Lieutenant Commander Carolan served as transporter chief onboard the USS Challenger. She was originally to serve as the ship's second officer, a position that was given to Geordi La Forge when he was temporarily assigned to the Challenger. Carolan was assigned as first officer when La Forge was promoted to captain and given command of the Challenger, since Captain Montgomery Scott had to step down due to health issues, Commander Tyler Hunt (the ship's original first officer) had been killed in action, and Lieutenant Commander Reginald Barclay had turned down La Forge's offer to be his first officer. (TNG novel: Indistinguishable from Magic)