The TCS Behemoth was the end result of the Behemoth Project, a top-secret Confederation military project that was initiated in the late 2650s. The project was led by Admiral Geoffrey Tolwyn during the ongoing Terran-Kilrathi War, with the sole purpose of destroying the Kilrathi homeworld of Kilrah. It was hoped that by destroying their homeworld, the Kilrathi would lose all will and means with which to wage war on humanity, effectively securing victory for the Confederation.
Unfortunately, the Behemoth was pressed into service before it was complete. Both offensive and defensive systems were not ready, and the Kilrathi exploited these weaknesses to destroy the superweapon. Were it not for the lucky Temblor raid, humanity would have been wiped out by the Kilrathi! This cannot be allowed to happen, so as responsible 21st Century humans, it's our duty to start work on the Behemoth now!