Enigma Sector is a vast region of space that lies directly rimwards of Sol Sector. Enigma Sector consists of the Asimov, Grills, Isaac and Roddenberry Quadrants. The Enigma Sector included the star systems Adams, Argarrio, Arraman, Axius, Blish, Blake, Bradbury, Brin, Cabrea, Callimachus, Card, Clarke, Crichton, Damioyn, Defiance, Drake, Dyson, Ellison, Enigma, Exile, Facin, Fiddler's Green, Foster, Gardel, Gerrold, Ghorah Khar, Gibson, Gwynedd, Halderman, Harrison, Heaven's Gate, Heinlein, Herbert, Hilleman, Irving, Kalvan, K'arakh, K'tithrak Mang, Langston, Lucas, McCaffrey, Midian, Muspelheim, Mustakas, Niffleheim, Niven, Novaya Kiev, Pembroke, Piper, Pohl, Pournelle, Racene, Rarkath, Repleetah, Rigel, Robinson, Salayna, Shelton, Speradon, Spielburg, Steakly, Sterling, Stirling, Talbot, Telamon, Tesla, Trk'Harna, Vespus, Vonnegut, Wetland, and Zelanzny.
Enigma was strategically valuable in the Terran-Kilrathi War due to its vast network of jump points, granting all sides uncontested access to enemy star systems. If the Kilrathi were to conquer Enigma, they would gain access to several major colonies and even Earth itself. The Enigma Sector Campaign of the 2650s and 2660s saw both sides heavily engaged for control of the sector, leading to some of the most furious battles fought in the War. The TCS Tiger's Claw was assigned to destroy the Kilrathi Sector Command at K'tithrak Mang in the year 2656, a mission which ended in failure when the carrier was lost with all hands to a flight of stealth fighters during its final approach. The next eleven years saw both sides stalemated in their campaign as the Terrans fought desperately to protect their worlds while the Kilrathi struggled to contain the separatist rebellion on Ghorah Khar, which quickly aligned itself with the Terrans.
The Kilrathi continued to produce and field their new stealth fighters in secret throughout Enigma, where they would constantly harass Terran interests and leave no survivors, leaving the Confederation unaware of the menace responsible for the loss of the Tiger's Claw.
The TCS Concordia, the flagship of the Confederation Navy was assigned here under the command of Vice Admiral Geoffrey Tolwyn by the year 2661, with the intention of crushing the Kilrathi presence in Enigma.
The Battle of Repleetah was fought here from 2653 to 2663, during which Terran and Kilrathi ground forces engaged in one of the longest and bloodiest campaigns of the entire War. Both sides committed tens of thousands of troops towards a primarily land-based battle for control of the planet, despite its lack of strategic value. The survivors committed to one final engagement in 2663, ending with the deaths of every remaining soldier on Repleetah.
The campaign for Enigma reached its height by 2666, when the Kilrathi renewed their push for control of the sector. The pilots of the TCS Concordia fought off the invaders in several decisive engagements, including Ghorah Khar, Heaven's Gate, and Novaya Kiev. In 2667, the Concordia launched a major assault on K'tithrak Mang. Disgraced captain Christopher Blair flew with distinction in the engagement, proving the existence of stealth fighters and launching his own assault on K'tithrak Mang. In this battle Captain Blair destroyed the Kilrathi starbase, achieving victory for the Terrans in the Enigma Campaign. However, even with their hold over the sector broken the Kilrathi would continue to battle for control of Enigma for the rest of the War.
The Ghorah Khar Campaign would continue in Enigma where the Kilrathi struggled to stop the rebellion that had now spread to other planets within the Empire, with the Terrans rushing aid to their new allies. The Terrans finally secured the freedom of the separatists, but this success was blunted by the Kilrathi's concurrent blitzkrieg assault on the Deneb Quadrant in the neighboring Epsilon Sector.
By the final year of the Terran-Kilrathi War the Terrans were once again on the defensive on all fronts, and the Kilrathi launched many forays into Enigma as they consolidated their recent victories in the conflict. The TCS Concordia was lost when it was ambushed by a Kilrathi strike force above Vespus in 2669, crashing onto the planet's surface. These advances were largely rendered moot however with the destruction of Kilrah later that year at the hands of Colonel Christopher Blair, signalling the end of the Terran-Kilrathi War.
Enigma continued to be a theater of action after the war's conclusion with the outbreak of the Border Worlds Conflict in the 2670s. Several systems in Enigma would come to pledge their allegiance to the fledgling Union of Border Worlds, threatening a major conflict with the Terran Confederation. The true instigators of the conflict, the Black Lance, were headquartered out of the unpopulated Axius System by 2673. That same year, Telamon was subjected to the Gen-Select Bioweapon that saw nearly its entire population wiped out by the rogue Terran faction. A Border Worlds-led intervention however halted the impeding war by exposing the conspiracy.