WASHINGTON (AFP) - North Korea's latest missile launch over Japan set sirens blaring and triggered alerts telling people to seek shelter - yet neither Tokyo nor Washington tried to shoot the rocket down.
The test follows one in August that saw another rocket soar over Hokkaido. In that case too, much-vaunted Japanese and US missile-intercept capabilities were not used.
Now some in the United States are wondering why all this sophisticated weaponry isn't being used, especially as North Korean leader Kim Jong Un accelerates towards his goal of building a nuclear missile capable of striking the United States.
"The next time the North Koreans launch a rocket, especially one that will traverse over our ally Japan, I would hope that we shoot it down as a message to the North Koreans and to other people, like in Japan, who are counting on us," Republican Congressman Dana Rohrabacher told lawmakers this week.
"Unless we demonstrate we're willing to use force, there's no reason for them to believe we will."
The US Pacific Command confirmed Friday's rocket was an intermediate-range ballistic missile (IRBM), and Seoul's defence ministry said it probably travelled around 3,700km, hurtling to a maximum altitude of 770km.
The missile, which fell in the Pacific Ocean, represented North Korea's furthest-ever flight.
Evans Revere and Jonathan Pollack of the Brookings Institution wrote in a paper that Washington should declare that any future North Korean missiles towards or over US or allied territory would be deemed a direct threat that would "be addressed with the full range of US and allied defensive capabilities".
Why no shoot down
The United States and Japan together claim they can shoot incoming missiles, but officials say Friday's siren-sounding launch didn't meet that threshold.
If the US and its allies "would have determined that it was a direct threat, we would have shot it down," said Pentagon spokesman Colonel Rob Manning, noting the military's "deep arsenal of capabilities".
For Japan, these include advanced Patriot batteries, which can stop lower altitude missiles, and SM-3 missiles it is developing with the US that can take out high-flying short- to intermediate-range ballistic missiles.
The technology is imperfect but the Pentagon has demonstrated it can hit ICBM and intermediate-range missile targets.
Bruce Klingner, a senior research fellow at the Heritage Foundation, noted that when North Korea flies a missile over Japan, it travels higher than the capabilities of any ballistic missile-defence system stationed nearby, including the SM-3.
Also, Japan is a pacifist country constitutionally limited to taking military action only in self defence.
Hideshi Takesada, a North Korea and defence expert who is a professor at Takushoku University in Tokyo, told AFP that Japan plans to intercept a missile only when it enters its territorial air or objects fall onto Japanese territory.
Recent missiles have flown far above Japan and nothing fell to the ground.
"Therefore, the government did not issue a destruction order," Takesada said.
While Japan has decent anti-missile technology, it's difficult to cover the entire Japanese archipelago, experts noted.
"Also, it's technically hard to judge if a missile flying in an early stage can actually be a direct threat to the Japanese territory," Akira Kato, an international politics professor at J.F. Oberlin University in Tokyo, told AFP.
Japan and the United States do not want to risk trying an intercept unless it is posing a certain threat. A failed attempt could cause wide alarm and tip off Kim about any limitations.
"A potential failure in intercepting a missile could only result in giving an unnecessary impression that Japan's capability of missile defence is insufficient," Kato said.
Japan also has a network of Aegis missile-defence destroyers, and President Donald Trump wants Tokyo and South Korea to increase buys of such US gear. In Japan's case, that could include the purchase of a land-based version of Aegis.
According to the New York Times, the US saw Friday's missile being fueled up a day earlier.
Current US missile-defence technologies focus on stopping a North Korean missile when it is in mid-flight or during the "terminal" stage of its ballistic arc as it plummets towards its target.
But the Pentagon also wants to develop technologies to take out missiles the moment they leave the launch pad, when they are in their so-called "boost phase". The missiles at that point are laden with explosive fuel and traveling more slowly, so are more vulnerable and could be taken out with another missile launched from nearby.
The US military is also exploring launching cyber attacks and even the possibility of mounting lasers on drones, making them capable of shooting down ballistic missiles shortly after launch.