From: Upstate New York USA
For most scenarios, the parent default posture is set to "Radar Active." Scenario authors may change that for air and surface units, but I've found that they don't pay attention to subs since they are designed to be under water. This results in your situation. If you reset the posture to Radar Passive at the beginning of the scenario, this shouldn't be a problem.
I just ran into this recently when playing Tee Up. In 5000 square miles of ocean, I managed to drive my sub across the one shoal where the water is 2 meters deep. When the sub surfaced, they turned on their radars immediately. Nuclear subs, no less.
"It's all according to how your boogaloo situation stands, you understand."
Formerly known as Colonel Mustard, before I got Slitherine Syndrome.