Poor Japan. While it worries about nuclear strikes from North Korea, it faces an equally potent threat from China: losing its southern islands stretching from Kyushu to Taiwan.

But the danger in this case from China is via osmosis rather than atomic attack.

At immediate risk are the tiny Senkaku islands (Diaoyu to the Chinese) near the southern end of the island chain. China claims these islands even though they have long been under Japanese control.

Since the Senkaku dispute heated up around 2010, China has steadily expanded its fishing fleet, coast guard, and naval activities around the islands.

Chinese ships are in more places, more often, and in greater numbers than the Japanese Coast Guard can handle. China’s air force also routinely intrudes into Japan’s airspace, while harried Japanese jets dutifully scramble to intercept.

In one brazen case of letting Japan know what’s in store, Beijing in August 2016 sent well over 200 fishing boats and 15 coast guard ships to the Senkakus – with China’s navy over the horizon. There was little the outmanned Japanese could do.

Not surprisingly, China reckons it can take the Senkakus whenever it wishes. It’s only a question of time before Chinese ‘fishermen’ land on the Senkakus, and the Chinese Coast Guard dares the Japanese to respond.

And there’s more to it than just the Senkakus. Telegraphing its punches as it usually does, Beijing has quietly stated that the entire island chain, known as the Nansei Shoto in Japan that includes Okinawa, is properly Chinese territory.

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Unfortunately, the Japanese (and Americans) tend to ignore such speculative aggression in hopes Beijing might forget about it. It never does.

But some Japanese do take the Chinese seriously. The Japan Self Defense Force (JSDF) is belatedly establishing a military presence in the Nansei Shoto.

It has built or intends to build small bases on several islands – Yonaguni, Miyako, Ishigaki, and Amami-Oshima. These are nominally for intelligence gathering, but will include anti-ship missiles, and air and missile defenses.

Japan’s air force has added a squadron of F15’s in Naha, Okinawa, and the Japanese navy is modestly stepping up its presence. But the overall effort is uncoordinated rather than melding each service’s unique capabilities into a coherent defensive scheme.

This is a losing strategy and Japan will eventually find itself swarmed and unable to respond. Many Japanese fishermen have already stopped visiting waters around the Senkakus where they fished for decades.

But Japan still has options to prevent being gradually overwhelmed.

First, implement a systematic plan for defending the Nansei Shoto – with the centerpiece being a Joint Task Force (JTF-Nansei Shoto) with the mission of defending the southern islands. This forces the three JSDF services – air, sea and land – to do what they won’t do voluntarily; that is, cooperate.

Then, carry on fortifying the Nansei Shoto, and routinely patrol and exercise in the region.

However, Japan cannot defend its southern islands alone. It needs US forces and when that is factored in, China’s calculus changes drastically and Japanese prospects improve correspondingly.

In 2014, President Obama declared the Senkakus fall under the US-Japan Security Treaty and US officials regularly confirm this. Yet, China continues increasing the size and frequency of naval and air intrusions into Japanese territory.

Hence, more concrete measures are required. Japan and the US need to develop a joint defense plan for the southern islands, and start regular and frequent naval and air patrols and exercises together in the Nansei Shoto region.

This is easy. In September, the USS Reagan carrier group conducted a joint exercise with the Japanese Navy in the East China Sea with an eye on the Korean peninsula. Simply adjust the focus and do more of this.

Meanwhile, US Air Force and Navy fighters can join ASDF fighters scrambling against intruding Chinese warplanes.

And at long last, stop walking on eggshells when it comes to the Senkakus. They either belong to Japan or they do not. And decades of timid behavior have simply put them at risk.

The US Navy and JSDF can immediately start using the two maritime firing ranges near the Senkakus that haven’t been used since Jimmy Carter was President in hopes of improving China’s behavior.

Finally, Japan ought to do something about Chinese political warfare and subversion on Okinawa. Ignoring it won’t make it go away – as the Americans should have learned in the Northern Marianas and Palau.

Announce that these are all just routine activities as called for in the Japan-US Security Treaty. There’s no need to explain. That’s how Beijing does it.

Combined Japanese and US forces operating together are a most difficult deterrent – not least politically – from China’s perspective. Of course China will complain about Japan and its ally defending Japanese territory. That’s nothing new. Nor is it reason to do nothing.

As former US Ambassador to China, James Lilley observed about the Chinese: “First they try to buy you. Then they try to scare you. Then they’re stumped.”