From a total of 11 squadrons and 3,000 men Song navy rose in one century to 20 squadrons totalling 52,000 men, with its main base near Shanghai. The regular striking force could be supported at need by substantial merchantmen; thus in the campaign of 1161 some 340 ships of this kind participated in the battles on the Yangtze. The age was one of continual innovation; in 1129 trebuchets throwing gunpowder bombs were decreed standard equipment on all warships, between 1132 and 1183 a great number of treadmill-operated paddle-wheel craft, large and small, were built, including stern-wheelers and ships with as many as 11 paddle-wheels a side (the invention of the remarkable engineer Kao Hsuan), and in 1203 some of these were armored with iron plates (to the design of another outstanding shipwright Chhin Shih-Fu)...In sum, the navy of the Southern Sung held off the Jin and then the Mongols for nearly two centuries, gaining complete control of the East China Sea.