Perhaps im just too naive about Trek, but ive never concretely understood why the Defiant series was never put into mass production like the Sovereigns and Excelsiors were. To my perception you could build at least 3 Defiant classes for one "heavy" cruiser model, and considering the types of bad guys the Federation's dealt with id argue they have plenty of "explorer" type vessels to work with.
We only ever saw one Sovereign-class onscreen in all of Trekdom. It would be fair to ask why it too, never caught on.
We know of at least six Defiant class vessels aside from the original. Valiant, Sau Paulo, the two visible in the fleet the Defiant and Martok's ship joins in the Season Five finale and the two that helped attack the Romulans and the experimental Starfleet ship on Voyager. Not bad for a ship that was apparently difficult to build and hard to work the kinks out of.
^ For all we know (lacking names or registry numbers) the two from Call To Arms and the two from Message In A Bottle could have been the same two. Also, there's what look like two more right at the very end of Endgame about 2 seconds before the credits roll. I too hope they produced a lot of the class. A lot of bang for their gold pressed latinum.
The fact that we never saw a fleet of Defiants in one spot doesn't necessarily mean that only a few were built. There is no need to send them all into one area of space, especially if older ships can be upgraded to similar weapons capacity (e.g. the Excelsior-class Lakota was armed with quantum torpedoes). Ships of the older classes would've been seen in greater numbers because many more had been built over the previous hundred years or so.
Absence of evidence is not evidence of absence. Just because we didn't see a lot of them doesn't mean they weren't out there. We didn't see or hear much to prove there were or were not lots of Defiant class ships around. You can fill in the blanks as you like.
On a related note, the Enterprise (no bloody A, B, C, D or E) was the only one of the Connies to have that refit we saw in TMP...
Had the Dominion Scarabs been more of a threat--I think Defiants would have been put into production--had the war lasted longer.
A wise person once said, "Space is big. Really big. You just won't believe how vastly, hugely, mindbogglingly big it is." With Starfleet deployed across several thousand light-years, some designs may be more visible than others depending on where you are. In some parts of the Galaxy, you may see many Ambassador-class ships still in service, while you may not see them at all in other regions. The same would hold true with most starship designs, IMO.
As has been pointed out, there really is no canon evidence as to the number of Defiant class ships in the fleet. There might be a handful, there might be hundreds, we just don't know. Personally, I would doubt that there are many, for the following reasons: 1) Although Star Fleet is tasked with defending the Federation, it is primarily for exploration. Most ships in the fleet seem capable of both tasks. A ship designed primarily for warfare is very much against this philosophy, and would not be approved in large numbers. 2) I concur that we have only seen a fraction of the fleet's actions during the Dominion war. However during DS9 we have seen some of the most significant battles of the conflict. Given the apparent effectiveness of the Defiant class, surely they would have been more use in the first and second battles of Chin'toka, or during Operation Return, than the hordes of clay-pigeon Mirandas and swarms of questionable value attack fighters? 3) The DS9 Technical Manual (a non canon source, I'll admit) states that only six were ever planned, and that construction of each ship required rare materials (non-replicable) with a long fabrication time. As I say, there is nothing concrete on this matter. But that's why I feel Defiants are few and far between.
The Badger makes some good points. I'd like to add another one, just for the helluvit. While Sisko's Defiant prototype proved to be an effective combat vessel to aid in the Federation's survival, the notion of mass-production of this class of ship raises unique security questions: The Defiant proved to have unusually good offensive capabilities, in addition to its defensive capacity. Even one of these ships, falling into the wrong hands, could prove to be an incredibly powerful weapon that could destabilize even major galactic powers. Witness the third-year DS9 adventure "Defiant". Given this, and given the thoughtful leadership of the Federation and Starfleet, one could easily surmise that the question of the Defiant-class warships' security simply had to come up. Even if there were some "security key" that could disable the ship's cloaking device and weapons (which Kira foollishly disabled when twin-Riker stole the ship), the Federation would have to consider the possibility that at least one of these warships would eventually fall into the wrong hands. The Federation would also have to consider the possibility of large numbers of Defiant-class warships eventually being mothballed in the event that the Dominion invaders would be defeated and the war ended. What then? If large numbers of Defiant-class warships had been produced, Starfleet would wind up with a large number of dunsels on its hands. So, what would the Federation do? Hollow-out an asteroid and store abandoned warships inside? Decommission most/all of these ships? (What if they were needed again to repel a Borg invasion?) And even if the Federation did mothball these little space-tanks inside "a great rock in space", Starfleet would have to protect and secure these crown jewels lest they be stolen or otherwise attacked while unmanned. To put it bluntly, would you want Roger Korby to have a chance to infiltrate Starfleet and get his hands on one of these bluejays? In some respects, the notion of the Defiant as a compact, uber-warship is "just what the doctor ordered" for security threats like the Dominion and the Borg. But the Defiant also signals the return to a WAR GAMES scenario, or maybe CRIMSON TIDE or TWILIGHT'S LAST GLEAMING. Given this, I think it's most likely that the Federation would maintain a small number of these warships, only producing an absolute minimum number to achieve military objectives. Beyond that, the security complications would quickly grow out of control.
I suppose it would depend in part on the overall composition in the fleet, and whether the serious losses the Federation suffered during the war would require more stop-gap efforts in the short term.
That's simple enough: The show runners wanted to save the ship for the movies. It was nothing more than that. The class was designed for the movies, so that's all we would ever get to see it in.
Well in terms of the Soverign Class we know of only two, the Soverign herself and the Enterprise. No evidence of mass production As for the Defaint Class we know of at least 5, Defiant, Valiant, Sau Paulo, and two unnamed ones in VOY "Message in a battle". So from onscreen evidence the Defiant has had a wider production run than the Soverign.
Cheers mate! This is indeed another valid point, one I hadn't considered. It does make sense. True enough, but that's an out of universe explanation. What I, and, I suspect, the OP, want is a credible in universe explanation. The Sovereign being a new design, not yet available in large numbers, is one possible explanation, though I'm sure others exist. It's possible that one of the two unnamed vessels seen in 'Message In A Bottle' was the Defiant herself, in which case there may have been as few as four.
I did consider that, but if it were why not have even a line a hailing frequency from an actor from DSN?
Unless the Defiant itself were in charge of the operation to recover the Prometheus, it wouldn't be their job to do any hailing. If the Akira class, or the second Defiant class, were in command, they'd be the ones doing any hailing. There's no real reason to send out a message, "Hello, just calling to let you know we're from Deep Space 9."