North Korea's nuclear and missile programs continue apace. In the last few days, the North has tested a submarine-launched ballistic missile (SLBM). Specifically, it was an 'ejection test' to see if the missile's propulsion was strong enough to break the surface of the water (it was).

North Korea is on its way to an 'assured second strike' capability — SLBMs can survive even a massive first strike by an opponent and allow the attacked state to respond with nuclear force. SLBMs also offer greater range. North Korea has worked on an intercontinental ballistic missile (ICBM) but has struggled with multi-stage rockets that could actually traverse the atmosphere at great distance. A North Korean submarine on station off the continental US would not need long-range missiles to bring most US cities within range.

I see three medium-term consequences to this SLBM evolution:

1. It will drive American paranoia over North Korea to new heights

American cities have thus far been exempted from the North Korean missile threat that looms over Japan and South Korea. So SLBM development does little to change their threat perception and strategic situation. Instead, these SLBMs are clearly pointed at the US. They improve Northern deterrence by signaling that American cities will suffer retaliation if 'regime change' is tried. (NB: the Pentagon claims North Korea already has an operational ICBM but South Korean officials reject that.)

But I do not think the North realises how much this will push America toward even more hawkish positions. SLBM deployment would almost certainly lead to more sanctions and the accelerated pursuit of North Korean money in Asian banks. The US will also accelerate missile defense development and arm-twist South Korea on the Terminal High Altitude Area Defense (THAAD) system. And it will push the American defence debate to the right and help ultrahawkish GOP presidential contenders.

Is this really what Pyongyang wants? Do they really want John Bolton working for another White House?

2. It will encourage South Korean missile-defence development

SLBMs will also push the THAAD debate in South Korea toward deployment, yet another unintended consequence for Pyongyang. The South Korean left has managed to forestall THAAD so far, in part by arguing that North Korea is unnecessarily provoked by South Korean and American hawkishness. But SLBMs weaken that position.

At the outermost limits of rationality, one might argue that North Korea could objectively want some nuclear weapons, given the American dalliance with regime change, and how far behind Pyongyang is in conventional military power. But even by that generous standard, there is no defensible reason for North Korea to seek ICBMs, SLBMs, dozens or even hundreds of warheads, and so on. Even Beijing sees this. And now, if North Korea's nuclear weapons are immune from pre-emptive strikes because they are underwater and impossible to find, then the debate on missile defence in South Korea has essentially been won by the hawks.

3. It may prompt Seoul to think about pre-emptive strikes

Elsewhere I have argued that North Korea's spiraling nuclear and missile programs would slowly push Seoul toward pre-emption. I have long thought that a South Korea without a missile defence 'roof' or its own nuclear weapons would feel acutely vulnerable to North Korean nuclear missiles. And just as the Americans considered preemptive air strikes on Soviet missiles in Cuba in 1962 before they became operational, or as Israel did in Iraq (1981) and Syria (2007), so I imagine a rising temptation in South Korea to strike before the Northern program really gets out of hand, with hundreds of missiles and warheads.

SLBMs change this in two ways. First, if North Korea can actually deploy them reliably, then the value of preemptive strikes declines dramatically. Under-sea launchers cannot be targeted for preemption; that is the whole point of SLBMs. At that point, missile defence is the only possible strategic response, and one can foresee an accelerating missile vs missile-defence technological race among the two Koreas and the US.

A second, more frightening prospect is that SLBMs set a timeframe on the North's vulnerability to air strikes. A closing window of opportunity might therefore encourage Southern air action sooner (as was the logic of Germany in 1914; it believed that it could not defeat Russia once Moscow's western rail system was completed).

Increasingly, I cannot see how this ends well. No matter the consequences, the North seems hell-bent on hugely threatening nuclear deployments that will only further entrench hawkish, confrontational elites in South Korea, Japan, and the US.