Battle of the Omarion Nebula The Battle of the Omarion Nebula was the first major armed engagement between forces of the Alpha Quadrant and the Dominion , as well as the only large - scale conflict to take place in the Gamma Quadrant . Acting on a plan originating with Enabran Tain , a combined fleet of twenty Cardassian and Romulan warship s under the control of the Obsidian Order and the Tal Shiar launched a preemptive strike on the in the Omarion Nebula . However , the effort had long been infiltrated by a , and shortly after attacking , the fleet was ambush ed and destroyed by the Jem ' Hadar , with few survivors . Background . The year 2371 was an anxious time for the powers of the Alpha Quadrant , as the threat posed by the Dominion on the far side of the Bajoran wormhole began to grow . The Jem ' Hadar attacks in 2370 , claiming the Bajoran colony of New Bajor and the Starfleet ship , and a subsequent engagement between the and several Jem ' Hadar fighter s , revealed a ruthless , powerful empire determined to impose their version of order upon a chaotic galaxy . Although a full - scale invasion did not follow the initial first contact of the Jem ' Hadar as was initially feared , war seemed to be inevitable . ( ) Immediately , the Alpha Quadrant powers began to prepare for invasion . The United Federation of Planets assigned the " Defiant " to Deep Space 9 at the mouth of the wormhole to bolster its defensive capabilities . The Federation shared all of its intelligence with the Romulan Star Empire as per their treaty to allow a Romulan cloaking device to be installed on the " Defiant " . The Cardassian Union , occupied by its own internal and external concerns , remained relatively uninvolved . ( ) Secret alliance . At the time , ex - head of the Obsidian Order , Enabran Tain , was living out his retirement on Arawath . Frustrated by what he perceived to be the Central Command ' s complacency in the face of the Dominion threat , Tain drafted a risky venture to destroy the Dominion in a single decisive move ; by wiping out the Founder s . To accomplish this end , he enlisted the aid of the Romulan Tal Shiar , proposing a joint military venture into the Gamma Quadrant executed independently of either organization ' s parent government . However , unbeknownst to him , his opposite number in the Tal Shiar , Colonel Lovok , had been replaced by a Changeling infiltrator . The Dominion saw in Tain ' s plan a golden opportunity to destroy the two most effective security agencies in the Alpha Quadrant , and did everything they could to carry it forward . Through the Romulans , Tain had access to all the intelligence gathered by Starfleet on the Dominion . He reasoned , that as the Founders controlled the supply of ketracel - white , by eliminating the Founders , the Jem ' Hadar would soon die , crippling the Dominion ' s capability to wage war indefinitely . In great secrecy , the Obsidian Order began assembling a fleet of fifteen cruiser s in the Orias system , although Cardassian law specifically forbade the Order from operating military spacecraft of any kind . The fleet was detected by forces of Central Command during an incident involving the " Defiant " and the Maquis , but the buildup continued unabated . The fleet had been equipped with cloaking devices provided by the Tal Shiar , which had been modified to avoid detection by Dominion sensor s , provided they did not exceed warp 6 . Meanwhile , the Tal Shiar assembled its own force of five warbird s . Both fleets were manned by combat veteran s , and carried enough firepower to destroy the Founders ' homeworld down to its mantle within five hours . As part of the joint venture , the Tal Shiar carried out the assassination s of several former Obsidian Order operative s possessing sensitive information about Tain , including an unsuccessful attempt on Elim Garak . Aside from those involved in the operation , the only individuals who knew of Tain ' s plan were Garak and Odo , who had been captured by the Tal Shiar after investigating the deaths of the aforementioned operatives . ( ) Launch . In late 2371 , the combined fleet entered Bajoran space and passed through the Bajoran wormhole . As they did so , the fleet decloaked and transmitted parallel messages to their respective governments . In Tain ' s message to the Central Command , he outlined his motives , intentions and advised the Cardassian military to be mobilized for potential Dominion reprisals . Both the Cardassian Central Command and the Romulan Senate denied any prior knowledge of the mission , and denounced it as a rogue operation . Despite the possibility of war , they elected to wait and see whether or not the joint operation would succeed . Starfleet chose not to interfere with the strike , also deliberating whether to allow Tain a chance to succeed or not . Vice Admiral Toddman ordered a civilian evacuation of Deep Space 9 and dispatched a task force of nine starships to aid in the defense of the Bajoran sector . Against orders to commit the " Defiant " to the defense of Bajor , Commander Benjamin Sisko took the ship into the Gamma Quadrant , in the hopes of rescuing station Security Chief Odo . ( ) Jem ' Hadar ambush . As the fleet decloaked in orbit of the Founders ' homeworld , they found the planet apparently completely undefended , with the Changelings themselves in a liquid state on the surface . Confident of victory , Tain ordered the fleet to attack , instructing ; " " So much for the Dominion . Open fire ! " " Thirty percent of the planet ' s crust was destroyed in the fleet ' s opening volley . However , the fleet ' s sensors soon discovered an anomalous reading ; there was no change in the number of lifeform readings on the surface . Garak soon realized the Founders had already evacuated the planet , leaving behind an automated transponder to send out false sensor readings . Moments later , a massive fleet of 150 Jem ' Hadar fighters emerged from the Omarion Nebula , cutting off Tain ' s fleet entirely . The Jem ' Hadar ' s phased polaron weaponry easily breached the shields of the Cardassian and Romulan warships , inflicting severe damage and heavy casualties in a matter of minutes . As the fleet was destroyed piecemeal , Lovok revealed himself as a Changeling to Odo and Garak , aiding their escape , unwilling to allow a fellow Changeling to die . Overwhelmed at being outwitted by the Dominion , Tain chose to remain on the bridge of the doomed flagship , remarking " " these Founders , Elim , they ' re very good . Next time we should be more careful " " . Odo and Garak fled the crippled warbird in the runabout , immediately being set upon by Jem ' Hadar fighters . On the verge of destruction itself , the runabout was spared by the timely arrival of the " Defiant " , destroying the runabout ' s pursuers and rescuing the craft ' s occupants . Hopelessly outgunned and with no hope of retreat , what remained of the Cardassian - Romulan fleet fought to the death . Meanwhile , the " Defiant " fought its way out of the battle zone , managing to escape back to Deep Space 9 . ( ) A few members of the fleet , including Tain himself , survived the battle and were detained at Internment Camp 371 . The Romulan prisoners were rescued two years later by Garak and Lieutenant Commander Worf . Cardassian prisoners from the battle were released when the Cardassian Union formally allied with the Dominion . ( ) Aftermath . The short and long - term consequences of the battle could not be overstated . In any strategic and tactical measure , the Battle of the Omarion Nebula was a catastrophic defeat for the Romulan and Cardassian forces , and proved to have enormous ramifications for the powers of the Alpha Quadrant . The Tal Shiar was badly weakened , while the Obsidian Order was wiped out altogether . The power vacuum left behind by the destruction of the Obsidian Order led to the Cardassian Underground gaining momentum . Eventually , a " coup " overthrew the Central Command , restoring political control to the civilian Detapa Council . The Dominion exploited this development . Specifically , General Martok of the Klingon Defense Force was captured and replaced by a Changeling . The Changeling manipulated sentiment in the Klingon High Council into believing the " coup " on Cardassia had been engineered by the Dominion . This convinced Chancellor Gowron into launching a preemptive strike , triggering the bloody Klingon - Cardassian War . Federation refusal to support their Klingon allies , and further manipulation by Martok , led to the First Battle of Deep Space 9 , and eventually the . The Federation suffered significant losses in this war and the Battle of Sector 001 , while the Klingon Defense Force suffered heavy casualties in fighting both the Federation and the Cardassians . The Cardassian Union ' s infrastructure was crippled by the Klingons , as well as continued conflict with the Maquis . This , coupled with political problems within the Cardassian Empire , prompted Gul Dukat to enter into secret negotiations with the Dominion . Acting as the empire ' s representative , Dukat negotiated Cardassia ' s entry in the Dominion and Dukat was named the new leader of Cardassia in 2373 . ( ) Appendices . Background information . When the staff writers of came up with the idea that third season installment would establish a military buildup which the Obsidian Order was involved in and which was so mysterious that even Cardassia ' s Central Command had no intel on it , the writers likewise had no idea it would lead to a battle later the same season . " " We had a vague idea of a first strike , " " clarified René Echevarria , " " but I don ' t think we knew more than that . " " It wasn ' t until the writers were plotting the story for subsequent third season episode that they realized they could make the military escalation be in preparation for a preemptive attack by not only the Obsidian Order but also the Tal Shiar against the Dominion . However , even at this point , the actual battle itself wasn ' t planned ; in fact , the Cardassians were to have been halted in their plans to combat the Dominion , due to Garak essentially blackmailing Tain . ( " " , p . 226 ) " " When Tain heard that , he thought his attack would lose the element of surprise , so he canceled the mission , " " Echevarria explained . ( " Captains ' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages " , p . 95 ) It was Michael Piller , in one of his last suggestions for the series , who encouraged the DS9 writers to " go fight the Dominion " in a second part of the narrative begun with " Improbable Cause " , an episode thereafter entitled . ( " " , p . 226 ) Thus , when the writers began to craft the story for " The Die is Cast " , the prospect of a monumental space battle loomed . Although the creative team decided to invent a machine that could prevent a Changeling from shape - shifting , the violent engagement remained conceptually viable to the writers , as opposed to having the enemies of the Dominion rid the Founders ' homeworld with the machines . Reasons why the writers still found the conflict acceptable for inclusion in the episode were that the machine was a prototype which the assailants had only one copy of and that the plans to the device were lost in the fray , also obliterating the fleet . ( " " , pp . 232 & 233 ) The writers felt it was important to put a lot of effort into showing the battle in " The Die is Cast " . " " We had set up all of this stuff about the invasion , the attack and all of those things in the first episode , " " remembered Ronald D . Moore , " " and when we got to the production meeting , we emphasized that we were really going to do a big space battle here and wanted to see it and have it blow our socks off . We didn ' t want to go cheap on this one . " " ( " Captains ' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages " , p . 95 ) Moore elaborated , " " We knew it had better pay off . I thought , ' Wow , this could be cool , because we ' re telling the audience that there ' s an invasion fleet that ' s going to do this massive thing . ' So we wanted as many warbirds as we could see , and a lot of Jem ' Hadar ships , and we wanted the " Defiant " to be in the middle of them all . " " ( " " , p . 234 ) Moore concluded , " " The visual effects guys kind of blanched a little bit , but they went for it . " " ( " Captains ' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages " , p . 95 ) Because depicting the optical - heavy event was very expensive , Gary Hutzel was assigned to ensure the battle didn ' t make " The Die is Cast " go over budget . Recalling an inexpensive method he consequently employed , Hutzel said , " " I shot transparencies of the Cardassian and Romulan ships on light boxes , and we ' flew ' those in the background . We kept the camera in constant motion so the audience wouldn ' t concentrate on them . " " On the other hand , the visual effects workers did imagine a particularly sophisticated shot . " " We wanted the scene to say that Sisko is really turning it on , " " reflected Hutzel , " " so we designed the shot to have the " Defiant " fly right through a Jem ' Hadar ship . " " ( " " , p . 234 ) The Battle of the Omarion Nebula was considered a ground - breaking conflict by DS9 ' s VFX artists , due to the extremely high quantity of ships portrayed in the incident . ( " " , p . 234 ) Ultimately , Ron Moore was also happy with the sequence , remarking , " " It ' s one of the best space battles we ' ve ever done . " " ( " Captains ' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages " , p . 95 )