Former called Hydrobase, the floating fortress inhabited by Sub-mariner and his band of Amphibians.
Afterthat, when the Avengers were told they could no longer use their Avengers Quinjetsin Manhattan, due to lack of official clearance, Stingray contacted the team and offered them the opportunity to store their Quinjets on Hydrobase. As a token of gratitude, Stingray was awarded reserve membership with the team.
Following a subsequent attack on Avengers Mansion in Manhattan by the Masters of Evil, the Avengers decided to permanently relocate their operations and their mansion to Hydrobase.
After housing the Avengers for an extended period of time, Hydrobase was eventually destroyed by Doctor Doom and his robotic army when they attacked the island during Acts of Vengeance. The island sunk to the bottom of the ocean. Although both Quasar and Sub-Mariner tried to help Stingray salvage much of the island, their attempts were mostly fruitless.
At some point, the island was raised from the ocean floor, although remained unused and unmaintained afterwards. The artificial island, mostly ruins by this point, were later used as a meeting place for the Illuminati.