Final Fantasy VII Walkthrough – Junon Underwater Reactor
Items: Battle Trumpet, Scimitar, Leviathan Scales, and Tifa's God Hand
When you go into town you can pay ten Gil to ride the elevator into the Shinra section of Junon. When you run through the area you'll have to fight Shinra enemies and they're fairly tough for just regular fights so be prepared. While you run through Cloud will notice that there's something missing. You'll come to the place near to where you joined the parade, a sort of corridor and you'll see a drill leader and some troops saying "its this way to the underwater reactor" etc. Follow them into the lift then go along the sea tunnel to the reactor.
Make your way through and you will encounter Shinra Soldiers along the way and you'll eventually come to a hall there will be an alarm you can trip, it doesn't make a difference if you trip it or you don't. Take another elevator down to the Ocean Floor then continue down the walkway. When you arrive you'll see the huge materia being removed and loaded into a submarine. Run to the submarine-docking bay, when you arrive you will meet Reno, again, he'll leave you fighting a boss.
Boss: Carry Armour
This one's really annoying because his arm(s) grab one or two of your characters, rendering them useless, if you destroy the arm holding a character it should drop them after a few bashes or you can simply kill the character then revive them. Cast wall for a little extra protection. Ramuh summon and Bolt 2/3 is useful here along with enemy skill Trine if you have it. Cast M-Barrier to protect yourself from its Lapis Laser, which is quiet powerful. Do this and it should go down easily. You'll get Tifa's God hand for winning.
Once you've defeated this, the sub with the Huge Materia will have left the bay, so open the chests (there's no rush) and Hijack the other Sub. You'll need to chase the sub down so fight your way to the captains cabin in the Sub, you can wither fight the soldiers there or take them hostage. If you choose to fight them, steal from the captain for Shinra Alpha armour.
Now you'll be in control of the sub and will need to sink the enemy submarine, there will be a tutorial explaining the controls and about the other enemy ships that will attack you.
Square: Fire Torpedo Up: Descend
X: Slow Down Down: Ascend
Triangle: Speed Up Right: Turn right
R1: Sonar Left: Turn Left
Chase down and attack the red submarine because that's the one that has the Huge Materia. You'll have ten minuets to do this. Watch out for the small, funny shaped things near the towers because they're mines also try not to loose the Sub you’re pursuing because it can take a while to find it again. If you win you get to keep the Submarine. If you don't, don't worry because you can go back to Junon, follow the same route to the Submarine dock and hijack one easily. You'll receive a radio signal from the Shinra saying that the Huge Materia has been shipped from the Junon Airport, Dock and as you arrive you'll see a plane taking off, this has the huge materia on it. Now go back to Rocket Town.
If you haven't got the submarine, got back into Junon now and ride the elevator for 10gil again then head down to the submarine dock, you'll be able to hijack another sub there.