G-1 is a Marine Base that was located in the New World, now on Marineford (where Marine Headquarters used to be), where Vice Admiral Momonga is stationed.
After the events of the Battle of Marineford, the base switched locations with the Marine Headquarters at Marineford, as Fleet Admiral Sakazuki's desired to have the Headquarters in the sea the Yonko are in order to challenge their domination within the second half of the Grand Line.
Its former location, now called New Marineford, is said to be exactly symmetrical to Marineford on the other side of the Red Line.
- ↑ 1.0 1.1 1.2 1.3
One Piece Manga and Anime — Vol. 61
Chapter 598 (p. 10) and Episode 517,
Humphrey tells Nami that the new fleet admiral moved Marine Headquarters to the New World.