The question is a worrisome one: What if the Jan. 13 false ballistic missile alert had been real?

Heightened tensions between the U.S. and North Korea — and the heated rhetoric between their leaders Donald Trump and Kim Jong Un — have made the threat of nuclear war seem more plausible to many people.

So, too, has the quickening pace of North Koreas’s nuclear development program. Since taking power in 2011, North Korea’s supreme leader has launched more missiles than his father and grandfather combined.

But what stands between a launched nuclear warhead and the islands, assuming we were the target? In short, it’s a ground-based missile defense.

The U.S. would have to shoot down a North Korean missile using, well, another missile.

“The ground-based interceptors are the principle and, at this point, only defense option to intercept an incoming missile,” said Dan Leaf, a retired lieutenant general and former deputy commander of U.S. Pacific Command.

“It’s a very difficult tactical problem, make no bones about it,” Leaf said. “A missile hitting a missile is technically difficult. But it has a good success rate.”

Ground-based Midcourse Defense, as it’s called by the U.S. Missile Defense Agency, relies on 44 interceptors located at Fort Greely, Alaska, and Vandenberg Air Force Base on the central coast of California between San Luis Obispo and Santa Barbara.

It also employs the Sea-based X-Band Radar — perhaps known best to some Hawaii residents as the floating golf ball at Pearl Harbor — that’s used to detect a missile while in flight.

Here’s a picture of how the system works from the Union of Concerned Scientists. The image is also used by the Hawaii Department of Defense in its own presentations on nuclear disaster preparedness:

Although it looks complicated, military leaders are confident that the ground-based interceptors will protect the U.S. and Hawaii from a North Korean ballistic missile.

But that might not always be the case as North Korea’s technology and capabilities advance.

There’s also concern that the ground-based system can be “overwhelmed.” At least that’s the term Adm. Harry Harris, the current commander of PACOM, used during a congressional hearing in Washington in April.

“I believe our ballistic missile architecture is sufficient to protect Hawaii today, but it can be overwhelmed,” Harris said while addressing the House Armed Services Committee.

“And if Kim Jong Un or someone else launched ballistic missiles, ICBMs, against the United States, then someone would have to make a decision on which ones to take out or not. So that’s a difficult decision.”

There’s also concern about just how accurate the U.S. military’s missile defense system is when it comes to taking out ballistic missiles.

According to the Missile Defense Agency, the Ground-based Midcourse Defense system has been successful in 10 of 18 tests since 1999, a rate of 55 percent.

Other components, including the Aegis missile defense system which can be deployed from U.S. Navy vessels or from land, have been more successful.

Harris has said the U.S. should continue to search for ways to increase Hawaii’s defense capabilities, but that more studies need to be performed.

One idea that is being pursued is the installation of a new land-based “discrimination” radar, with an estimated cost of $747 million, that would help detect incoming threats sooner. It discerns real warheads from decoys.

“I have suggested that we consider putting interceptors in Hawaii that defend Hawaii directly and that we look at the defensive Hawaii radar to improve Hawaii’s capability,” Harris said at the House committee hearing in April.

“That’s something we need to study much more deeply, but I think it certainly merits further discussion.”

One option that appears to be off the table — at least for now — is “operationalizing” the U.S. Navy’s Pacific Missile Range Facility at Barking Sands on Kauai.

The Pacific Missile Range Facility, commonly referred to as PMRF, is not in the business of shooting down incoming enemy missiles. It’s a research and development facility that conducts training and tests of new technology.

The facility is home to the Aegis Ashore ground-based missile system that’s currently being used for test purposes. As the North Korea missile threat grows, some have called for the system to be used in defense.

But adding PMRF to the missile defense arsenal hasn’t been a palatable option for members of Hawaii’s congressional delegation, who often refer to the facility as a “national treasure.”

Congresswoman Colleen Hanabusa, who sits on the House Armed Services Committee, was blunt in her assessment of prepping the Kauai facility for missile defense.

“We should not operationalize PMRF,” she said.

Hanabusa would rather focus on developing the new discriminating radar on the islands to increase the amount of time the military would have to react to a missile threat, as well as make a response more precise.

She also doesn’t believe Hawaii would be a primary U.S. target of a North Korean attack. Recents tests have shown North Korea has the capabilities to hit anywhere on the mainland.

“When we talk about North Korea — and we’ve always known this — diplomacy is the way to go,” Hanabusa said. “Our military, which is still the greatest in the world, need not react in a knee-jerk reaction.”

U.S. Rep. Tulsi Gabbard, Hanabusa’s colleague on the House Armed Services Committee, is similarly cautious about transforming the Kauai testing facility into part of the missile defense system.

During a campaign event at the Hawaii Capitol on Wednesday in which Gabbard endorsed Hanabusa for governor, Civil Beat asked Gabbard about the potential missile threat from North Korea and how best to protect the state.

Although the congresswoman did not provide specifics, she said the current ground-based missile defense system that’s in place is sufficient. But she underscored the need to respond to evolving threats.

“There are new technologies that are coming out and there are existing technologies that are being deployed in different places,” Gabbard said.

“It’s important to me and I know it’s important to us, to make sure that our taxpayer dollars are spent responsibly and in a way that will actually improve the defense of Hawaii. And that’s really the bottom line.”

Leaf, the former PACOM deputy commander who also headed the Daniel K. Inouye Asia-Pacific Center for Security Studies, has a different take.

He believes the military needs to be more creative when it comes to complicating Kim Jong Un’s strategic thinking.

The discriminating radar is a good idea, but Leaf noted that it won’t be operational until at least 2023.

In the meantime, he said the U.S. should take a serious look at using the Aegis Ashore system as a backup to the ground-based interceptors in Alaska and California.

Leaf would also like the military to consider installing a Terminal High Altitude Area Defense ballistic missile system, or THAAD, in Hawaii. A similar system is currently based in Guam.

If the U.S. can show that Hawaii is properly defended, he said, it could act as a deterrent.

But he still considers an attack, though a real threat, highly unlikely.

 “I’ll be honest and tell you I don’t lose sleep over it,” Leaf said. “I didn’t wake up Saturday morning during the false alarm thinking this could be it. I didn’t wake up that way today. But this is a realistic threat.”