[jcrawfordor]

Historically the hydrophones were attached to cables that were laid using AT&T cable-laying vessels, so technology extremely similar to the transoceanic cables of the time (thus AT&T's involvement). The change to IUSS added the ability of mobile sensors to report into this system, so there's apparently something available there (I would assume satellite). We also know that the Navy possesses buoys that trail hydrophones, and I would assume these can be integrated into IUSS as well. The modern details get to be classified though.

As I understand it most of the original SOSUS arrays are still in operation, but I think they're more useful for scientific research than submarine surveillance at this point just because the newer arrays are much more sensitive. The locations of the original SOSUS arrays aren't totally public but you can put together some pretty good inferences about a lot of them, for example based on the NAVFACs that had similar cover stories and then closed at around the same time. Each one would have been the landing station and control point for a '60s array.