Gunnar Fridtjof Thurmann Sønsteby DSO (11 January 1918 – 10 May 2012) was a member of the Norwegian resistance movement during the German occupation of Norway in World War II. He is also known for being the most highly decorated citizen in Norway, including being the only person to have been awarded the War Cross with three swords, Norway's highest military decoration.
Sønsteby was decorated for his work as a Norwegian resistance fighter during World War II. Known also as Kjakan (The Chin) and No. 24, he participated in the resistance effort from 1940. At the time of the German invasion of Norway in April 1940, Sønsteby was living in Oslo and fought in Philip Hansteens Skiløperkompani.
Norway's regular armed forces surrendered on 10 June 1940, after two months of fighting, and the country was subsequently occupied by the Germans. Sønsteby then became involved in the underground resistance, both through Milorg and the illegal press. In 1942 he became "Agent 24" in the Special Operations Executive. After saboteur training in England in 1943, he became the contact for all SOE agents in eastern Norway and head of the Norwegian Independent Company 1 group in Oslo. This group performed several spectacular acts of sabotage; among them smuggling out plates for the printing of Norwegian kroner from the Norwegian Central Bank and blowing up the office for Norwegian forced labour, thereby stopping the Nazis' plan of sending young Norwegian men to the Eastern Front.
In addition to the attack on the labour office the recommendation for this award mentions the theft of 75,000 ration books, which allowed pressure to be placed on authorities, stopping a threatened cut in rations; the destruction of sulfuric acid manufacturing facilities in Lysaker; destroying or seriously damaging over 40 aircraft, and related equipment which were being repaired at a tram company depot in Korsvoll; destroying a railway locomotive which was under repair at Skabo; destroying a number of Bofors guns, a field gun and vital machine tools at the Kongsberg arms factory; and starting a large fire in an oil storage depot at Oslo harbour which destroyed large quantities of lubricating oil and other specialist oils.