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"A symphony of death." That's the chilling phrase that Kurt Campbell, who is now Assistant Secretary of State for East Asian and Pacific Affairs in the Obama Administration, once used to describe the likely outcome of any military encounter on the Korean peninsula between the U.S., its ally South Korea and their mutual enemy across the 38th parallel in the North. The possibility of war breaking out once again in Korea is so unthinkable that a lot of people in various military establishments — the Pentagon, South Korea's armed forces and China's People's Liberation Army — actually spend a lot of time thinking about it. The truce between North and South has lasted for 57 years, but a peace treaty has never been signed, and now, in the wake of the North's attack on a South Korean naval vessel — and the South's formal accusation that the Cheonan was sunk by a North Korean torpedo — tensions are at their highest level since 1994, when North Korea threatened to turn Seoul into a "sea of fire."

Seoul has already made it clear that it will not seek military retaliation, and Washington and Beijing have said all the right things about trying to ensure that "cooler heads" prevail, as China's State Councilor, Dai Bingguo, said in talks with U.S. Secretary of State Hillary Clinton in Beijing on Tuesday. But all concerned parties understand that at a moment of high tension, the possibility of hot war breaking out is not negligible.

How might a shooting war start? Defense analysts and military sources in Seoul and Washington agree that an outright, all-out attack by either side is unlikely. Even a nuclear armed North, a Seoul-based defense analyst says, "would not risk an all-out war because it would be the end of the regime. Period, full stop." But there are ways in which smaller skirmishes could break out, and if they aren't contained, they could conceivably lead to disaster. Here are three that are uppermost in defense planners' minds:

The West Sea Redux
The site of the crisis — what Koreans call the West Sea (the Yellow Sea to everyone else) — remains the most obvious danger zone. Prior to the March 26 sinking of the Cheonan, there had been three separate naval clashes in the past decade along the so-called Northern Limit Line. The NLL is the de facto boundary that was drawn in 1953 by the head of U.N. forces at the end of the Korean War. Some say the North has never recognized it; others claim that it implicitly did in a 1992 non-aggression pact signed with the South. With the sinking of the Cheonan — an obvious violation of the 1953 armistice — the West Sea is obviously the most sensitive flash point. After the sinking, South Korean President Lee Myung Bak said that North Korean commercial ships — including fishing vessels that hunt for blue crab in the summer months in the South's waters — could no longer venture below the NLL. Pyongyang responded by saying that, likewise, no ships from the South would be welcome north of the NLL. That means all sea-borne traffic from both sides needs to steer clear of the de facto border, lest "they get blown out of the water," says a Western diplomat in Seoul. "That by definition, under these circumstances, is a fraught situation, given that both sides are on a hair trigger now."

Loudspeakers at the DMZ
To much of the rest of the post–Cold War world, the idea seems slightly farcical: setting up big speakers on the southern side of the demilitarized zone and broadcasting — loudly — news and anti–North Korean propaganda across the border. To some it conjures up images straight out of Monty Python and the Holy Grail ("I fart in your general direction. Your mother was a hamster and your father smelt of elderberries"). But it's no joke. Cheong Seong-chang, senior fellow at the Sejong Institute, a think tank in Seoul, believes that South Korea's plan to restart these broadcasts will likely infuriate North Korea. "Their military is already in a high state of emotion," Cheong says. And indeed, North Korea has already said publicly that it will shoot at any speakers broadcasting from the southern side of the DMZ. The defense analyst in Seoul says that if Pyongyang were to follow through, it would be "a serious act of aggression, and South Korea must counter it."

Tit for Tat Getting Out of Hand
Shots fired across the DMZ at a time of such tension is a potential disaster waiting to happen. A senior U.S. diplomat concedes that these sorts of incidents "are not at all unlikely to occur" over the next weeks and months. "The key is not letting them escalate. Our side understands acutely the dangers of things getting out of hand." Complicating the situation is that, according to a former senior military official in Seoul, the South Korean government will in all likelihood respond in kind to any future military attack from the North. "We will not do anything in response to the Cheonan [militarily], but I do not expect that that would be the case in any future incidents," says the former official.

The question is, Does North Korea know that, and if not, how to communciate the message? There is no hot line between Seoul and Pyongyang, and North Korea announced on Wednesday that it was shutting down a phone line run by the Red Cross in Panmunjom, the so-called truce village set up by the 1953 armistice. The danger here is obvious. The only open lines of communication are two that are affiliated with the train links between the Koreas (including a route to the Kaesong Industrial Zone, which the North has threatened to close). The only way now to get a message to the North about what the South will not tolerate going forward may be via the Chinese. Conveniently, China's Prime Minister, Wen Jiabao, will head to Seoul on Friday for talks with Lee. North Korea will dominate that discussion. Let's hope they figure out how to keep Pyongyang in the loop.

— With reporting by Stephen Kim / Seoul

• Bill Powell
• Military retaliation for the 'Cheonan' incident is unlikely. But the possibility of war breaking out between North and South Korea is not negligible. Here are three scenarios