The Original USS Omega, Under the command of General Kal Booth entered a rift that lead to the mirror universe. After they went through, the rift closed behind them trapping them. General Booth and his crew fought for five years attacking the Terran Empire when and where they could.
Eventually, with their ship severly damaged, they were able to steal a ship from the Terran Empire - their version of the Omega, Luna Class - and open a rift back to their own universe. Now, General Booth is looking for a crew for this new ship.
Now armed with advance tech, the ship has been given the assignment to ensure the security and the safety of Starfleet and the Federation.