Oslo Gardermoen acts as the main domestic hub and international airport for Norway. The airport is a hub for Scandinavian Airlines, an operating base for Norwegian Air Shuttle and a focus city for Wideroe. Almost 23 million passengers traveled through the airport in 2013, making Oslo Gardermoen the 17th busiest airport in Europe.
The first flight at Gardermoen happened in 1912, and Gardermoen became a station for  military flights. However, only fields and dirt surfaces were used. During the occupation of Norway by Nazi Germany, the Luftwaffe took over Gardermoen, and built the first proper airport facilities. After World War II, the airport was taken over by the Norwegian Air Force and made the main air station.
Source: Wikipedia