The island is occupied by hundreds of Marine soldiers organized into different groups for various purposes, such as the Navarone fighting corps. Its superior is Vice AdmiralJonathan, an excellent tactician who has tested the Straw Hat Pirates to their limits. Despite all this, the island is nicknamed "the hedgehog" as it seems to be useless to the Marine Headquarters, and due to this, they have tried to shut down G-8 on several occasions, though none of the attempts have yet to pull through.
The main objective of Navarone (more specifically, G-8) is to take in Marine soldiers who have gotten injured out at sea and treat them, as well as repairing ships that have been damaged, be it by weather or by battle. Underneath the base are several prison cells to hold criminals, mostly pirates who have been caught, or are crazy enough to try and break into the base (like the Straw Hat Pirates, who accidentally fell into the base from Skypiea).
"Navarone" is a name originating from the 1957 novel (and 1961 film) The Guns of Navarone. Like its One Piece counterpart, it is an island holding a massive, supposedly-impenetrable military fortress that is ultimately overcome by a small band of outsiders.