Shipbuilding is a flagship industry of South Korea that boomed since the 1960s. The growth of the industrial sector was the principal stimulus to economic development. In 1986, manufacturing industries accounted for approximately 30 percent of the gross domestic product (GDP) and 25 percent of the work force. Benefiting from strong domestic encouragement and foreign aid, Seoul's industrialists introduced modern technologies into outmoded or newly built facilities at a rapid pace, increased the production of commodities—especially those for sale in foreign markets—and plowed the proceeds back into further industrial expansion.