In 2266, Jaeger was part of a fifteen-man survey team that was assigned to Tlaoli IV. When the team discovered a number of wrecked starships on the planet's surface, Jaeger gathered all the lieutenants together and they all decided to send a team into the caves to investigate. Jaeger led the team himself, but they soon lost contact with the other teams due to the transperiodic ores on Tlaoli IV's surface. (TOS novel: The Janus Gate: Present Tense).
In 2267, Jaeger accompanied a landing party to the surface of Gothos to search for the missing Captain Kirk, after he was captured by the omnipotent being known as Trelane. (TOS episode: "The Squire of Gothos").