Taiwan stations a total of about 18,000 troops on the offshore island of Matsu. Situated outside the mouth of the Min River, the Matsu Islands form the northern anchor of the offshore defense line commanding the Min River. The main island of the complex is Nankan, more commonly known as Matsu, from the name of the major port of the island. It is 114 nautical miles northwest of Keelung, the port city on the northern tip of Taiwan, and is the same distance north of the Kinmen Islands. There are two harbors in Nankan: Fuwo and Matsu. Other major islands of the group are Peikan, Kaoteng, Tungyin, Hsiyin, Tungchu, and Hsichu. Nankan is the largest, with an area of 10.4 sq. km. Kaoteng is located only 5.5 nautical miles (9,250 meters) from the Chinese mainland.Domestic airlines operate flights to all of the major cities on Taiwan proper, as well as to the islands of Kinmen and Matsu off the coast of mainland China. Projects have been made for construction of a new airport at Matsu (Nankan) and Matsu (Peikan).