Klingon forces, including the flagship Negh'Var, attack Deep Space Nine
The Negh'Var fires its main disruptor cannon, knocking out a shield emitter
After the rescue of the Cardassian Detapa Council from Klingon attack, the USS Defiant set course for Deep Space Nine. When the Defiant arrived, they found several dozen Klingon warships in attack formation, waiting for the beyond the station's shield perimeter.
Gowron and Martok, aboard the flagship Negh'Var, sent an ultimatum to Sisko: surrender the Council members, or have them taken by force. Sisko refused, informing them of the results of the blood screenings. Not surprisingly, the fact that the Council members were not changelings meant little to Gowron, who asserted that Cardassia would be better off under Klingon control. Sisko also warned that the station's weapons systems had been upgraded. Gowron's response: "Today is a good day to die."
The first wave of Klingon ships opened fire on the station. The station's weapons returned fire, destroying eight Klingon ships and heavily damaging several more. The Klingons pressed their attack with Sisko responding to "fire at will" at the Klingons.
Martok then ordered the Negh'Var and several support cruisers to concentrate their fire on the station's shield generators. The Negh'Var's heavy disruptor cannons scored several direct hits, disabling two of the generators and opening a gap in the station's shields.
At this time, Klingon boarding parties materialized aboard the station, notably in Ops and on the Promenade. Small scale firefights and fierce hand-to-hand combat erupted through the station. However, with Sisko's preparations, the Starfleet and Bajoran officers were able to contain the Klingon boarding parties. Sisko and other command staff regained control of Ops, allowing Chief Miles O'Brien to restore Deep Space Nine's shields and prevent additional Klingon boarding parties from materializing.
As the Klingon attack faltered, a Starfleet relief force of six starships, led by Admiral Hastur aboard the USS Venture, arrived to support Deep Space Nine. Sisko was able to convince Gowron to stand down his fleet, stating that this fighting was exactly what the Dominion wanted...chaos in the Alpha Quadrant. Martok insisted on pressing the fight, but was eventually overruled by Chancellor Gowron.