you first go to steven to get dive and dive dvie
you have to dive underwater by sootopolis city and you have to go in the little cave underwater where youll find the sud and then you surface there.
you will find team aqua in the under water cavern near the dive point in sootopolis
a sapphire from an uncut sapphire by using a chisle on it, and smelt a gold bar into a sapphire necklace.
The ruby and sapphire are on fire red and leaf green don't worry about the in ruby sapphire or emerald.
Catch the submarine Pokémon and beat the crap out of the Elite Four.
go get a life
Seafloor cavern in route 128
it is in team aqua's base (the one where they had the submarine)
you first go to steven to get dive and dive dvie
he goes to his underwater hideout cave.
The submarine belongs to that scientist guy, you're not allowed on, you have to learn dive then find the place they are exploring, but there is a scale model of the sub in the museum.
in the cave where team magma escapes you in the submarine next to lilycove city
Go to the submarine and press B. You'll notice you can get up there. If you are above, you'll need to explore a cave with team aqua in it.
Go back to Slateport town. Inside the ferry building, you will find captain stern and the submarine being robbed by Team Aqua.
Team aquas base where they first hide the submarine. It's in one of the rooms
there a dive area and once you dive there, there youll find the submarine but you really need to look. the entrabce is like entering a cave underwater