Guam under threat: Can the US shoot down North Korean missiles?

The United States is likely to "seriously consider" shooting down any North Korean missiles tests aimed at the waters around the US territory of Guam, but experts warn the technology isn't guaranteed to work.

Pyongyang doubled down on its threats to launch missiles at Guam early on Thursday, announcing a potential plan on state media for the "simultaneous fire of four Hwasong-12 (rockets)."

Adam Mount, senior fellow at the Center for American Progress, told CNN the US military could use its THAAD defense system or Aegis destroyers to stop any North Korean projectiles. THAAD, or the Terminal High Altitude Area Defense, is one of the US's main weapons against offensive missiles.

"If they had confidence from their readings that they would not hit US territory, it's possible they'd just let them fall into the sea, but I think they'd also take a very serious look at shooting them down," he said.

If the missiles landed within 40 kilometers (25 miles) of Guam, as threatened, according to UN law, they would fall within the United States' exclusive economic zone although not their territorial waters.

After North Korea's initial threat against Guam, the territory's Homeland Security Advisor George Charfauros told CNN he was confident of their defense systems.

"They've slowly developed their capabilities but we stand in high confidence with the US (Defense Department's) ability to not only defend Guam and the surrounding areas but also the continental US... There are several layers of ballistic missile defense."

But Bruce Bennett, a senior defense analyst at the Rand Corporation, told CNN it would ultimately be US President Donald Trump's decision whether to test their missile defenses.

"This is an experimental system -- we could potentially miss or hit, we don't know for sure. And even people who make cell phones, who have substantially more testing than THAAD does, sometimes have cell phones burn up," he said.

Mount suggested an attempt to shoot down the missile might be exactly what Kim Jong Un wants, as missing even one projectile would be an embarrassment for the US military.

How would it work?

The United States and its allies have two primary missile defense options to intercept a missile between North Korea and Guam.

In South Korea, a recently deployed THAAD missile defense system would not be able to intercept a launch toward Guam but could quickly detect the launch on its radar.

Guam itself is equipped with its own THAAD missile system, which could intercept any missiles launched from Pyongyang toward the island.

"The system's designed to engage multiple targets simultaneously, so that should be quite feasible to do," Bennett said.

However, Bennett added, it depended how far away the missiles were targeted, as the total range of THAAD was 200 kilometers (124 miles). "The closer you get to that, you're stressing the performance of the system," he said.

Alternatively, United States destroyers equipped with Aegis ballistic missile defenses could take down a missile at an even longer range, before it re-enters the Earth's atmosphere.

"The US might decide to put an Aegis system much closer to Guam to have two levels of defense, but that's a presidential decision," he said.

Carl Schuster, a Hawaii Pacific University professor and former director of operations at the US Pacific Command's Joint Intelligence Center, told CNN a single ship equipped with Aegis could probably take out two missiles.

Calling America's bluff

The United States has long trumpeted its ability to defend against missiles that threatened the country's territory, which might be what Pyongyang is counting on.

In response to North Korean missile tests, the US military has tested its missile defense system in May, and multiple times in July, although they later admitted one had failed.

But Mount said Pyongyang's threats to launch multiple missiles at Guam could be a deliberate action to call the United States' bluff on missile defense.

"It was no accident that North Korea threatened to launch four missiles, it deliberately complicates the decisions of US policy makers," he said.

If any of the four long-range missiles successfully made it through US defense, Mount said, it would be a huge victory for the rogue state.

"If the United States did try to intercept the missiles they would want to intercept all of them, because failing to intercept them all would send a message about the (US's) limited capacity ... those systems aren't perfect," he said.

Bennett said North Korea would be hoping for the US to fail, but even if the missile defenses failed it wouldn't be a disaster.

"This is a system that has never been called upon to shoot down a North Korean missile before. As a result, asking to do that for the first time, if it does, great," he said.

"If it doesn't, that means you might have some sort of software or system failure and better to find that out in peacetime rather than at war."