An underground hangar is a type of hangar for military aircraft, usually dug into the side of a mountain for protection. It is bigger and more protected than a hardened aircraft shelter (HAS). An underground hangar complex may include tunnels containing the normal elements of a military air base - fuel storage, weapon storage, rooms for maintaining the aircraft systems, a communications centre, briefing rooms, kitchen, dining rooms, sleeping areas and generators for electrical power. Countries that have used underground hangars include Albania, China, Italy, North Korea, Norway, Sweden, Switzerland, Taiwan, Yugoslavia and Iran. By country Israel Eight Israeli air force F-16I Sufa fighter aircraft were damaged in the winter of early 2020 by flooding when they were improperly left inside underground hangars in a Negev desert airbase during severe flooding. The Washington Post reported in 2012 based on the results FOIA requests to the US government that the US Army Corps of Engineers brought in US construction contractors to build installations in the south of Israel including underground hangars for fighter-bombers as a part of US military aid to Israel. Italy Built in World War II on the Island of Pantelleria. Sweden In 1941 the Swedish Air Force began building its first underground hangar at Göta Wing (F 9), located near Gothenburg in south-west Sweden, it was commissioned in 1944. After World War II plans were made up for building underground hangars at every air force base that had suitable rock conditions. These ambitious building plans proved to be too expensive and were reduced to hangars at certain select air bases. A second underground hangar was built in 1947 at Södertörn Wing (F 18). After that plans were finalized for building underground hangars capable of surviving close hits by tactical nuclear weapons. This required that these new hangars be much deeper, with 25 to 30 meters of rock cover, and heavy-duty blast doors in concrete. The Saab 37 Viggen aircraft was designed with a folding tail fin to fit into low hangars. The Aeroseum, an aircraft museum open to the public in Gothenburg, is housed in the larger cold war era Underground Hangar at Säve. Switzerland Six Flugzeugkaverne (aircraft caverns), each with space for 30 or more aircraft, were constructed for the Swiss Air Force. One at Meiringen Air Base has been expanded to operate F/A-18 Hornet aircraft. Originally, the plan for the aircraft hangar (German "Kavernenflugplatz") included the