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 - The Janus Gate novel: 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").