On Metal Gear Solid,after you found the Darpa Chief/Decoy Octopus,you go to the elevator and go to B3.and knock on the wall.When you find a diffrent sound by knocking on the wall you blow it up with C4's.Then you go all the way down that room and do the same thing.then you go all the way back there and there is two more hidden doors when you go to the right one you will find Revolver Ocelot,kill him.