- See Brennan for other articles with titles that contain, either by relationship or by coincidence, this character's surname.
Brennan was assigned to the Enterprise's security division. In the year 2269, Brennan was leader of a security team that boarded the starship Ransom Castle after a Romulan attack. Brennan and his men located several injured crewmembers locked in cargo holds while pursuing Romulan lifeform readings. (TOS novel: The Great Starship Race)
- Brennan was referred to simply as "officer" which would seem to indicate he was an ensign or lieutenant, but his exact grade was not specified.