The Sonar Station is a level 1 special naval tower that both the CORE and the ARM can build; it has no attack of its own, but can detect enemy ships and subs within its coverage even in unexplored areas and display them on the minimap. Enemies that are detected by sonar but are not seen visually will be displayed as "unidentified units", and any unit that can attack them must be manually ordered to do so unless a Targeting Facility is built.
The purpose of the Sonar Station is to detect submarines that may be in the area. Subs are always hidden unless they are in the range of a sonar.
The Sonar Station can locate units that travel underwater, and displays the information on the mini-map.