[...] over the past decade, the Japanese government has invested tens of millions of dollars to make Yonaguni a bulwark in its efforts to counter Chinese military aggression, with troops, radar towers and ammunition storage sites. Japanese and American military assets there could prevent Chinese warships from entering the open Pacific farther east if conflict were to break out. The island has three tiny settlements, a small airport and a garrison of about 230 soldiers. [...] Yonaguni is a reminder that Japan's own security is linked to Taiwan's. A Chinese attack on Taiwan could threaten Japan's access to vital sea lanes and leave far-flung Okinawan islands vulnerable. (Chinese commentators have in recent years sought to raise doubts about Japan's sovereignty over Okinawa.)