Unite Air Lines, Inc., trading as United Airlines, is a major airline of the United States. It is a subsidiary of UAL Corporation with corporate offices in Chicago at 77 West Wacker Drive, and its operations base in nearby Elk Grove Township. United's largest hub is O'Hare International Airport, where it has 650 daily departures. United also has hubs in Denver International Airport, Washington Dulles International Airport, San Francisco International Airport, and Los Angeles International Airport. Its largest maintenance hub is the Maintenance Operations Center at San Francisco International Airport. The airline also maintains focus city operations at Narita International Airport near Tokyo.