North Korea has promised to destroy those speakers with artillery shells. A thousand mainly elderly South Koreans gathered to demand tougher retaliation and newspaper front pages are carrying stories about what message the Chinese Premier, Wen Jiabao, might have carried with him to Seoul late yesterday. But the heat is already dying down south of the 38th parallel. ''Some people worry about war,'' says Sunyoung Lee, a 43-year-old photographer in Seoul. ''But North Korea doesn't have money, they cannot do it.''

While many residents in the South have numbed to the tantrums of their northern neighbours, this one has a new deadly edge. Sinking the Cheonon is the North's first major conventional attack on the South since the late 1960s, marking a major shift in the North's risk calculus.

''It does seem to be a very calculated attack,'' Peter Hayes, the executive director of the Nautilus Institute for Security and Sustainable Development, says. ''Given Kim Jong-il is acutely aware that his conventional warfare capability is inferior in almost every respect, it shows that he thinks his nuclear capability can now compensate.''

During much of the Cold War North Korea's economy and military capability were stronger than the South and it could assume protection from China or the former Soviet Union. But the Soviet Union backed away from Pyongyang in the 1980s and then collapsed, throwing its Stalinist satellite into a new era of strategic vulnerability. Analysts say North Korea began developing its nuclear ''deterrent'' as its capacity to inflict unacceptable casualties through conventional means diminished.

Pyongyang agreed to Bill Clinton's 1994 request to cease its nuclear program when faced with significant inducements and a real threat of American attack. Kim Jong-il now appears to have correctly calculated that his adversaries are divided, their will for war is low and they will not risk a nuclear reply to an attack on the North. The US Secretary of State, Hillary Clinton, promised in Seoul this week to work with South Korea to chart a course to the United Nations Security Council, which is little different from ineffective US responses to previous provocations from Pyongyang. If the US is struggling to provide direction, then so too is China.