North Korea is expected to launch more ballistic missiles over Japan as the rogue nation seeks to add greater distance to its tests.

But don’t look for Japan or the United States to attempt to shoot down North Korean test missiles flying over open ocean, according to defense experts.

Downing an intermediate- range ballistic missile headed for the Pacific “would be an incredibly difficult, if not impossible, challenge,” said Kingston Reif, director for disarmament and threat reduction policy at the Arms Control Association.

“Our current defenses are not postured to defend the open ocean, but rather, major population centers, ports, military facilities, etc.,” Reif said in an email.

Beyond those concerns is the potential for failure, and the possibility that shooting a missile headed for international waters could be viewed as an act of war by North Korea.

Existing SM-3 Block IA and IB interceptors fired from Japanese and U.S. Navy ships do not have a demonstrated capability against intermediate-range missiles and have never been tested against intercontinental ballistic missiles, he said.

Patriot batteries deployed to Japan are not capable of engaging a long-range missile streaking over Japan, meanwhile.

To get a shot at the missile in space in the midcourse of flight, Aegis ballistic missile defense ships “would have to be on or very near the flight path, and perhaps even in the Pacific,” Reif said. “Ships positioned in the Sea of Japan to defend Japan against short- or medium-range missiles would likely be out of position to defend missiles on a trajectory for the Pacific.”

That proximity is needed because SM-3 IA or IB missiles don’t have the extra range to travel far both laterally and in altitude when intercepting a ballistic missile, he said.

The U.S. Missile Defense Agency said on its website that as of May 30, Aegis ballistic missile defense had a record of 35 successful intercepts in 42 attempts at ballistic missile targets.

Riki Ellison, chairman of the Missile Defense Advocacy Alliance, which seeks a strong missile defense, said North Korea “blatantly” launched what’s believed to be a Hwasong-12 intermediate-range ballistic missile Aug. 28, overflying Japan’s northern island of Hokkaido and “knowing that the missile could not be intercepted by either United States or Japanese missile defense systems and Japan could not and would not respond to this act of aggression.”

Operational U.S. and Japanese missile defense intercept systems deployed in and around Japan include Aegis ships with SM-2, SM-3 and SM-6 interceptors and the land-based Patriot missile defense, Ellison said in a release.

“All of these interceptors are designed and required to intercept in the terminal phase in lower space (Aegis) and in the earth’s atmosphere (Aegis/Patriot). They are not designed for midcourse space or boost phase and ascent intercepts,” Ellison said.

Longer-range North Korean ballistic missiles that can be fired at a high, lofted angle “can fly over these systems and interceptors when they are not deployed near the location of the ballistic missile’s terminal phase of flight,” Ellison said. “Further, these Japanese and U.S. missile defense systems, with limited capacity, are designated to defend a limited amount of high-value targets and the Japanese population.”

It would be “ill advised to waste them against North Korean test missiles that are landing in the ocean,” he said.

The Missile Defense Agency says on its website that the mainly ship-based SM-3 missiles can defeat short- to intermediate-range ballistic missiles in the midcourse of flight.

But Ellison disputes that.

“It can’t catch it at midcourse with current capability,” Ellison said by email. That will be possible with the new SM-3 Block IIA missile being developed jointly with Japan, but not yet fielded, he said.

After North Korea threatened to launch four Hwasong-12 missiles near Guam, Defense Secretary Jim Mattis on Aug. 14 said the United States would know “within minutes” where any launched missiles were heading.

“I think if they fire at the United States, it could escalate into war very quickly,” Mattis said. If a North Korean missile is headed at Guam, “we’ll take it out,” Mattis said. A Terminal High Altitude Area Defense battery on Guam could be used to guard against incoming missiles in the final stage of flight. The system is 15 for 15 in flight intercept tests.

Reif said in order for North Korea to have confidence that its long-range missiles will work under operational combat conditions, it needs to fly them at their maximum range, and that will mean more tests over Japan.

Ellison said he expects no shoot-down attempts.

“We can’t do it technically today with current capability deployed and if we could, we would not want to waste these valuable expensive limited interceptors that are in high demand in an overmatch situation for the real defense of Japan and U.S. interests,” Ellison said. “And most of all, why take the chance of starting a war? It would serve no purpose and (make) no sense at all to shoot down overflight missiles with our limited capability and capacity.”