Karen Farris was a member of the elite Starfleet Academy cadet group Red Squadron in 2374. She was assigned to the USS Valiant on a training mission prior to the outbreak of the Dominion War. When the war began, the Valiant was trapped behind enemy lines and severly damaged in a Cardassian attack that killed all of the officers. Farris was given a field promotion to commander and a position as first officer by acting captain Tim Watters.
Eight months later, the Valiant attempted to destroy a massive Jem'Hadar battleship. Farris manually guided two modified torpedos that were designed to destroy the primary support braces of the antimatter storage system of the battleship. Farris was successful in hitting the target, but the weapons were ineffective. She was killed along with 34 other members of the crew when the battleship destroyed the Valiant. (DS9: "Valiant")