The Galaga submarine was first mentioned by Juliet after Tom and his team return to the Hydra Station after their theft of the Elizabeth, and after Colleen is shot by Sun-Hwa Kwon. While Mikhail Bakunin was being held prisoner by Sayid, Locke, Kate and Danielle, he mentions that he was first brought to the island on the submarine. He goes on to add that there is an underwater beacon that helps aid the navigation of the submarine.