Why can't Theater Defense Systems detect ships using their radar?
Unless ships and other units in real life have their radar turned off, they can be detected and localized by enemy units. I'm not suggesting that TDS be able to engage and destroy ships, but they should probably know that there's a naval vessel out there.
To expand upon this, why not make everything that's equipped with radar and not stealth/low RCS able to detect everything else that has radar?