Japan believes China is trying to win the ongoing struggle over some disputed islands, by wearing down Japanese resistance by sending more patrol boats and aircraft more frequently to the disputed Senkaku Islands. Last year Japan began sending small warships to patrol contested parts of the disputed Senkaku (Diaoyu in Chinese, Tiaoyutai in Taiwan) Islands. The islands are actually islets, which are 167 kilometers northeast of Taiwan and 426 kilometers south of Japan's Okinawa and have a total area of 6.3 square kilometers.
The islands were first discovered by Chinese fishermen in the 16th century and taken over by Japan in 1879. They are valuable now because of the 380 kilometer EEZ (exclusive economic zone) international law allows nations to claim in their coastal waters. This includes fishing and possible underwater oil and gas fields.
A conservative Japanese political group built a lighthouse there in 1986, to further claims of Japanese ownership. Currently, the Japanese have the most powerful naval forces in the region and are backed up by a mutual defense treaty with the United States. China was long dissuaded by that but no more. China is no longer backing off on its claims, and neither is Japan. So these confrontations are becoming more serious.
The new Chinese tactic of sending more and more boats and aircraft takes advantage of the fact that, while Japan has better ships and crews, China has more patrol boats and men. In combat Japan would have an edge, but in this endurance contest the advantage shifts to China. In response Japan is building more patrol boats, bringing retired ships back into service, and devising new tactics of its own that rely on technological advantages.