It has now been confirmed beyond any reasonable doubt that the South Korean Navy corvette Cheonan that exploded and sank on March 26 off the Korean coast was sunk by a torpedo fired from a North Korean Navy submarine. Not only does the damage to the recovered parts of the ship clearly show a powerful explosion beneath its keel, but torpedo parts have been recovered from the seabed where it sank that match known North Korean torpedo designs and carried markings in Korean. South Korean President Lee Myung-bak has pledged to take "stern action" against the North; the North Korean regime has rejected the claim as a "fabrication", and reportedly threatened war if sanctions are imposed.
The investigation was led by experts from the US, Australia, Britain and Sweden. The team examined eyewitness accounts, damage to the vessel, evidence collected from the seabed and the injuries sustained by survivors and those who died.
It said: "The evidence points overwhelmingly to the conclusion that the torpedo was fired by a North Korean submarine.
"There is no other plausible explanation."
Monitoring of seismic activity in the region, damage to the ship and the "fractures and lacerations" sustained by the dead crew were all consistent with "damage resulting from a shockwave and bubble effect" caused by an explosion directly beneath the vessel, it said.
The report said the torpedo parts found "perfectly match" a torpedo type that the North manufactures.
The ball is in South Korea's court now. China is calling for restraint from both sides, while Japan has denounced the sinking as "unforgiveable". (China prefers the more weaselly word "unfortunate".) North and South Korea remain technically at war, restrained only by the 1953 armistice, which North Korea has repeatedly tested the limits of (including periodic random artillery fire across the demilitarized zone, which South Korea has for the most part steadfastly ignored). North Korea officially unilaterally withdrew from the armistice on May 26 last year.
For myself, I have more than a passing suspicion that Kim Jong-Il is becoming desperate at the worsening internal situation in North Korea, with widespread starvation by many accounts. I suspect he may be actively trying to provoke South Korea into something he can declare internationally to be a casus belli and pretend, at least to himself, that it was South Korea that resumed active hostilities, so as to save face. The goal would presumably be to seize South Korea's resources in the hope of staving off collapse (which I expect would amount to shipping most of South Korea's food north, along with as much of its wealth as he could manage to loot, and letting the South starve instead).
I also suspect that if it came to a shooting war on the Korean peninsula again, China would do nothing to stop it unless and until it looked as though South Korea might win. See update below.
Japan would very likely act in support of South Korea; it's anybody's guess whether Congress and the White House would do anything beyond deploring and possibly putting North Korea back on the list of nations that support terrorism, which I'm sure will be a great deterrent to Glorious Leader Kim Jong-Il, who by most accounts is crazier than a sack of rabid stoats.
Updated:
Upon further consideration and excellent arguments here. as well as this assessment of internal DPRK politics, I consider it increasingly unlikely that China would get involved at all, under any circumstances, unless to step in and grab territory in the last stages of a North Korean defeat. I have little doubt that Kim Jong-Il believes that China would support North Korea again in a renewed military conflict, but when all the involved issues are taken into account including the economic relationship between China, South Korea, and the United States, and in particular the vast amount of Chinese credit in the Unites States, China has nothing to gain from a North Korean victory and everything to lose. (And in any case, there is strong cause to believe that in the event of an resumption of active hostilities, any North Korean military initiative would stall within a week for lack of food and fuel. Mass desertion from the North Korean army is also a very real possibility.) In particular, if a renewed Korean war were to break out and China were to enter it on the opposite side from the United States, it would be a complete no-brainer for the United States to both seize Chinese assets in the US and repudiate — with no international consequences — all US debt currently held by China. That would be a huge windfall for the US, and a huge blow to China.
The more I think about this, the more vanishingly unlikely it appears that China would enter a renewed war to assist North Korea. China literally cannot afford to get involved on the North Korean side. In fact, China's best move, beyond standing back with its hands folded urging restraint on all sides and offering to facilitate negotiations, might even be to come in on the side of South Korea "in the interest of peace in the region" and incidentally pick up some North Korean territory along the way.
It increasingly appears that this cannot end well for North Korea unless South Korea completely caves to North Korea's saber-rattling, which would be likely to have severe consequences for the current South Korean government and result in its replacement with a more hawkish administration. And in the long run, that would be bad for North Korea too. So I think what we have here is a no-win situation for North Korea.