What Ben showed Sawyer could always have been an illusion, but assuming it’s real, I am now left with further questions regarding the underwater hatch.
When many of us first suspected that an underwater hatch existed, we did so on the basis of two clues: the marked shark and the cable going out into the water.
If the view that Ben showed Sawyer is our island, and IF Jack’s tank (potential “underwater hatch”) is on (or directly offshore of) the same island that Kate & Sawyer are on (which I’m still not convinced of), then there is a huge question remaining: where does that cable go?
It clearly can’t go to the island that Ben & Sawyer were standing on, because if that were the case then Sayid (and anyone else who stumbled onto the cable) would have been able to see the other island from that beach (unless it is somehow masked from view).
This is what I think is happening.
They are on a smaller island, that’s why Ben showed Sawyer in the first place and Sawyer saw the short beach. I thought too it might have been an illusion but there is one big reason why I don’t believe that now…the “submarine” and the need for the boat.
You could say that Walt and his Dad were directed to the small island, and that small island is the way out. I’d wonder what heading ben told Walt’s dad last season because if it’s north it correlated with the Jesus stick on Ecko.
I aslo don’t think they are underwater. I think Jack is just under a big tank of water. Maybe for supply maybe for a whale or shark tank. I’d love for them to be underwater but it’s unlikely since it’s in walking distance of the cages.
I think it’s pretty likely that wherever Jack is he is underwater.
1) For all that water to rush in when the door opened would not make sense otherwise. If he’s just under a big tank of water, then why would they have it rigged to flood in like that when the door is opened? If it’s underwater then it makes sense, since the series of doors would be an airlock that they could use to fill certain rooms for examination / experiments while leaving air in others.
2) It wouldn’t be practical to have a room equipped to examine large fish (like that one is) on dry land, because then you’d have to transport the animals there; it would be too difficult without heavy equipment which the scientists would be very unlikely to have on a remote island facility.
3) We have NO idea how close Jack’s room is in relation to the cages, because they’ve never shown anyone walk from one point to the other. Sure, lots of people (including the three hostages) go back and forth, but it could have taken them quite a while, or they could even have used transportation (underground train tracks connecting various “hatches”, etc.)
Or a simpler explanation is that it’s just a really long walk that they never fully show, just like the distance between the beach and the ex-hatch in season 2 - people went back and forth all the time and they rarely showed the journey, just people left the beach and they would be in the hatch on the next scene. I don’t see any reason to believe that this would be different.
UPDATE - Actually, now that I think about it, it could still easily be close enough to the water even for a short walk. Kate walked to and from the beach in the first episode of season 3, so there you go.
As for the submarine, I just took that as they wanted to use it to sneak up on them (the other boat) without letting the Losties see them coming.
Assuming there really are two islands, I highly doubt they take boats between them. I think they would have an underground/underwater tunnel with a built in transportation system that connects the two islands and all the various hatches, as hinted at on the map.