After Sayid explodes, everyone is thrown around in the submarine. Frank gets up off of the floor of the control room and moves towards the rest of the group. He stops at the hatch window which has started to leak water. He says "Ah, hell" then the hatch is thrust forward and he is knocked unconscious as the water rises. He is likely dead.
Jack sees Kate in the rising water and pulls her out. Sawyer grabs Hurley who is okay and Sun is pinned against a wall by a large metal box. As Sawyer goes to help Jin free Sun, Jack tells Hurley to get Kate out of there and he'll take care of everybody else. Hurley says that he has to help Sayid and Jack says "There is no Sayid!" Jack gives Hurley an oxygen tank and tells him to take Kate though the blast hole in the side of the submarine. He tells Hurley that he can do it.
As the sub sinks, Hurley and Kate make it to the blast hole as Jack goes to help Sawyer and Jin. They manage to move the large metal box, but then they realize that Sun is still trapped by some mangled metal beams.
As the sub shifts suddenly, Sawyer is knocked by some falling wreckage. Jin continues to struggle with the metal trapping Sun as Jack pulls Sawyer out of the water. Sun tells Jin to leave, but he says he's going to get her out. Jin tells Jack to get Sawyer out and refuses an oxygen tank that Jack offers him.
Jack shares parting, mournful looks with Sun and Jin, then makes his way out of the submarine with Sawyer.
Sun and Jin certainly deserve their own post, so you'll see that coming up next.