Now that all DHARMA members on the Island are dead, the jamming is keeping DHARMA from sending more people to the Island.
I'm very sure that if you did not hear from your remote island research facility that has a long running problem with violent natives in nearly 2 decades, you might get a little concerned.
The Looking Glass station represents one end of a link between The Island and the outside world discovered and utilized by the DHARMA Initiative, with the other end being The Lamp Post station in LA. The names of the stations share similar symbolism from works of literature. Both stations sit over similar pockets of energy, which are anchor points on the ley line network, with The Looking Glass located at the point where the network intersects the local spacetime of The Island. It used the energy at that underwater location to provide an amplified target for The Lamp Post to track, allowing the location of The Island to be reliably predicted farther into the future than is possible without it, as was the case when The Lamp Post was first built, and when Eloise uses it to help the Oceanic 6. The longer timeframe is necessary to allow for a submarine to travel to the predicted location, and without The Looking Glass the location can only be predicted far enough ahead for The Island to be reached by aircraft. This location at a ley line network terminus also provides a means of overcoming the obstacle that the altered local spacetime presents to realtime communication with the outside world. This capability was seen when Ben showed Juliet live video shot by Richard. The Looking Glass also provides the sonar beacon for submarines, but it is only active for the minumum time necessary for the submarine to find it at the exact moment predicted by The Lamp Post and adjusted for local spacetime, so as to minimize the risk of detection by an unintended submarine. The Looking Glass does not jam communication or obscure The Island from the outside world, it does the exact opposite, makes both communication and finding the Island easier, simply ceasing to provide these functions effectively but not entirely cuts communication and hides The Island.
The Looking Glass not only jams the radio signals, but it forms a mirror bubble around the Island that is "painted" with the view of the ocean thus concealing the Island from any rescue attempts.
The Looking Glass refers to the facility as a reverse fish aquarium where DHARMA researchers would look through the walls of the plastic/glass tube to make scientific observations.
This station brings people to and from the Island through a portal of sorts. The sub docks in the moon pool, gets hoisted out of the water, and the journey begins. For Juliet's ride she was only asleep for an hour or so, and the "bumpy ride" was literally the whole ride. This also explains why Ben would tell Juliet it was flooded, he doesn't want her to know they got to the Island through the Looking Glass.
The Looking Glass is station "C4" on the blast door map. Its purpose is "Cryptography, and Communications Analysis". Through DHARMAtel connections to the Flame, radio tower and other island resources, and using its own equipment it can: jam,scramble/encrypt,intercept/block/route, and monitor communications locally and to the outside world as needed. Its underwater location helps it to block the magnetic disturbances caused by the nearby mountains, evade local detection and act as the guidance beacon for the submarine. After the discharge, under Ben's orders, the LG began to disrupt communications - but he lied to his people blaming the discharge.
"C4" is from "C4I" meaning "Command, Control, Communications, Computers, Intelligence;" the "4" was at one time a superscript and possibly before that a subscript, but it was easier to type "C4I" than stop to select the special character. Based on this, the Looking Glass was the real headquarters of the DHARMA Inititive on the Island. Newcomers arrived at the Island near the Barracks because they did not have a need to know about the Looking Glass.--Jim 08:51, 8 May 2008 (PDT)
The Looking Glass previously allowed entry to the Island because it was where the transponder that allowed the sub to find the Island was located and maintained before the destruction of the Swan damaged it. Ben may have told the Others that it was flooded to deter attempts to repair the transponder, because he wants to island to remain hidden.
The Looking Glass allows those on the island to view into the past of the outside world. Just as light is "slowed" (at least from our perpective) ever so slightly when passing through water, if there was a way to slow light to a much more significant degree, what you would be seeing could actually be hours, days, months, or even years in the past.
The cable on the beach is actually the anchor, seen in the schematic, and is used to tether the station to shore.
In the schematics, the station is clearly anchored to the sea floor by large pylons.
The cable keeps the Looking Glass Station attached to the island, so that when the island moves, the station moves with it.
On the schematic, diagram "C" shows the cable/anchor running to an exposed box on the beach, yet the cable that the Losties are familiar with runs up the beach into the jungle some distance and then goes straight under ground. We have never seen the power box shown on the Looking Glass Hatch schematic.
The cable runs to the tower, which may be located at the best place on the Island for communications. By the way, the best place is not necessarily the highest place.
In "The Long Con", Sayid and Hurley use a radio found in The Arrow to pick up signals, which were supposedly being blocked by the station, indicating it is spotty in its jamming. They picked up WXR radio.
Ben may have started jamming signals after the Hatch implosion when the Island became briefly visible. Tom said that communications went out after "the sky turned purple". Ben later admitted to jamming communications to Mikhail.
The security code in The Looking Glass is programmed by Hugo in the seventies. He knows one day Charlie will use the code, so he programs it to music.
One of the members of Geronimo Jackson, which likely included members of the DHARMA Initiative and were on the Island, programmed the code.
The time on the face of the clock in the Looking Glass logo is 8:15, which suggests a connection to Oceanic Flight 815, the plane that the survivors crashed in.
The two DHARMA logos are different because there are two Looking Glass stations in two different locations. A "Black" one and a "White" one. The one Charlie swam into is not the one represented on Sayid's diagram.
The Looking Glass is one of the unknown or crossed out stations on the blast door map. Kelvin and Radzinsky might have received knowledge of its "flooding", declared it a lost cause and crossed it off. The other possibility for the crossed off station could be The Door, due to its questionable nature as a real DHARMA facility.
The name of the station is a metaphor for the experience of coming to the Island. If, as is suggested above, The Looking Glass obscures the view of the Island from the outside world, arriving on the Island is literally "going through the looking glass."
What would actually happen
When the porthole breaks, air will start to rush out into the sea, with some violence and a good deal of noise. The air pressure exceeds the water pressure at the porthole by an amount proportional to the height of the porthole above the moon pool water surface. This appears to be about 2.4 m (8 ft) and the overpressure will be 0.24 atmospheres (about 3.5 PSI). Even though Charlie has already closed the control room door, the air in the control room retains this overpressure until the porthole breaks. The air then rushes out into the sea and within a couple of seconds, its pressure reduces to match the water pressure at the porthole. The air will now escape more slowly in great big bubbles, and gulps of water will slosh in between bubbles, just as happens when you push an open empty bottle horizontally into a sink full of water. It will take more than just a few seconds for the room to fill up with water, but it can't fill above the top of the porthole. Charlie can stand on tip-toe or float up with the rising water and breathe the large pocket of air above it, which will last him maybe an hour, while Desmond works out how to get him out of there, assuming Charlie's not quite skinny enough to swim out through the broken porthole.
It would seem intuitive that the weight of water in the control room would force the control room door open if Charlie undoes the latches on the inside. But the air pressure in the submarine port holding the door shut will still be greater than the pressure of the water on the inside, because the former is created by a greater total depth of water (i.e. depth of the moon pool surface below sea level). The pressure difference on either side of the door is proportional to the difference in height between the moon pool surface and the mid-point of the door, probably about 2 m (6 ft). It's equal to a 2 m / 6 ft head of water, which is quite a lot, and the two of them couldn't push and pull it open against that much pressure, which produces 2000 kg-force on the door if it's 1 square meter in area. If Charlie ducks underwater and undoes the latches and if Desmond can find something like a long length of strong steel pipe to use as lever, he may be able to lever open the door just a crack. A better solution is to use one of the firearms to shoot a hole in the door's porthole. Air will rush into the control room increasing the size of Charlie's air bubble up near the ceiling, then it will start bubbling out of the broken porthole again. The moon pool level will rise up and when it reaches half-way up the control room door, the pressure on either side of it balances and the door can swing open. Again, the water level in the main chamber can't rise higher than the top of the broken porthole. They have about a 12 foot space in the submarine port above this to breathe and prepare for the ascent. They need to get the diving gear, not only to assist with breathing on the swim out and the ascent, but because the Looking Glass is deep enough that, like divers, they ought to stop every 10 m on the ascent to clear nitrogen from the blood, or they risk suffering the bends.
The Looking Glass was originally above-water
This is clear by looking at the exterior in Greatest Hits.
Was it not on those stilts designed for it to be under-water like under-water oil mines. Also the outside looks like it was designed almost like a submarine to me.