Question: What kind of airbase is the airport that only China United Airlines uses commercially?
Context: China United Airlines Co., Ltd. () is a budget airline with its headquarters in Fengtai District, Beijing, China, operating scheduled flights and charter services in co-operation with local enterprises out of Beijing Nanyuan Airport, making it the only commercial airline using this airport.  The airline previously had its headquarters in another area in Fengtai District, Beijing. Air Wisconsin Airlines is a regional airline based at Appleton International Airport in the town of Greenville, Wisconsin, United States, near Appleton.  Air Wisconsin is the largest privately held regional airline in the United States.  It currently operates regional jet flights as American Eagle under contract to American Airlines via a code sharing agreement, serving cities in the U.S. and Canada with hubs at Boston Logan International Airport (BOS), Charlotte Douglas International Airport (CLT), Philadelphia International Airport (PHL) and Ronald Reagan Washington National Airport (DCA) .  Air Wisconsin previously operated United Express service on behalf of United Airlines followed by US Airways Express service on behalf of US Airways prior to becoming an American Eagle regional air carrier.  The company has announced it will once again partner with United Airlines as a United Express code sharing air carrier with primary hubs to be located at Chicago O'Hare International Airport (ORD) and Washington Dulles International Airport (IAD) beginning in September 2017 and will be "exclusively operating" as United Express by March 2018. The Daly Waters Airfield, also RAAF Base Daly Waters, is a former commercial and sporadically-used military airfield located at Daly Waters , Northern Territory, Australia.  As Australia's first international airfield, Daly Waters was used throughout the 1920s and 1930s as a stop over for commercial airlines operating on the domestic route to Western Australia and international carriers flying from Australia into south-east Asia.  During World War II, the airbase was used by the Royal Australian Air Force (RAAF) and the United States Army Air Force to undertake combat operations against the Japanese in New Guinea, the Dutch East Indies and the islands to Australia's north.  Following the war, the airbase was used commercially again up until the 1970s when the airfield was sporadically-used by the RAAF. Stapleton International Airport was the primary airport serving Denver, Colorado, United States from 1929 to 1995.  At different times it served as a hub for Continental Airlines, the original Frontier Airlines, People Express, Trans World Airlines (TWA), United Airlines and Western Airlines.  Other airlines with smaller hub operations at Stapleton included Aspen Airways, the current version of Frontier Airlines and Rocky Mountain Airways with all three of these air carriers being based in Denver at the time. Miss China United Kingdom Pageant (Chinese: 英國華裔小姐競選), which is also known as MCUK, is an annual beauty pageant organized by OrienTouch Entertainment that selects British representatives for the annual Miss China Europe Pageant that is held in The Netherlands, organized by TVB.  With auditions and pre-selections there are 12 delegates selected for the finals held at one of Londons most impressive theaters.  With the support of TVBS-Europe, the finals of the Miss China United Kingdom Pageant will be broadcast worldwide. Shijiazhuang Zhengding International Airport (IATA: SJW, ICAO: ZBSJ) is the primary airport serving Shijiazhuang, the capital of Hebei province, China.  The airport is the hub for Hebei Airlines and a focus city for both China United Airlines and Spring Airlines.  It is also the sole airport in China that Antonov An-225 can operate. A propane bomb is a type of improvised explosive device which uses commercially available bottled gas cylinders.  The devices have been used in terror attacks and school bombing plots. Beijing Nanyuan Airport (IATA: NAY, ICAO: ZBNY) is a military airbase that also serves as the secondary airport of Beijing.  Located in Fengtai District, 3 km south of the Fourth Ring Road and 13 km from Tiananmen Square, Nanyuan Airport was first opened in 1910, making it the oldest airport in China.  It is the main hub of China United Airlines. Ghadames Airport (IATA: LTD, ICAO: HLTD) is located 12.1 mi east of Ghadames, Libya.  Currently Libyan Airlines uses the airport for scheduled service to Tripoli.  The Libyan Air Force apparently also uses the site, although this is hard to confirm visually. CASL was founded in 1995 as a joint venture among Air China Group (via CNAC(G)), British Airways, Hutchison Whampoa (China), and United Airlines.  Since the 2005, it has been a joint venture among Air China Group (40%), Hutchison Whampoa China (20%), United Airlines (20%), and China Airlines (20%).  China Airlines acquired 13.33% stake from CNAC(G) in 2005 (which was acquired from British Airways in 2003) and 6.67% from Hutchison Whampoa China.  Since 2015, Hutchison Whampoa China became a wholly owned subsidiary of CK Hutchison Holdings.
Answer: military