(Original post by Tempest II)
The DPRK's missiles aren't a threat yet. But once they are able to fit a nuclear weapon onto a missile then that probably changes
The point is that the Pukguksong-2 missile which they tested this month really constituted the delivery part of creating a credible nuclear weapons system, mainly because it is solid-fueled.
In the past they developed liquid-fueled rockets, but because you have to fuel liquid-fueled rockets before launch, during that fueling process they are extremely vulnerable to counterstrike. It's a slow and laborious process. But solid-fueled rockets are simply built and then they can be sealed up for years, waiting for launch. No need to fuel; you've built the fuel into the rocket when it is manufactured.
Solid-fueled rockets are much sturdier and more mobile than liquid-fueled rockets so you can place them on a TEL vehicle and drive them out into the countryside, moving them around almost like a land-version of what we do with our SLBMs (moving them around under the ocean to keep them safe). So Pukguksong-2, being solid-fueled and the NK's having developed a TEL and mastered 'cold launch', really have mastered the delivery vehicle (at least the missile part) of a credible nuclear strike capability (and even a second-strike capability given solid-fueled rockets can be dispersed out into the countryside, do not need to be fueled for launch and can simply move around or sit tight waiting, for years, for the launch order).
On the question of the nuclear warhead, many observers believe the September 2016 test last year was where the North Koreans finally mastered a miniaturised warhead with sufficient yield (20 - 30 kilotons). Many people believe the 2006 and 2009 tests were essentially like the Trinity "Gadget" (basically a nuclear device on a test stand, not actually a warhead) but that the 2013 test was the first test of a warhead design. However, they were having trouble with "fizzles" (not getting a full yield). The Jan 2016 test was still a fairly small yield (7 to 10 kilotons) but that the September 2016 yield showed they had mastered a warhead design, probably a 'boosted' design by way of deteurium / tritium injection.
The long and short of it is that if they have mastered the physics package (the nuclear device) of sufficiently small size and low weight, and we know they have now mastered a mobile, reliable solid-fueled rocket design with TEL and cold launch, all they now need to do is design the warhead bus / re-entry vehicle in which they will place the physics package. I haven't seen any observer who claims they have done so, but if they have overcome the development of solid-fueled rockets and boosted fission nuclear devices, then it's certainly not outside their ken.
The solid-fueled Pukguksong-2, with the miniaturised physics package and eventual warhead bus or re-entry vehicle, provides them with something approximating an actual, credible nuclear capability. Now Pukguksong-2 probably only has a range in the 1,000km to 2,000km range. It's not an ICBM-range system. But that range provides them with coverage of all the targets that they might credibly want to hit (in South Korea and Japan). I'd say the Telegraph was right to call it a game-changer in terms of actual, credible nuclear capability in a way those rickety, multi-stage liquid-fueled Taepodongs and their "Gadget", test-stand style nuclear devices they possessed in the mid-2000s, never were.