India and the United States are said to be in talks to help each other track submarines in the Indian Ocean. This may further strengthen defence relations between the two countries. The talks are said to have been triggered by increased Chinese undersea activities in the Indian Ocean through which two-thirds of world trade sails through. The Indian Navy is said to have sighted Chinese submarines on an average four times every three months. Some are seen near the Andamans and Nicobar islands that lie near the Malacca Straits, the entry to the South China Sea through which more than 80 percent of China's fuel supplies pass. Therefore, it is imperative from the viewpoint of the Indian and US navies to develop a common doctrine on anti-submarine warfare (ASW). Already, the two navies conduct periodic joint naval exercises in collaboration with Japan and Australia