The fused sensor picture
Eyes, radar, sonar, magnetic sensors and laser designators all feed one shared picture. Hills cast radar shadows, jammers blind whole sectors, and deep submarines hide from everything but sonar.
A combined-arms RTS where information is the main weapon. An enemy only exists for you while one of your radars, sonars, sensors or spotters actually holds it.

Every match is fought on a freshly generated island, archipelago or strait, 8 km across and ringed by open sea. Radar sees far but gives itself away. Night falls and your eyes go dark unless you brought thermal optics. The side with the better sensor picture wins the fight before it starts.