Actually we used to have a lot more. We've mothballed and dismantled a lot of the systems since the Cold War. The North Atlantic used to be littered with SOSUS sensors and modified fishing boats (for stealthy radar profiles - fiberglass superstructures and such) that pulled SURTASS towed array sonar instead of fishing nets during the latter 70s into the 80s, because that's where the naval battles that would decide the fate of Europe would happen.
The shipping lanes determined where those pesky commie submarines that would attack the supply convoys would hunt. They called the chokepoint where Ivan would surge out into the Atlantic the G-I-UK Gap, for Greenland, Iceland, and the UK. If it happened, it would start there, so they focused a lot of sensors there. Shit, I first learned about this stuff reading Tom Clancy novels when I was in jr high school. It wasn't exactly hush-hush.
I should give Red Storm Rising another read...