The tactical view (also commonly known as the Sonar) is available by pressing spacebar while using the periscope. In this view you can see an extended area, reaching from one side of the map to the other. The view updates in bursts, and is not smooth like the periscope and you do not need to allocate power to lights to be able to see with the Tactical View, making it particularly useful in dark biomes. Aditionally, you will also be able to see the amount of power in each console, as well as the amount of fuel you have, your total torpedo count, and the number of torpedoes currently loaded into Torpedo Tubes.
The tactical view can be used to scout ahead and inform the gunner and driver about the position of enemies, caves and where to go, which makes it particularly useful when faced with branching paths, as it's usually needed to know which way contains a cave or an Undersea Lair. This job is tipically reserved to the Engineer.