This week, North Korea's dynastic leader, Kim Jong-un, was beaming from ear to ear as a Pukgeukseong-1 missile shot out of the water, apparently launched by a new "Sinpo" class strategic submarine. For Kim, Christmas arrived early.

The United States and South Korea publicly sneered at the missiles launch calling it a fake, a dummy, trick photography or a re-tread old Soviet SSN-6 missile. Washington has always underestimated North Korea ever since the Korean War of the 1950’s. South Korean intelligence has an entire department that routinely spreads phony stories about the North, like the canard that Kim had his uncle eaten by wild dogs.

But behind the scenes, there was real worry in both Washington and Seoul, and for a good reason. Even a few North Korean submarines equipped with underwater-launched ballistic missiles with nuclear warheads could pose a grave strategic challenge to the US, South Korea and Japan.

North Korea now has an estimated 10-20 small nuclear devices according to foreign intelligence estimates. Some of them are believed to be fitted to the North’s medium-ranged Rodong missiles pointed at South Korea, Japan and the major US Pacific base on Guam.

Pyongyang has been trying to develop a miniaturized nuclear warhead to fit atop its longer-ranged Taepong and a new ICBM under development. Recent tests of the extended-range missiles have been failures. But the North Koreans are quick learners and determined. However, they lag far behind in developing solid-fuel missiles, relying instead on cumbersome, vulnerable liquid-fueled missiles.

The US has the technological capability to intercept long-ranged ICBM fired from North Korea, and ample early warning time. However,it’s hard to imagine why the North would use its nuclear arms except in last-ditch self defense as the US would obliterate the North with retaliatory salvos of nuclear strikes. US forces in South Korea, Japan (Okinawa), Guam and at sea have stocks of tactical nuclear weapons.

But a North Korean sub lurking off the US East Coast could launch against Washington and New York with only minutes of early warning. American anti-submarines systems, like the upgraded SOSUS underwater hydrophone system or towed hydrophones, would likely pick up the North Korean subs, which are believed to be noisy, but there’s always a chance one or more could slip through, or launch out of range of underwater defenses.

South Korea has invested a great deal of money and effort into building what it calls a “kill chain” designed to attack North Korea’s short and medium-ranged missiles before they can be launched or during their initial boost phase. This system is based on drones, aircraft, radars and satellite linked to a central command. North Korean submarines could outflank South Korea’s strategic defense system.

But North Korea is not about to start a nuclear war of which it would be the principal victim. Pyongyang’s nukes have always had the primary role of warding off a US-South Korean invasion – an operation that the two allies practice every fall, producing violent tantrums from Pyongyang.

Kim Jong-un knows Iraq and Libya would not have been invaded if they had possessed nuclear weapons. Syria may be next on the western hit list. The Kim dynasty’s days would be numbered without its nuclear arsenal.

But the Kim monarchy is also beset by growing internal tensions. The 30-something Kim has been wrestling with his father’s old guard, a cadre of reactionary senior generals, party officials and influential relatives jealous of their power and wealth. The Swiss-educated Kim wants to bring change to stultified North Korea.

We must be cautious of news about North Korea, which is often outrageous nonsense that is dutifully parroted by western media without many questions. But there’s also no doubt that the Kim regime has abrupt, spasms of violence that suggest the young leader is both unsure of himself and under siege.

Last week’s outrage du jour concerned North Korea’s new defense minister, Hyon Yong Choi, who was arrested and then reportedly executed by one or more heavy, 12.7mm machine guns. His offense, it seems, was showing insufficient respect to Kim and even dozing off during a speech being given by the leader – a very sinister Stalinist touch to a traditional Korean flair.

Choi’s explosive execution comes after Kim had his uncle, Jang Song Thaek killed and eaten by wild dogs, according to a lurid fable spread by South Korean intelligences. There are so many wild stories spread about North Korea it’s hard to separate fact from fiction.

Young dictator Kim’s ambitions are upsetting the north Asian applecart. Japan feels naked before its Korean and Chinese foes and will feel pressure to rearm and break away from American tutelage. South Korea has the same problem, compounded by growing numbers of young South Koreans who believe Kim’s claims that the North, not the South, is the authentic Korea. Add the Chinese who are nervous about the unpredictable Kim and even Israel which fears he will arm their Arab and Iranian enemies.

No wonder the respect and attention-craving Kim Jong-un looks so happy.