Thousands of South Korean riot police firing tear gas stormed the Hyundai shipyard at Ulsan, 150 miles southeast of Seoul, and battled striking workers who had been occupying parts of the sprawling facility for three months. Riot police in green combat fatigues and visored helmets knocked down barricades erected by the strikers at the country’s biggest shipyard. About 1,000 police used boats to get into the shipyard from the sea. Officers said about 200 strikers were arrested, and 700 were surrounded in a company dormitory. The strikers are demanding higher pay and recognition of their union at the shipyard, which employs 22,000 workers.