and temporarily stationed scientific and research staff are posted to some of the islands. The 2000 census counted 315 people on Johnston Atoll and 1 person on Wake Atoll. The Territory of Palmyra Atoll is an incorporated territory, separated in 1959 from the rest of the former incorporated Territory of Hawaii when Hawaii became a state. There has been no modern indigenous population, except at the 1940 census. During the late 2010s, the U.S. military began reinvesting in the airfield and other assets on Wake Island. The islands are grouped together as a statistical convenience. They are not administered collectively, nor do they share a single cultural or political history beyond being uninhabited islands under the sovereignty of the United States. They are all outside of the customs territory of the United States and have no customs duties. Except for Midway Atoll, the Pacific islands are surrounded by large exclusive economic zones and are within the bounds of the Pacific Remote Islands Marine National Monument. They are collectively represented by the ISO 3166-1 alpha-2 code UM. The individual islands have ISO 3166-2 numerical codes. The Internet country code top-level domain (ccTLD) ".um" has historically been assigned to the islands; however, the .um ccTLD was retired in January 2007. Most of the islands in the U.S. Minor Outlying Islands are closed to the public. Visitors to islands such as Jarvis Island need a permit. Palmyra Atoll is open to the public, but there is no easy way to reach it. Transportation Airports Airports in the United States minor outlying islands provide critical emergency landing points across the vast Pacific Ocean for all types of aircraft, allow for important military presence in key strategic zones, and have limited scheduled commercial services. The following is a list of island airports with ICAO (IATA) codes: PLPA: Palmyra (Cooper) Airport, Cooper Island, Palmyra Atoll PMDY (MDY): Henderson Field, Sand Island, Midway Atoll PWAK (AWK): Wake Island Airfield, Wake Island Other airports include: Johnston Atoll Airport, Johnston Atoll (Formerly PJON/JON): The airport was built during WWII, and saw significant commercial traffic during the second half of the 20th century. However, it was abandoned in 2003. Kamakaiwi Field: Howland Island (from 1937 to about 1945) Kingman Reef: The lagoon was used as a halfway station between Hawaii and American Samoa by Pan American Airways for flying boats in 1937 and 1938. Seaports Three of the islands are