First Battle of Deep Space 9
The First Battle of Deep Space 9 was the prelude to the  of 2372 and 2373. In early 2372, a Klingon task force led by Chancellor Gowron and General  launched an attack on the Federation space station of Deep Space 9, in an attempt to force Captain Benjamin Sisko to relinquish the Cardassian Detapa Council members under his protection. The Klingons had underestimated the station's new defenses and were unable to take the station before the arrival of Starfleet reinforcements. Faced with the prospect of considerable losses, a war on two fronts, and the looming threat of the Dominion, Gowron ordered his forces to withdraw.

Prelude 
After the Battle of the Omarion Nebula in 2371, the Cardassian Union was in a state of turmoil. For centuries, the Obsidian Order had kept an iron grip on all levels of Cardassian society, keeping the status quo firmly in place. With the Obsidian Order decimated by the Jem'Hadar, the Cardassian Underground had finally been able to make headway against the oppressive rule of the Central Command. Faced with growing unrest and civil uprisings, the Central Command sealed the borders of the Cardassian Union to focus their attention on the rebellion. Despite their efforts, early in 2372 a popular revolt overthrew the Central Command and restored the power of the civilian Detapa Council. ()

Meanwhile, the Klingon Empire had been infiltrated by a Founder, masquerading as General Martok. This Founder, taking advantage of the paranoia effected by the strong possibility of Changeling infiltration, misled the Klingon High Council into concluding the Cardassian uprising could have succeeded only with Dominion assistance – and, with ironic mendacity, he proclaimed the Detapa Council had been replaced by Founders. The Changeling advocated for a Klingon invasion of the Cardassian Union to neutralize the "Dominion threat". His proposal came at a time when many Klingons believed that decades of peace had led them astray and weakened the Empire. As such, the invasion plans were eagerly embraced by Klingons hoping for a return to the gloried old ways of war and conquest. ()

When preparations were complete, a Klingon task force of over twenty warships, led by the flagship , arrived at Deep Space 9, ostensibly to aid the Federation forces guarding the wormhole. Once their true purpose was discovered, Captain Benjamin Sisko urged Martok to reconsider their plans. Disregarding Starfleet's warnings, the Klingon fleet proceeded into Cardassian space, commencing the Klingon-Cardassian War. Bound by their alliance, the Federation could do nothing to interfere, although Sisko "unofficially" sent an advance warning to the Cardassians through Elim Garak. A few days later, the Federation Council condemned the Klingon invasion. Outraged that his ally had refused to support him in "defending the Alpha Quadrant" from the Dominion, Gowron withdrew from the Khitomer Accords and broke off all diplomatic contact. ()

Flight from Cardassian space 

Although the Cardassian fleet mobilized in time thanks to Garak's warning, the speed and magnitude of the Klingon advance broke through their lines a short time after the invasion began. The Klingon invasion rapidly progressed to the point of the fleet being only 52 hours from Cardassia Prime itself. Standard Klingon procedure for the invasion of the planet would have been to execute the Detapa Council and install an Imperial Overseer, which would effectively end the Cardassian Union. To prevent this from happening, Sisko contacted Gul Dukat, the new chief military advisor to the Detapa Council and advised him to evacuate the Council to Deep Space 9. Dukat agreed, and left Cardassia with the Council members aboard the cruiser Prakesh.

At the same time, Sisko took the  into Cardassian space to rendezvous with Dukat, using its cloaking device to hide from the Klingon forces (in violation of the terms of its loan from the Romulans). When they arrived they found that the Prakesh had been intercepted by three Birds-of-Prey, and was under heavy fire. The Klingons ignored Sisko's order to stand down, and opened fire on the Defiant. With those shots, two decades of peaceful co-existence came to an abrupt end. Amid the fighting, Dukat managed to contact Sisko and informed him that while he and the Council members were alive, the Prakesh had already lost all engine, weapon and shield power, and was in grave danger of suffering a warp core breach.

The Defiant engaged the Birds-of-Prey, buying time for the stricken Prakesh while a  attack cruiser entered the battle. Using a modified tractor beam to deflect some of the cruiser's fire, the Defiant lowered its shields long enough to transport the Detapa Council members aboard. The Prakesh exploded shortly afterwards as the Defiant headed back for Deep Space 9 at maximum warp, the two remaining Klingon warships in close pursuit. With this development, a Klingon force returned from Cardassian territory and headed to the Bajoran system. Aboard the Defiant, Doctor Julian Bashir administered blood screenings of all the Council members and verified that they had, in fact, not been replaced by Founders. ()

The Battle 

When the Defiant reached Deep Space 9, they found several dozen Klingon warships in an attack formation waiting for them beyond the station's shield perimeter. The Bird-of-Prey and the attack cruiser which had pursued the Defiant all the way from Cardassian space, joined the Klingon fleet. Gowron and Martok, aboard the 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 was irrelevant to Gowron, who asserted that the Alpha Quadrant would be safer with the Klingons in control of Cardassia. Sisko gave a last warning, informing Gowron that over the past year, the station had been receiving state-of-the-art tactical upgrades due to the constant threat of Dominion attack. These upgrades included the installation of numerous new torpedo launchers, phaser emitters, and shield generators, as well as a stockpile of five thousand photon torpedoes. Gowron scoffed at this threat and ordered his forces to advance, announcing "CHEGH-chew jaj-VAM jaj-KAK" – "Today is a good day to die."

The first wave of Klingon ships opened fire on the station, moving to surround it on all sides. The station's weapons returned fire, destroying eight Klingon warships in the opening volley and heavily damaging several more. Undeterred, the Klingon forces pressed on their attack. Realizing the futility of additional negotiations with the Klingons, Sisko ordered the station to fire at will. Surprised but undaunted by the station's upgraded defenses, Martok ordered the Negh'Var and several support cruisers to concentrate their fire on the station's shield generators. The Negh'Vars heavy disruptor cannons scored several direct hits, disabling two of the generators and opening a gap in the station's shields.

Seizing this opportunity, Klingon boarding parties began materializing in the operations center, Promenade, habitat ring, and Lower Pylon 3. Small-scale firefights and hand-to-hand combat erupted throughout the station, although civilian casualties were minimal as Sisko had evacuated non-essential personnel to the emergency shelters prior to the battle. The Klingon forces additionally found themselves hindered by force fields erected between all major access points of the station. After the command crew repelled the Klingon boarding parties in Ops, Chief Miles O'Brien managed to restore Deep Space 9's shields and prevent additional Klingon troops from reinforcing their positions on the station. In the meantime, Odo and his security forces had managed to contain the Klingon troops in the habitat ring, Promenade and Lower Pylon 3, though Odo himself was unsure how long they could continue to do so. 

As the Federation personnel in Ops returned to their posts, another wave of Klingon ships was detected entering sensor range. However, a Starfleet relief force of six starships, consisting of the , two  starships, one , and two more starships led by Admiral Hastur aboard the Venture, also entered sensor range. Realizing that the Federation relief force would arrive at the station before the Klingon reinforcements, Sisko contacted Gowron again, hoping that the chancellor would see how mutually destructive continuing his attack could become. Martok insisted that the Klingons could still prevail, but Sisko and Worf both warned him that continuing his assault would result in the Klingon Empire entering a protracted, all-out war with both the Cardassians and the Federation, which would only serve to weaken them all and pave the way for the Dominion conquest. Gowron recognized the truth of the Starfleet officers' argument and ordered the Klingon fleet to stand down and withdraw. ()

Aftermath 
The battle at Deep Space 9 ended indecisively, as even though the Klingons had failed to capture Deep Space 9 or the Detapa Council, their offensive against the Cardassians continued. After the battle, the Detapa Council was safely returned to Cardassia Prime, though their rule would be short. Less than two years later, the devastating war with the Klingons would lead Dukat into delivering the Cardassians into the hands of an even more oppressive power than the Central Command: the Dominion. ()

For the Federation, an all-out war with the Klingons had been averted, but the alliance that had unified the two powers in friendship for decades was lost. The ensuing low-level Federation-Klingon conflict would escalate into open warfare in late 2372; it would end with a cease fire several months later, after Martok was exposed as a Changeling, but only after mounting casualties on both sides. Beginning with the Battle of Deep Space 9, the Founders had nearly succeeded in their goal of irreparably destroying the Federation-Klingon alliance, the only power which could have stood against a Dominion invasion. Fortunately for the Alpha and Beta Quadrants, the two powers were able to reconcile in time, and turn their attention back towards the Dominion, but not until after the loss of a great many lives. ()

cs:První bitva o Deep Space 9
de:Schlacht von Deep Space 9 (2372)
fr:Première Bataille de Deep Space 9
nl:Eerste slag om Deep Space 9
Deep Space 9, First Battle of