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U.S. soldiers prepare for a military exercise near the border between South and North Korea on April 14, 2017, in Paju, South Korea.Chung Sung-Jun/Getty Images

The diplomacy of aerial bombardment seems simple enough. Fire a few dozen missiles at an air base, or drop an enormous bomb on a cave complex. Then, watch your opponents cower at your fearsome display of power.

So why not try the same with North Korea?

For decades, the United States has crafted detailed operations plans that specify targets and timelines for armed assault on a country whose pursuit of nuclear-tipped long-range missiles has terrified generals and presidents alike.

Read more: China says North Korea tension has to be stopped before 'irreversible' stage

Since Donald Trump's arrival to power, the White House has expended fresh energy on mulling a military option in North Korea. The President has delivered a clear message that he is willing to use force against adversaries through his strikes against Syria and Afghanistan.

Mr. Trump's administration has inferred a similar threat against North Korea, dispatching an aircraft carrier group toward the Korean peninsula that Mr. Trump called an "armada" supplemented by submarines. Secretary of State Rex Tillerson has said "all of the options are on the table" in confronting Pyongyang's nuclear program.

On Friday, Chinese Foreign Minister Wang Yi further warned that "conflict could break out at any moment."

Since the end of the Korean War, no U.S. president has authorized an attack on North Korea, even when Pyongyang killed U.S. soldiers, captured a spy ship, shot down an airplane and sank a South Korean warship.

Now, however, North Korea is nearing completion of a program to develop a miniaturized nuclear bomb that can be fitted on an intercontinental ballistic missile and threaten the continental U.S. Satellite imagery suggests Pyongyang is preparing for another nuclear test, its sixth, and one Washington wants to keep from taking place.

But the options that exist for military strikes illuminate the difficulty of seeking a solution with bombs, particularly if Mr. Trump wants to avoid sparking a dangerous conflagration.

Any pre-emptive U.S. strike would likely seek to disrupt North Korean nuclear capabilities, so "testing facilities in the north of the country would be the targets. That seems obvious," said Robert Kelly, an expert on security in Northeast Asia at Pusan National University. "Probably ports, too," he said, in hopes of targeting a North Korean submarine that could be used to launch ballistic missiles.

"Ports are also important for proliferation concerns. The real trick would likely be road-mobile launchers. If North Korea really has them, as it is has also threatened over the years, then allied air power would have to hunt them all over the country conceivably."

U.S. forces could target Yongbyon, where North Korea has a nuclear reactor complex and reprocessing plant used to manufacture plutonium for weapons.

They could also launch attacks on North Korean uranium mining facilities.

Such a strike by the United States would almost certainly involve conventional weapons – not nuclear arms – and involve "co-ordinated precision air strikes coupled with special forces action intent on disabling key launch facilities and command and controls nodes," said John Blaxland, acting head of the Strategic and Defence Studies Centre, at Australian National University.

But the very act of designing a target list also quickly exposes the problems in engineering a military end to Pyongyang's nuclear ambitions.

North Korea is roughly 70 per cent forest and mountain, complicating aerial surveillance, and fear of U.S. air strikes has led to decades-long tunnelling efforts, Prof. Kelly said.

"They likely have a lot of stuff underground and would move more there once the bombs start falling. So an air campaign would likely take a while," he said. And "once it starts, they would also likely use human shields."

Experts on North Korea doubt the United States has sufficient information to know exactly when a nuclear test would begin, raising doubts about its ability to strike pre-emptively to prevent such a test.

There are questions, too, whether it's wise to fire at anything that contains nuclear material, given the potential for radioactive fallout to spread to nearby South Korea and China.

That's if North Korea's most prized assets, its small arsenal of existing nuclear bombs – perhaps two dozen at most – can even be found, which is by no means certain.

"We don't know where their nuclear weapons are," said Joel Wit, a senior fellow at the U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies.

So even in a direct attack on North Korea's atomic weapons capability, "your chances of success, whatever that means, are not that great," said Mr. Wit, whose background includes advising the U.S. government on resolving North Korea's weapons program and devising nuclear non-proliferation policy. "You might set the program back somewhat, but I think the majority of North Korea's key facilities, and certainly their nuclear weapons, would remain untouched."

It would be very easy for a limited strike to expand to something much larger, and "then you're into full-scale war when you do that," Mr. Wit said. "So it's a losing proposition, unless you are willing to accept the possibility of a second Korean war."

That's in part because North Korea has a potent ability to return fire.

Pyongyang wields enough artillery and rocket might that "the northern portion of Seoul could be saturated with fire," Austin, Tex.-based geopolitical analysis firm Stratfor found in a January evaluation of North Korea's reprisal options. Using rocket launchers alone, a single co-ordinated "volley could deliver more than 350 metric tons of explosives across the South Korean capital, roughly the same amount of ordnance dropped by 11 B-52 bombers."

Seoul is home to 10.2 million people, and its city limits are less than 60 kilometres from the border with North Korea. Though it is a city built to defend against attack – subway stations are equipped with gas masks and thousands of underground shelters can accommodate at least twice the local population – the loss of life would almost certainly be horrific.

In addition, Stratfor estimates that North Korea possesses more than 1,000 ballistic missiles, enough to rain down 1,000 metric tons of high explosives on South Korea, Japan and U.S. military installations.

"There is no way any pre-emptive attack could prevent such retaliation. The North could use aircraft, ships, missiles, artillery or ground forces to strike at Seoul and even further south, killing and destroying more than whatever a limited pre-emptive strike could achieve," said Dennis Blasko, a former military intelligence officer who was posted to Beijing and has served in the Defense Intelligence Agency.

For that reason, some Korean observers believe the only real way to use weapons against Pyongyang is a full-scale assault.

"If the military option is to be considered seriously, it has to be not in a limited sense, but to make sure that North Korea is completely decapitated in terms of the command structure, where it will not be able to retaliate," said Jung Hoon Lee, an expert in North Korean nuclear history who is director of the Institute of Modern Korean Studies Yonsei University.

"That's not a small show of force, no. But who thinks that a small show of force would actually lead to the denuclearization of North Korea?"

Such an option has, among other weaknesses, the disadvantage of requiring a military buildup large enough that it's unlikely to go undetected – and risks triggering pre-emptive action from North Korea.

For the United States, meanwhile, the reasons against military involvement go beyond casualties. Washington's standing in the region could suffer irreparable damage.

"The risks are way too great," said Richard Bush, director of the Center for East Asia Policy Studies at the Brookings Institution, and a former member of the National Intelligence Council in the U.S.

Attack and "we lose the co-operation of China. We lose the confidence of our ally South Korea. We justify North Korea's vision of the U.S. and of itself. Many in Japan, parts of which retain the nuclear allergy, would be unhappy."

Mr. Blasko calls the whole idea "irrational."

"The risk from a pre-emptive attack so far outweighs the possible gain that I don't see how any U.S. military commander could recommend one of any sort," he said.

China, too, has repeatedly warned against military options. On Friday, Mr. Wang, the Chinese foreign minister, added: "If a war occurs, the result is a situation in which everybody loses and there can be no winner."