1795 - 1 ship Hibernia-class (110 guns) - Launched 1805 - 1 ship Ocean-class (110 guns) - Launched 1805 -1 ship Impregnable-class (100 guns) - Launched 1810 - 1 ship (2 additional built to lengthened design) Additionally captured ships are: San Josef (110 guns) - Launched 1783 by the Spanish Total Classes in Service: 5 Average Class Age as of 1814: 8 years 2380s Starfleet equivalents: Vesta, Sovereign and Galaxy-class starships. Pre-1790 first rates: Victory-class (100 guns) - Launched 1765 - 1 ship Royal Sovereign-class (100 guns) - Launched 1785 - 1 ship Royal George-class (100 guns) - Launched 1790 - 3 ships built, 2 surviving as of 1814. Total Classes in Service: 3 Average Class Age of 1814: 34 years Comparable Starfleet design as of 2380s: Ambassador-class. Second Rates 3-Decker Second Rates (Older first-rates and designs built to similar draughts, but somewhat smaller. Less sea-worthy but "tougher" in a fire-fight) Barfleur-class (90 guns) - Launched 1768 - 4 ships built, 2 ships surviving as of 1814 Duke-class (98 guns) - Launched 1777 - 4 ships built, 3 ships surviving Repeat London-class (98 guns) - Launched 1788 (original design 1766) - 4 ships built, 3 surviving Boyne-class (98 guns) - Launched 1790 - 2 ships built, 1 surviving Neptune-class (98 guns) - Launched 1797 - 3 ships built Boyne(II)-class (98 guns — Built to Draught of Victory) - Launched 1810 - 2 ships built Total Classes in Service: 6 Average Class Age: 35 years (counting the second Boyne class design as being similar in age to Victory) Comparable Starfleet design as of 2380s: Ambassador-class, possibly Nebula-class Third Rate Ships of the Line 80-gun ships (Quasi-Second Rates) Caesar-class (80 guns) - Launched 1793 - 1 ship. Additional ships of the type include: Ca Ira La Tigre Canopus Tonnant Spartiate Malta Brave Alexandre French ships captured between 1795 - 1806 Total: 9 Ships 2380s Starfleet Equivalent: Akira-class Starship 74-gun Ship of the Line (Mainline ship of the line) Pre-War Designs Bellona/Arrogant-class - Launched 1761 - 17 ships built, 9 ships remaining in service (2 as Razee frigates of 58 guns) Canada-class - Launched 1765 - 4 built, 2 remaining (1 Majestic as a 58 gun razee frigate) Albion-class - Launched 1763 - 5 built 3 in service. Ramilles-class - Launched 1763 - 9 built, 1 in service Royal Oak-class - Launched 1769 - 6 built, 5 in service Elizabeth-class - Launched 1769 - 8 built, 1 in service Culloden-class - Launched 1776 - 8 built, 4 in service Alfred-class - Launched 1778 - 4 built, 4 in service Ganges-class - Launched 1782 - 6 built, 5 in service (last unit of this class built in 1816) Carnatic-class - Launched 1790 - 4 built, 2 in service Total Classes: 11 Average class age: 43 years Starfleet comparison class: Excelsior-class, possibly New Orleans, Niagra classes as well as unseen classes like Ho'ukula "War" era 74s Brunswick-class - Launched 1790 - Ship Mars-class - Launched 1794 - 2 Ships Courageux-class - Launched 1800 - 1 Ship Platangenet-class - Launched 1801 - 1 Ship Ajax-class - Launched 1798 - 2 Ships Conqueror-class - Launched 1801 - 1 Ship Dragon-class - Launched 1798 - 1 Ship Northumberland-class - Launched 1798 - 2 Ships Spencer-class - Launched 1800 - 1 Ship Achille-class - Launched 1798 - 2 Ships Revenge-class - Launched 1806 - 1 Ship Milford-class - Launched 1806 - 1 Ship Fame-class - Launched 1802 - 9 Ships, 8 Remaining Vengeur-class - Launched 1810 - 26 ships built by 1814, 40 ships built in total through 1822. Total Classes: 14 Average Class Age: 14 years Starfleet Comparison: Akira, Nebula, Steamrunner. Few Fourth Rate ships were in commission during this period. A handful of 50 gun ships. One might liken them to the small number of Constellation-class ships still in service. Useful in limited circumstances to remain in commission. Frigates The work horses of the fleet. Many many different types by this period, including "super" frigates which were armed with large armaments of 24-pounders rather than the standard 18-pounder armament. "Super" Frigates Endymion-class, Launched 1797 - 6 Ships Built Acasta-class, Launched 1798 - 1 Ship Built Cambrian-class, Launched 1797 - 1 Ship Built Leander-class, Launched 1813 - 1 Ship Built Newcastle-class, Launched 1813 - 1 Ship Built Total Classes: 4 Average Age: 10 years Starfleet Comparable class: Prometheus-class, Defiant-class. (Combat centric, fixed purpose ships) Fifth Rate 18-pounder Frigates Flora-class, Launched 1780 - 4 Ships Built Minerva-class, Launched 1780 - 4 Ships Built Latona-class, Launched 1781 - 1 Ship Built Perseverance-class, Launched 1783 (repeat class built in 1800s) - 11 Ships Built, Remaining Pallas-class, Launched 1794 - 3 Ships Built Artois-class, Launched 1794 - 9 Ships Built Alcmene-class, Launched 1794 - 4 Ships Built Phoebe-class, Launched 1795 - 4 Ships Built Amazon-class, Launched 1796 - 6 Ships Built Penelope-class, Launched 1798 - 3 Ships Built Leda-class, Launched - 47 oak ships plus 8 of fir built from 1805 - 1932 Narcissus-class, Launched 1801 - 3 Ships Built Amphion-class, Launched 1798 - 5 Ships Built Lively-class, Launched 1804 - 16 Ships Built Apollo-class, Launched 1799 - 27 oak Ships Built + 10 from pine Total Classes: 15 Average Age: Starfleet Comparison: Intrepid, Luna-class starships. Fifth Rates below 18-pounders Examples here are: Southampton, Richmond, Amazon, Circe and Maidstone classes. Most were about 30 years old by the 1810s. Starfleet Comparison: Cheyenne, New Orleans, Springfield, Centaur, Norway-class. Sixth Rate Frigates/Post Ships (By this point these ships are badly outclassed, as they're still regarded as "frigates" but are usually outgunned by a comparable sloop of the American or French navies) Example classes of "Jackass" frigates: Enterprise, Mermaid, Banterer, Laurel, Hermes, Cyrus, Coventry, Lowestaffe Anywhere from 5-25 in commission during this time. Average Class Age - 6th Rate Frigates: 30 years, Post Ships: 5-10 years. Starfleet Comparison: Miranda, did I mention Miranda? Sloops/Corvettes Examples here are: Ship-sloops: Pylades, Cormorant, Bittern, Merlin. Brig-sloops: Albatross, Cruizer, Cherokee, Crocus Adding up to some 400 total vessels of something like 15 classes. Starfleet Comparisons: Nova, Oberth, Sabre, Merian-classes. (The Merians would act as "modern" replacements for Mirandas, similar in capability, but classed as something smaller) So in total we have something like 95+ classes, and these are not including things like coastal luggers, bomb ships, transports, and the like. Note also the average age.
Side note quibble: Given to that some extent Star Trek was envisioned as "Hornblower in space", I think some of these comparisons are probably more apt than say comparing to modern naval units.