On land in the digital age, it’s easy to take communications for granted. Images and videos are easily streamed on portable devices, the internet is wirelessly available more often than not, and finding an address only requires a GPS enabled smart phone. Once a few miles offshore though, everything changes. There are no wifi hotspots and there is no cellular network. In order for people or robots to communicate back to land, satellite communications are typically used. Satellite communications are typically more expensive and carry less data than typical land-based networks. Thus certain strategies must be employed by devices that are designed to operate. For instance, a mooring collecting high resolution water current data might use onboard processing to send just a summary back to shore while awaiting a higher speed link like a ship or surface robot to occasionally come close enough to allow for a full resolution data download. Once under the surface of the water, communications become even more difficult. Radio Frequency (RF) waves don’t propagate underwater so things like satellite modems or GPS receivers won’t work. A number of different communications techniques can be applied underwater using optical or electromagnetic sensors. By far the most common technique uses acoustic sound waves that are modulated to send data between modems much like early Hayes styles analog modems used with home computers. This style of communication is even more limiting in bandwidth and uses much more energy per byte than RF communications. Various acoustic techniques can be used to aid in navigation of mobile underwater platforms like autonomous underwater vehicles (AUVs) and moored platforms can make use of acoustic communications to send critical data up to the surface. For example a seismometer mounted on the seafloor can limit its communication to just seismic events of interest.