Fron Island is a non-canon island in the New World, near Totto Land. Vice Admiral Prodi commands the Marine Base G-F here. The island was initially seen on a map in Zou that Nami analyzed. However, it has yet to be named outside of Weekly Shonen Jump.
One Piece Episode 780 "A Hungry Front - Luffy and the Marine Rookies!"
At some point in the past, a Marine Base was built on Fron Island to keep a watch on Big Mom.
A ship carrying reserve Marine personnel, including Captain Grount, landed at Fron Island. While everything was going on, the Straw Hat Pirates sneaked into the island for food. However, their presence was soon discovered, and Monkey D. Luffy was cornered in the cafeteria.
The Straw Hats fought out of the cafeteria and stormed food storage but were encountered by some Marine personnel. The Straw Hats beat them and defeated Vice Admiral Prodi's soldiers on the coast. Bonham, Zappa, and Grount came to the coast to make a final stand but were ultimately defeated, and the Straw Hats fled the island.
Fron Island has a round shape and a rough beach with several tall rock pillars. Inside it lies a massive circular plateau with a forest growing on top and a vast basin in the middle containing a Marine base. On one side of the island, a little inlet leads to a gate leading to an entry through the plateau into the ground.
A large chunk of Fron Island is home to a Marine base, and it has a huge gate within the plateau through which marine ships can enter. The facility comprises various structures, including the main site of operations and a warehouse that stores food supplies.
These are the main Marine Personnel commanding the Fron Island.
Vice Admiral Prodi
Captain All-Hunt Grount
Lieutenant Ant De Bonham
The name of the island is a pun: It can be interpreted as the Japanese pronunciation of the word "front" when read with the Japanese suffix "-to" (島 island). This hints at the fact that it is a front for Big Mom.
Fron Island was built to keep an eye on the former Emperor Big Mom.
Marine Rookie Arc is the Marine filler arc in One Piece.
Captain All-Hunt Grount is the main villain in the Marine rookies arc.