China has denied that the submarine being tracked by Japanese naval forces off Okinawa is theirs. The Japanese have a P-3 maritime reconnaissance aircraft and a destroyer following the sub, which is in international waters. The Japanese P-3 carries sensors that can confirm what type of sub is down there. The fact that the sub is larger, has been moving faster, and staying underwater longer than diesel-electric subs confirms that it is a nuclear boat. The only nations with nuclear subs in this region are the U.S., Russia and China. Russia rarely operates its subs that far south, and have apparently assured that Japanese that the boat is not theirs. An American sub would not hide its identity to Japanese forces, which leaves the Chinese. There is also a Chinese submarine rescue ship and a sea going tug in the area, giving rise to the possibility that the mystery sub is in some kind of trouble. Chinese nuclear submarines have often developed mechanical and electrical problems, leaving them dead in the water. China would not want to broadcast the fact that one of its nuclear subs is in trouble, as this would spotlight the continued failures of their nuclear submarine program.