The Battle of Deep Space 9 was the opening battle of the Dominion War, in which the combined forces of the Dominion and the Cardassian Union, led by Gul Dukat, launched an assault on the Federation-held starbase Deep Space 9. Although the station was captured by the Dominion, the battle was a strategic victory for the Federation because they successfully mined the Bajoran wormhole, preventing the Dominion from sending reinforcements to join the battle from the Gamma Quadrant. (DS9: "Call to Arms")
Following the annexation of the Cardassian Union around stardate 50560 (DS9: "By Inferno's Light"), the Dominion began fortifying their foothold in the Alpha Quadrant by sending weekly convoys of warships and troops through the wormhole. As time went on, Cardassian space became a veritable fortress teeming with Jem'Hadar soldiers and their Vorta overseers.
Although a technical state of war did not exist, and neither side had fully committed to immediate combat, numerous skirmishes took place along the border during this period. Aside from the Dominion's attempt to destroy the Bajor System using a trilithium bomb, the Jem'Hadar and the Cardassians attacked and destroyed numerous Federation and Klingon patrol ships in a sustained campaign across the border sectors. (DS9: "In the Cards")
In addition to the military advances, the Dominion made major inroads into the Alpha Quadrant politically as well, signing nonaggression pacts with several regional powers, including the Miradorn and the Tholian Assembly, and offered similar pacts to Bajor and other independent worlds in the area. The Dominion's greatest diplomatic achievement, however, was the signing of a nonaggression pact with the Romulan Star Empire, the third major power in the region. The Dominion's goal seemed clear: to isolate the Federation politically and militarily. Its classic strategy of divide-and-conquer seemed to be succeeding admirably; aside from the Klingon Empire, the Federation stood virtually alone in opposition to the Dominion. With peaceful means failing to slow down the Dominion's advance, Deep Space 9 Captain Benjamin Sisko observed, "...a war may be our only hope."
ProvocationWith its strategic advantage rapidly eroding, the Federation resolved to prevent the Dominion from sending further reinforcements into the Alpha Quadrant by mining the entrance to the Bajoran wormhole. Maintenance engineer Rom suggested using self-replicating mines equipped with cloaking devices for the blockade; not only would such a minefield be undetectable to approaching ships, but it would also be virtually indestructible, because each mine destroyed could be replaced by other mines in the vicinity. Miles O'Brien and Jadzia Dax quickly developed a working model, and the USS Defiant immediately began laying the minefield.
This action could be seen as nothing less than a provocation for war, however, and the Dominion's primary overseer, Weyoun, demanded that the mining of the wormhole be halted immediately. Captain Sisko flatly refused.
An intricate dance of lies and intimations began: Weyoun claimed that the Cardassians, having suffered terrible damage during the Klingon-Cardassian War, required massive assistance in rebuilding their infrastructure and defenses following the Klingon invasion. Sisko played along, claiming to have had no idea that the Cardassians' situation was so bad. The two representatives arranged a deal, in which the Federation would remove the minefield, and the Dominion would restrict further convoys to nonmilitary personnel and material. However, both sides were merely using this repartee as a ruse to buy time — Weyoun to prepare the Dominion fleet for the attack, and Sisko to complete the minefield.
With war imminent, Sisko, acting as Emissary, requested that the Bajoran Provisional Government sign the non-aggression pact offered to them by the Dominion, ensuring the planet and its people were kept out of the now-inevitable conflict.
Intent on preventing its lifeline to the Gamma Quadrant from being blocked, the Dominion launched a massive assault fleet towards Deep Space 9, with Gul Dukat himself in command. For reasons then unknown, the Federation had not reinforced its position at DS9, leaving only the Defiant and the IKS Rotarran to supplement the station's defenses. Anticipating the enemy attack, Sisko ordered the Rotarran to patrol the border and provide advance warning when the Dominion fleet approached.
The Dominion assault force comprised nearly 300 Jem'Hadar and Cardassian warships. Captain Sisko confidently refused Dukat's offer to surrender, and both sides prepared for the onslaught.
As the Dominion fleet opened fire, Weyoun and Dukat were unpleasantly surprised to find DS9's shields holding up under the barrage — Federation deflector shields had previously been impotent at defending against the Jem'Hadar's phased polaron beam weaponry. Dukat ordered more ships to open fire on the station.
Meanwhile, the Defiant herself was coming under fire as she was laying the minefield. The Rotarran provided interference and covering fire, giving the Defiant enough time to complete and activate the minefield, sealing off the wormhole.
Using his knowledge as the station's former commanding officer, Dukat was able to cut main power to DS9's shields. With the wormhole now blocked, and the station becoming an impossible position to hold, Captain Sisko ordered all Starfleet personnel to evacuate Deep Space 9. As Dukat ordered his reserve units to enter the battle, the station's crew boarded the Defiant and the Rotarran, taking all sensitive equipment with them and leaving the station in the hands of the Bajoran Militia.As the evacuation neared completion, Sisko addressed the remaining station residents on the Promenade, promising, "I will not rest until I stand with you again, here, in this place where I belong."
Once the Defiant and the Rotarran had safely departed the station, resistance elements remaining on the station activated Program Sisko 197, which totally sabotaged the station's computer and power systems, leaving the station a nearly lifeless hulk. The Dominion and Cardassian troops boarded the station, officially reclaiming Terok Nor, which they had abandoned in orbit of Bajor five years previously.
AftermathDukat and the Dominion may have captured Deep Space 9 from the Federation, but the battle was ultimately nothing but a pyrrhic victory, because the minefield operated independently from the station and proved resistant to all initial attempts to dismantle it. Likewise, the sabotage of the station itself meant that it would serve little function other than as a command and supply outpost behind the front lines.
In addition, while the Dominion had thrown its full force towards capturing the station, a combined Starfleet-Klingon taskforce crossed the border into Cardassian territory and destroyed the shipyards at Torros III, nearly unopposed. This victory would have much greater impact in the short- and mid-term course of the war, as the Dominion's shipbuilding capabilities were seriously affected by the loss of that major facility.
Ultimately, the station would be recaptured by a joint Starfleet and Klingon assault in the Battle of Bajor approximately five months later.