The adversaries tapping undersea cables are state actors operating extremely expensive kit.
The US did this in the Cold War as Operation Ivy Bells. A spy leaked this to the soviets who then retrieved a tap.
But it went on. Nowadays the US operates the USS Jimmy Carter and the Russians have a whole directorate, GUGI, operating a fleet of special submarines and surface ships.
I get your point but I wonder about “many”. Of the 532 cable runs, I wager that a cut cable is more impactful than traffic analysis. In USA, the specifics of eavesdropping even require that the origin of one side of the traffic is assumed or known.
The US did this in the Cold War as Operation Ivy Bells. A spy leaked this to the soviets who then retrieved a tap.
But it went on. Nowadays the US operates the USS Jimmy Carter and the Russians have a whole directorate, GUGI, operating a fleet of special submarines and surface ships.
Links: http://www.hisutton.com/Secret%20Sub%20-%20USS%20Halibut.htm...
http://www.hisutton.com/Undersea_Cables.html