When an Aegis destroyer should reveal itself by radar

How do Aegis destroyers decide when to activate radar without advertising the task group's position?

They can rely on airborne warning such as Hawkeye, but in a sufficiently dangerous environment the need for a clear picture overrides emissions control.

A Hawkeye airborne early-warning aircraft can provide warning while the surface ships manage their own radar emissions. Whether an Aegis destroyer should transmit still depends on the situation. In a sufficiently threatening environment, obtaining the information needed to understand the danger takes priority over avoiding detection. No universal activation rule is given.