There are 9 unique codex entries in the Achievement: Titles section on the Republic Fleet. 1 is accessible to all players regardless of class or faction and 8 are unobtainable.
Red Rhombus is obtained from speaking with Major Cobus during "Terror from Beyond" mission.
Codex type: Achievement: Titles | Faction: Both | Class: All
Associated Achievement: None
the Commando is unobtainable.
Codex type: Achievement: Titles | Faction: Republic | Class: Trooper
Associated Achievement: None
the Guardian is unobtainable.
Codex type: Achievement: Titles | Faction: Republic | Class: Jedi Knight
Associated Achievement: None
the Gunslinger is unobtainable.
Codex type: Achievement: Titles | Faction: Republic | Class: Smuggler
Associated Achievement: None
the Sage is unobtainable.
Codex type: Achievement: Titles | Faction: Republic | Class: Jedi Consular
Associated Achievement: None
the Scoundrel is unobtainable.
Codex type: Achievement: Titles | Faction: Republic | Class: Smuggler
Associated Achievement: None
the Sentinel is unobtainable.
Codex type: Achievement: Titles | Faction: Republic | Class: Jedi Knight
Associated Achievement: None
the Shadow is unobtainable.
Codex type: Achievement: Titles | Faction: Republic | Class: Jedi Consular
Associated Achievement: None
the Vanguard is unobtainable.
Codex type: Achievement: Titles | Faction: Republic | Class: Trooper
Associated Achievement: None