North Korea has the ability to prepare mobile ballistic missiles for launch under the cover of mountain hangars:
Recently the satellite photos revealed considerable previously undetected construction underground. There are apparently facilities down there, out of sight, for assembly and fueling of large (ICBMs or satellite launcher) rockets. The latest satellite photos showed construction of rail lines in the base that are extensive enough to handle moving an assembled rockets from underground assembly areas and into position for firing. What this all means is that North Korea can carry out launches with little advance warning. When the rocket assembly and fueling took place above ground satellite photos gave weeks of warning. Now a rocket can be brought out and placed in launch position within a few days. ...
[The] SDB also has a hard steel, ground penetrating, front end that can penetrate nearly two meters (six feet) of concrete. Not much use for that in urban warfare. But such a capability is very useful for taking out underground installations, particularly the entrances and air intakes. North Korea, for example, has twenty airfields with underground hangars for the aircraft. Usually tunneled into a nearby hill or mountain, the underground hangar allows fighters and bombers to quickly taxi out onto the runways and take off. Since North Korea doesn't have that many operational warplanes, it's believed that some of these "airfields" actually have long range rockets and ballistic missiles, mounted on trailers equipped to erect the missile into launch position and fire it off, in the underground hangars. The trailers are hauled out of the tunnels, onto the air field, the missile fired, and then the trailer is taken back inside to be reloaded. The North Koreans also have hundreds of other, smaller, underground facilities, close to the South Korea border, containing artillery and rocket launchers. These weapons are meant to be quickly hauled out and fired south.
This capability would come in handy if North Korea builds and hosts Iran's nuclear deterrent until Iran can build their own nuclear deterrent inside Iran.
Which might explain recent increases in North Korean Uranium and Plutonium production.
Of course, North Korea has a cover story for building more nukes for Iran. They're nuts and think we are a threat:
North Korea announced Tuesday that it has restarted its Yongbyon nuclear reactor and was ready to use nuclear weapons “any time” against the United States.
The announcement came less than a day after North Korea said it was preparing to launch a long-range rocket.
And Iran would definitely get their own in-house nuclear arsenal as soon as they can given all the SDBs (small diameter bombs) we've stockpiled and given the uncertain lifespan of the Kim regime.
Say, Iran unexpectedly discovered they have lots of Uranium, recall.