As two great powers in Northeast Asia, Japan and China have been rivals for centuries.
Topping the list in Japan’s deterrent against China is the Soryu-class diesel-electric submarine; This is one of the most advanced non-nuclear attack submarines in the world. With a displacement of 4,100 tons, the submarine can reach speeds of 13 knots on the surface and 20 knots submerged.
The Soryu is equipped with six bow-mounted torpedo tubes, with a total of 20 Type 89 high-speed homing torpedoes and American-made Sub-Harpoon missiles. Japan’s submarines could also be the delivery vehicles for cruise missiles, should the concept of preemptive strikes, currently being debated in Japanese politics, become a reality.
There are currently eight Soryu-class submarines, with more under construction. In response to increased tensions with China and a growing People’s Liberation Army Navy submarine fleet, in 2010 Japan decided to increase its own submarine force from 16 to 22. Japan’s submarine fleet is especially worrisome for China, as the PLA Navy’s weakest point is anti-submarine warfare. In fact, China has not practiced ASW in wartime and has been institutionally deficient in both skills and assets.
And finally, what scares China the most is the US military. The Treaty of Cooperation and Security between Japan and the US means that Japan has the strongest military in the world backing them. Of course, US participation in any Sino-Japanese conflict would be subject to strict conditions. Only if Japan is the victim of an armed attack and requires US military assistance.
The US-Japan military alliance is one of America’s great successes in the post-World War II era. Previously, the alliance was built against the Soviet Union, in an all-out war, not for Japan in a territorial dispute with China. The U.S. involvement in a Sino-Japanese conflict would almost certainly lead to an all-out war. However, as long as Japan and China’s territorial disputes remain tense, it is possible that the US could be dragged into a local crisis and escalate into an all-out war.