re: Security question regarding possible attacks on US mainland

We have sub detection cables laid off both coasts and through the Gulf. Basically giant magnetometers. Not a secret at all. They were laid in the late 50's and early 60's. Friends dad was in the Navy and did this. The system will pick up a big sub but not the narco "subs" because those aren't actually subs. They are primarily fiberglass craft that run with about 90% of the craft below water but the top sticks out for navigation and ventilation. They are low enough in the water to not have a radar signature but aren't actually submarines.