Thinks missiles, Aegis and much more.
Kyle Mizokami 
Once Japanese ISR assets detect North Korean mobile launchers in the wild, they will have to be quickly destroyed. The urgency of the antimissile campaign means that North Korean air defenses may not be adequately suppressed, making missions over the country risky.MQ-9 Reaper medium-altitude long-endurance drones could fly such missions instead, taking off from Japan loaded with fuel and munitions and flying long patrols over North Korea.
A country oriented towards pacifism and having disavowed war as an instrument of national policy, Japan is about as dissimilar from North Korea as one can get. Unfortunately for Tokyo, the two are separated by as little as 336 miles of water, and Pyongyang frequently threatens to attack its former colonial master. Now, as North Korea ruthlessly forges ahead with nuclear weapons and ballistic-missile technology, the threat to Japan has crystallized: the country once again faces the prospect of nuclear attack.
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South Korean intelligence believes the North  has mastered the technology to place a nuclear weapon on the Nodong medium-range ballistic missile, a weapon that can reach Japan. Although Japan has a two-layered ballistic-missile defense consisting of the Aegis combat system and Patriot missiles, it may find it necessary to add a third, controversial layer: eliminating nuclear-tipped missiles at the source. Here are five weapons systems, both defensive and offensive, that would help Japan deal with the North Korean missile threat.
1. Aegis Ashore:
The land-based version of the Aegis combat system that powers both U.S. and Japanese ships, Aegis Ashore would be useful in preventing North Korean missile warheads from falling on Japan. While Japan already has the Aegis ballistic missile defense system on its Kongo-class guided-missile destroyers, there are only four of them. Permanent Aegis Ashore bases would be available 24/7, freeing up the Kongo destroyers for traditional surface-warfare roles. Such a system would also be much cheaper than purchasing new destroyers.
Aegis Ashore, specifically the latest Baseline 9 version equipped with SM-3 Block IB interceptors , is effective against short- and medium-range missiles—both of which North Korea currently wields against Japan and other targets. Aegis Ashore would also bolster defenses against mass missile attacks from China, which has large inventories of medium-range ballistic missiles.
2. Global Hawk:
Japan is currently planning to purchase three RQ-4 high-altitude long-endurance drones from the United States, almost certainly with North Korea in mind. It’s not enough. In the event of war, North Korea’s rocket forces—and possibly its nuclear weapons—will scatter to avoid detection. While Pyongyang’s missile routes are somewhat predictable—the country has only five hundred miles of paved roads—the new Pukkuksong-2 medium-range ballistic missile  is based a on a tracked chassis and has some capability to travel offroad. This will drastically expand the necessary search area for any country attempting to hunt down North Korea’s mobile missiles.
An antimissile campaign against North Korea would involve multiple, simultaneous operations each requiring its own Global Hawk. Purchasing more of the high-altitude drones would allow the Japan Air Self-Defense Force to conduct multiple search, tracking and bomb-damage assessment operations at once across the length and depth of North Korea. Additional drones would also be useful as spares and to cover other regional contingencies.
3. KC-46 Pegasus tankers:
Japan has four KC-767J midair refueling tankers. Although capable aircraft, they are too few in number to support a sustained anti-ballistic-missile campaign. Japan selected the U.S. Air Force’s KC-46A Pegasus tanker in 2015. In the event of war, Japan will need to be able to conduct combat air patrols over the Sea of Japan, intercepting enemy aircraft as far away from the Home Islands as possible.
Tokyo will also need tanker support for its F-35A Joint Strike Fighters flying air-defense suppression missions and even strike missions deep inside North Korea. This sort of constant coverage will require up to a dozen or more KC-46A tankers.
4. MQ-9 Reaper drones:
Once Japanese ISR assets detect North Korean mobile launchers in the wild, they will have to be quickly destroyed. The urgency of the antimissile campaign means that North Korean air defenses may not be adequately suppressed, making missions over the country risky. MQ-9 Reaper medium-altitude long-endurance drones  could fly such missions instead, taking off from Japan loaded with fuel and munitions and flying long patrols over North Korea.
Reaper drones, brought up to the “Reaper Extended Range ” standard with wing-mounted fuel tanks, would cross the Sea of Japan and divide North Korea into a grid-like pattern consisting of “kill boxes” to which one or more drones are assigned. Equipped with  Hellfire missiles, GBU-12 five-hundred-pound bombs or GBU-38 Joint Directed Attack Munitions, the Reapers could quickly and accurately eliminate North Korean missile convoys.
5. Tomahawk cruise missiles:
In the event Japan decides to launch a preemptive attack on North Korea, it would need a weapon to “kick in the door,” destroying air-defense radars, known surface-to-air missile sites, and missiles identified as nearing launch status. Flying at low altitude, the missiles would evade North Korea’s aging air defense network, destroying their targets with a thousand-pound high-explosive warhead. Japan’s forty-two F-35A Joint Strike Fighters could then conduct follow-up strikes to continue to degrade Pyongyang’s radar network and missile air defenses.
Japan has long prided itself on maintaining the bare minimum defense capability. The country spends 1 percent of GDP on its military, just half the amount recommended to NATO member states. It has also eschewed offensive weapons, preferring to mount a purely defensive posture. The prospect of North Korean nuclear attack, however, may force the country to abandon both policies.
--- This story first appeared inThe National Interest---
Kyle Mizokami is a defense and national-security writer based in San Francisco who has appeared in the Diplomat*,* Foreign Policy*,* War is Boring and the Daily Beast*. In 2009, he cofounded the defense and security blog* Japan Security Watch*. You can follow him on Twitter:* @KyleMizokami .
This first appeared earlier in the year.