The First Battle of Chin'toka was the first offensive launched by the allied forces of the United Federation of Planets, the Klingon Empire, and the Romulan Star Empire into territory held by the Dominion and the Cardassian Union during the Dominion War. The battle, fought in late 2374, was a tactical and psychological victory for the allies, but failed to lead to a general invasion of Cardassian space. (DS9: "Tears of the Prophets")
Apart from the short (and successful) campaign to retake starbase Deep Space 9 in the Battle of Bajor about eight months previously, the Federation and the Klingons were fighting a wholly defensive war. Key planets including Betazed, Coridan, and Benzar all fell to the Jem'Hadar, while the core worlds of Vulcan, Alpha Centauri, and Earth were coming into range of the Dominion war machine.
However, with the sudden entry of the Romulans into the war (c.f. DS9: "In the Pale Moonlight"), the allies had enough combined firepower to launch a full offensive on Dominion-held territory. Starfleet Command, in conjunction with the Klingon and Romulan high commands, agreed that the war could be won only by taking the war into enemy territory.
After some heated deliberation at Deep Space 9, the allies chose the Chin'toka System as the target for their attack. (Alternative targets included the Ventani System and the Torg'Q System.) Chin'toka was chosen because the Dominion had drastically weakened the complement of warships defending the system — only five squadrons of Jem'Hadar attack ships were left to defend Chin'toka, while the rest were sent to fight on the Romulan border. Admiral Ross, General Martok, and Senator Letant ordered an immediate buildup of warships at Deep Space 9 for an attack on Chin'toka.
However, the Chin'toka System was not left as undefended as the allies believed. The Cardassians had developed a new type of orbital weapon platform that compressed a huge amount of weaponry into an independently-deployable hull barely fifty meters long. The platforms were protected by regenerative shields, and armed with 3 heavy disruptor cannons and 1,000 plasma torpedoes.
The allies' intelligence detected the deployment of these weapons barely three days before they were scheduled to go online. However, because of the lack of other vulnerable targets, the decision was made to take the small window of opportunity available and attempt to destroy the platforms before they became operational.
As the combined fleet entered the Chin'toka System, it seemed as if the allies' projections had been true — Chin'toka was practically undefended and the automated defenses were offline. Quick victory appeared within reach, with the odds overwhelmingly in the allies' favor.
The small contingent of Jem'Hadar attack ships defending the system had little care for the odds, though, and brazenly attacked the fleet's flank. In the space of just two minutes, the Jem'Hadar ships managed to cripple or destroy at least 15 Klingon warships — many by ramming the Klingons directly. Undaunted, the fleet advanced into the midst of the deactivated platforms and proceeded to demolish them without resistance.
However, the Cardassians had prepared a trap for the allies, making it appear that the weapon platforms were deactivated. Moments after the fleet entered orbit, the platforms flared to life — the defense network had already been completed, and the Cardassians had merely been waiting for the allies to close to point-blank range before opening fire.
The orbital weapons platforms' effect proved devastating — protected by their powerful regenerative shields, the Cardassians could pour heavy fire upon the attacking fleet with practically no loss taken themselves. Several dozen starships were disabled or destroyed by the platforms' furious barrage. Rather than retreat, however, Captain Sisko chose to continue the fight, correctly believing that if the defense platforms could be defeated, then the system would fall to the allies.
In the chaos of the battle, an unusual anomaly was detected — none of the weapons platforms carried their own power source, but were instead powered by a single central generator. This generator was located on a small asteroidal moon in a low orbit around Chin'toka II-A. If it could be destroyed, the platforms would be powerless.
The allies attempted a frontal assault, but proved unable to penetrate the asteroid's defensive shields, even with the sustained fire from multiple starships. Chief Miles O'Brien of the USS Defiant proposed tricking the automated platforms to fire on their own power source. Using the ship's deflector array, O'Brien imprinted a Federation warp signature on the generator, making it appear as if it were an enemy vessel. The orbiting platforms immediately locked onto this large new signal, pouring fire into the asteroid and quickly destroying it.
Without more incoming power, the orbital platforms quickly fell silent and were once again easy targets for the allied fleet. With near-orbit space secured, General Martok began transporting ground troops to the surface of both planets. Although there was some resistance from Dominion and Cardassian soldiers, the major population centers quickly fell to allied control.
Although the hoped-for grand offensive into Dominion territory failed to develop after Chin'toka, the battle nevertheless had major consequences for the conduct of the remainder of the war. The Dominion was faced with their first major defeat since the Battle of Bajor six months previously, as well as the spectacular failure of the orbital weapons platforms, which had been a key plan for the Cardassians to upgrade their defensive capabilities.
Perhaps most importantly, however, the allies had the opportunity to examine large caches of Dominion weapons and technology (most notably Relay Station AR-558), which provided a crucial boost on the allies' knowledge of enemy capabilities. However, although the Chin'toka System was nominally in Federation control, it was constantly under attack by Dominion forces. (DS9: "The Siege of AR-558")
Ultimately, the first Battle of Chin'toka proved to have the most impact in terms of morale, as well as reversing the nearly-constant Dominion advances of the preceding six months as more Jem'Hadar had to be diverted for defensive reinforcements. Although the system was lost to the Dominion in the Second Battle of Chin'toka approximately eight months later, Chin'toka played an important role in the course of the entire war.