The fourth largest city in the nation and the largest in the entire South and Southwest, Houston is a port of entry; a great industrial, commercial, and financial hub; one of the world's major oil centers; and the second busiest tonnage-handling port in the United States (after New York). Houston has numerous space and science research firms; electronics plants; giant oil refineries; high-tech and computer-technology industries; one of the world's greatest concentrations of petrochemical works; steel and paper mills; shipyards; breweries; meatpacking houses; and factories manufacturing oil-drilling equipment, clothing, glass, and seismic instruments. More recently, Houston has become a major center of finance with a large number of banks, many of them foreign. The Texas Medical Center is the world's largest hospital complex and a leading medical research facility. Houston is served by two international airports and Ellington Field, a joint use civil and military airport. Cruise ships began sailing from the port in 1997. Because of its proximity to the Gulf of Mexico, the city is subject to hurricanes.