September 10, 2016:
In Britain the Royal Navy has found it impossible to attract enough qualified sailors to operate all its nuclear submarines, especially the SSBNs (nuclear powered subs carrying ballistic missiles). The reason is that SSBNs stay at sea for 90 days at a time wanting for a brief message to fire its missiles at pre-arranged targets. The problem is that too many otherwise qualified sailors and officers are not willing to spend 90 days without Internet access. This shortage has already reduced the number of days British SSBNs can spend at sea.
This problem is not easy to fix because submarines are so effective because they are difficult to find and attack. For that reason they rarely use two-way communications while submerged and something like the Internet requires sending and receiving a lot of data constantly.
The U.S. Navy has been working on a solution since the 1990s, so far without success. For example, in 2009 the Americans thought they could use lasers for communicating underwater. This was done by using a laser pulse tuned to ionize water and generate an acoustic pulse. Thus surface ships or aircraft could communicate with suitably equipped subs. This idea never got out of the lab, at least not yet. Given the need for underwater communications there's lots of incentive to get something like this into service. If that ever happened it would revolutionize submarine operations, not to mention solve a growing recruiting problem.
For years, researchers have been trying to find ways to use lasers to detect submarines, or to enable underwater communications. So far, it's been found that blue-green lasers can reach some ten meters beneath the surface, and be used for detection and communication. Not terribly useful for subs (which typically stay farther down than ten meters), although work continues on using this capability to search for bottom mines in shallow waters.
In 2007 the U.S. Navy completed development of Deep Siren, a system that enabled nuclear subs to communicate with the rest of the world while submerged at a great depth. This "tactical paging system" provided a practical solution to the problem of communicating with a submerged sub. The system consists of a disposable buoy that is dropped in the water, by an aircraft or over the side of a ship, in the general area (within about 90 kilometers) where the sub is believed to be. The buoy sends out an acoustic signal that U.S. subs are equipped to automatically pick up. This coded message either orders the sub to get a radio antenna above water and call home, or simply delivers a brief message. The buoy also has a satellite telephone capability, so that additional messages can be sent from anywhere, to the sub. The sub cannot send messages to the buoy (because powerful sensors are required to pick up the signals). In the past, the only way to "page" submerged subs was via a large, shore based, low frequency, transmission system. This system as reliable as a laser based one would be but had a much longer range. Something like Deep Siren does not solve the Royal Navy recruiting problem.
The U.S. Navy did successfully test the other end of the Deep Siren system. To do this, the sub released a similar buoy through its garbage chute. The buoy hovers for a while (so the sub can move away), then rises to the surface and sends its messages. Thus the buoy signal will not give away the exact location of the sub. The buoy then receives messages (short ones) and uses a sonar type device to send the data acoustically, for up to 90 kilometers, to the sub. Outgoing messages, which are sent via satellite, can be longer, and even include outgoing email from the crew to family. But the acoustically transmitted messages are much shorter, and include orders from the surface ships, or anyone in the chain of command, to the sub commander.
Deep Siren can also be useful for American carrier task forces, which are usually accompanied by at least one SSN (nuclear attack sub.) Because thermal layers make underwater transmissions vary a great deal in range, the buoy sends the command messages several times to insure at least one gets through. The buoy from the sub can stay active for several days, if the sub is remaining in the area. But eventually, the buoy sinks itself.
The U.S. Navy has spent about $10 million on Deep Siren to install it in some subs and test it. These tests continue, to see how reliable it would be under realistic conditions. The testing determined that Deep Siren wasn't ready for prime time yet, but for security reasons, details were not released.