First reported in Japan's Kyodo news agency on Thursday, unnamed Japanese officials detailed the plan was struck between the US and Japanese militaries, and arranges for a forward operating base to be establish on southwest islands, where the US Marine Corps would rapidly deploy troops.
Kyodo details that "Japan's Self-Defense Forces and the U.S. military have drawn up a draft joint operation plan that would enable the setup of an attack base along the Nansei island chain in the country's southwest in the event of a Taiwan contingency, according to Japanese government sources."
Japan's armed forces would primarily be responsible for providing logistical support, especially setting up vital ammunition and supply lines. This comes as the past year has seen Tokyo go from a much more neutral stance on the Taiwan issue to firmly and vocally being in Washington's corner, which has resulted in Beijing lashing out with warnings and threats on multiple occasions.
Beijing is certain to react fiercely to the Kyodo news report, which additionally notes that "Such a deployment, however, would make the islands the target of attack by China's military, putting the lives of residents there at risk. Legal changes would be needed in Japan to realize the plan, the sources said."
The US side has yet to confirm the agreement for the emergency plans, which appears part of longtime Washington efforts which began in earnest under the Trump administration to shore up regional allies to "stand up" to China, which has included plans for US missile bases - though so far there's no regional ally willing to make itself target #1 for China's formidable counter-measures by agreeing to host coastal missiles.
According to The Hill, "Washington and Tokyo would likely reach an agreement to start creating an official version of such a plan at the 2+2 dialogue, a high-level security meeting between diplomatic and defense officials in January."
That the US and Japanese militaries were in talks to put in place plans for intervention in the event of a PLA offensive on Taiwan was first reported in Chinese state-linked media in November. For example The South China Morning Post at the time wrote, "China has been warned to stay alert to the possibility Japan will intervene militarily in the event of an attack on Taiwan."
#Japan and US have drafted a joint plan to set up an attack base along the Nansei island chain if #Taiwan comes under threat by #China, according to Japanese government sources, reports @kyodo_official. https://t.co/b35wtVL8fC— Steve Herman (@W7VOA) December 23, 2021
The report cited that "A research paper said recent gestures of support for the island indicate that Japan and the United States have been discussing the scenario and are making plans to deter Beijing from using force to take the island."
Meanwhile, Beijing and Tokyo have continued trading threats and accusations over fishing and territorial rights in disputed islands - which in the recent past has looked poised to become a militarized dispute.