The article notes that in the early 19 sixties, nuclear powered submarines began to emerge. And these are like very, very quiet submarines, very hard to detect with radar and active sonar am so there's very, very little out there to detect it. But they still emit on some kind of very low frequency noises that can be picked up from far away by various networks. It costs about two point eight billion dollars for each of these nuclear powered submarines, according to the us Congressional budget office.