The USS Essex (NCC-173) was a Federation Template:ShipClass starship that was in service with Starfleet in the mid-22nd century. In 2167, the Essex was commanded by Captain Bryce Shumar, the first officer was Commander Steven Mullen, and the security officer was Lieutenant Morgan Kelly. The Essex operated out of Starbase 12, under the sector command of Admiral Uttan Narsu. It carried a crew of 229.
In 2167, the Essex was destroyed with all hands aboard by an electromagnetic storm in the atmosphere of an M-class moon of Mab-Bu VI. The ship became trapped in the storm when non-corporeal criminals from Ux-Mal, who had been imprisoned on the moon centuries before, attempted to escape by possessing the Essex crew.
In 2368, the USS Enterprise-D detected the distress signal of the Essex, over 200 years old, and investigated the moon. The criminals impersonated the crew of the Essex and attempted to take over the Enterprise, but were unsuccessful. (TNG: "Power Play")