Vice admiral
From Halopedia, the Halo wiki
Template:Rank Infobox Vice Admiral is a senior commissioned officer rank of the UNSC Navy.
It is equal with the rank of Lieutenant General in the UNSC Marine Corps.
In informal settings, Vice Admirals are typically referred to simpy as "Admiral".
A Vice Admiral may be also referred to as a "three-star Admiral" to distinguish it from the other ranks of Admiral; so named for the three star rank insignia worn on the uniform.
Vice Admirals generally command the numbered fleets around UNSC controlled space, in charge of the naval components of each of the regional unified commands. Of the five numbered fleets, four have command ships which act as the Vice Admiral's flagship.Template:Fact
Sources
In reference to the above image -- This is the U.S. Navy insignia for a Vice Admiral. The UNSC Navy uses the same insignia. -- Reference: Halo: Ghosts of Onyx, page 104.