Fuel cell
From Halopedia, the Halo wiki
The Fuel Cell is a grey barrel located behind the left wing on the Ghost that is destroyable only on Halo 2 and 3.
It provides the engines and the twin plasma cannons of the Ghost with its stored plasma supply.
It is only worth noting because an explosion big enough to destroy the Ghost can be triggered if it is hit with a single bullet from such weapons that are able to cause a Headshot.
File:Halo 3 ghost angle.jpg
The fuel cell located above the left wing.
