Somehow through 70 years of nuclear buildup we've managed to avoid complete annihilation or worse. No world leader has pushed the button or turned the key or made the call, no volleys of ICBMs have been launched from cornfield silos, no squadrons of bombers have taken off on one last nuclear-armed flight. We are alive, even though, as any reasonable alien observer might conclude, we should not be.
Some large part of this of course has to do with our old friend mutually assured destruction, or just MAD. If you obliterate us, we will obliterate you. Key to this is that each nuclear-armed nation partaking in the MAD standoff has the ability to retaliate should any other nation launch an attack, no matter what. This is known as second strike capability. Each nation knows that there is no first strike that can be launched that will prevent a second strike retaliation. It doesn't exist.
This second strike capability rests largely on fleets of nuclear submarines. The depths of Earth's oceans offer some spectacularly effective hiding places and it's here that our second strikes lurk silently. Your nation can nuke every square inch of mine, but there is not a whole lot that you can do about my hidden navy of death-shadows.
Technology is changing what used to be a nuclear deterrence given, however. As detailed in a new report in the Bulletin of the Atomic Scientists authored by naval strategist James R Holmes, navies are coming up with new ways of hunting even the deepest, most hidden submarines. Simply, no sub can run completely silently—owing at the very least to the swoosh of water around its hull—and so their unmasking is nearly inevitable given improving listening technology. And, indeed, that tech has improved to the point where once ghostly submarines have become fair game for detection and, if neccessary, elimination.
There are a number of new technologies being developed to this end, according to the Bulletin paper. "The Distributed Agile Submarine Hunting program, to name one, will strew 'deep-ocean sonar nodes' across broad areas of seafloor," Holmes writes. "Deployment remains some way off, but these sonar nodes, or 'subullites,' would be equipped with a wide field of view in order to gaze upward to detect and track subs passing overhead."
"Anti-sub technology will have reduced Kissinger's first variable, power—and deterrence along with it"
So far, engineers have built one node-based prototype and it's expected that eventually these arrays of nodes will be deployed across vast reaches of the ocean. A second component of a future sub detection net may come in the form of an under-development unmanned undersea craft known as the Submarine Hold at RisK, or "SHARK." Once a sub is detected, it will be the SHARK's job to silently stalk it, reporting its findings back to human commanders. Escalation being escalation, we can expect that Russia and China are working on similar tech.
"If so, the wine-dark sea will become transparent to sub-hunters for the first time," Holmes frets. "No longer will attack subs be able to form picket lines, awaiting foes closing in from afar. No longer will attack boats be able to assail enemy subs or surface vessels, or bombard hostile shores, without fear of retribution. And no longer will ballistic-missile subs vanish into opaque patrol grounds, immune to detection, to mount the threat of atomic devastation. In short, anti-sub technology will have reduced Kissinger's first variable, power—and deterrence along with it."
Generally, things can go two ways from here, according to Holmes. If nuclear powers roughly keep pace with each in developing this sort of technology, nuclear deterrence should remain much that same as ever, but if one nation gets out ahead, then things become shaky. The powers without the tech become anxious, while those with it feel pressured to use their "decapitation strike" advantage while they have it. In other words, there is a risk to becoming too good at this stuff.
"Succeeding too big in offensive and defensive submarine warfare could give rise to a first-strike psychology that primes opponents to hit first or launch at the first suspicion of an attack," Holmes concludes. "Upsetting the undersea nuclear balance is therefore something Washington should undertake only after ample forethought. That's something to ponder, especially during an election year."