Let's see. I've conquered the galaxy a number of times and with almost every major power however I believe my best single all out battle was as the klingons. I was playing as the Klingons and had killed every major power except the Federation. I had conquered every sector they had except the Edo, and their gardian. Since they were the last sector of the federation they would not except bribes so I had to go in a conquere the people. So I took 300 ships the best ones the Klingons have, I can not remeber their name or class, into the sector and took on the Guardian. It took over three minutes to load after I selected assault. It was over in a mater of seconds but of the 300 ships I came out with only 10. I had to built some more ships to take the sector but in the end they bowed before me and I had the galaxy to myself.

270 ships 300+ ships lol how ya do it? max i had going at once is around 190 romulan destroyers, i like skirmishes like sending a scout ship against an outpost and putting it on evade, 9 times out of 10 scout wins. i like to play as romulan, being extreamly isolationist i just keep myself to myself develope around 3 systems max and keep starbases over em, my fave trick is to ignore all the major powers, just make friends and trade with minors, when im sufficialy advanced to develope destroyers quick i begin to develope them in 9's and send them to romulas for training or send them against the edo guardian echo papa or any random bad guys like the borg chodak etc and get em some xp, if i tend to stay in my system and dont stray out the other major powers tend to leave you alone while they slug it out, granted they may all declare war on you but exept for the random ship's nothing realy happens... anyway one such battle a few days ago occured in a large galaxy, me as the romulans, in the course of the game id uncovered the map and strategicaly planted starbases here and there so i pretty much watched every empire declare war against each other, i realy HATE the cardies so i periodicaly send raiding groups into cardassian space to destroy starbases and colony ships n such, so they were the first to fall to the ferengi, meanwhile id refused war pacts with the federation and klingons they had been pretty much slogging it out for the past 70 turns, the federation was losing bad, eventualy the federation fell and the klingon empire was victorious. it then turned its eyes toward me and the ferengi, id previously signed a friendship treaty with the ferengi so id been left in peace happily training my ships crews, the klingons declared war against the ferengi.... by now id been offered an alliance to wich i agreed then 2 turns later i got a war pact to which i also agreed ... i then commenced to do absolute nothing just watched the klingons and ferengi play they're intergalactic pong match, to put it bluntly the klingons anihilated the ferengi the ferengi home worlds were lost, reduced to just a few piddling planets the klingons decided to destroy, now the klingons had pretty much sunk everything into this war so i wasnt worried about splitting my huge fleet, especialy as my funds were at a rock bottom, i sent a fleet of 100 ships into the heart of klingon territory and whiped out its home systems in 5 or 6 rounds, the same with the federation and cardassian conquered systems. eventualy the klingons defeated the ferengis then came against me .. with all its remaining 30 ships, id had my inteligence on sabotage and stole around 10 klingon ships giving me a total of 100 ships in romulan space, i would have like to watch the battle but my machine would have crashed, i lost an equal ammount of ships but id defeated the klingon fleet leaving me free to split all my ships up and mop up the remainder of the klingon empire... i spose it must have been a good day to die

Recently i played a building mod game halved the upkeep cost for all ships and stations to get some large battles. Also edited some of the systems to get larger production capacities for all majors. ie the Romulans had a system with nearly 900 pop, Fed had several above 600.
I played the Cardassians growing to a small empire quite quickly with 2 minors and stopped expanding. I got friendship treaties with Feds and Romulans to my south and hadnt made contact with Klingons and Ferengi. Soon the Feds declared war on the Roms which were at that point realy small compared to the Feds who had already assimilated most minors in their part of space (6 or 7). They almost anihalated the Romulans instantly only leaving bits for me when I declared war on both of them so I could get to Romulus before the Feds would take it. The task force I used consisted of 27 Galor cruisers (which are not the comand ships in Buildingmod) and 36 of the smaller cruisers. I took the beaten down Romulans with ease but was ambushed by about 200 Federation Ships in the 900 pop Romulan system next to Romulus. The Fed Fleet was comprised of about 100 Ambassadors (better than my lighter cruisers but a bit inferior to my Galors) 60 Mirandas 20 - 30 Galaxies and a hand full of Nebulas. Beeing outnumbered 4:1 tried to make a stand while they attacked my local Starbase (SB and Outposts are about 10-15 times stronger than in normal game). I had no chance and retreated my fleet after my Starbase was destroyed and my fleet had taken serious casulties (20% destroyed 30% damaged).

I already had dispatched most of the rest of my fleet to the former Romulan space (around 60 Galors and an equal number of light Cruisers). Meeting at the border to now Federation space I assembled a fleet of about 150 ships. With the casulties I inflicted on the Feds the last time they still had a slight superiority in ship numbers but were inferior in overall firepower. In the end I totally anihalated the whole Fed fleet but in return also lost about 30% of my ships.