The main military organization of this empire was the Sargasso War Fleet, which was a space fleet that Sirena herself lead into battle against Oa, which she attempted to conquer, subjecting it to her empire, but she was stopped by the Green Lantern of Sector 2814, better known as Hal Jordan.
Seat of the Empire
Known Subject Races
The only known subject races of this empire were the inhabitants of Sargasso itself, as listed above. Although since Oa was nearly conquered, the Oans would have became subjects; - if not for Green Lantern.