Background
He was born in Kristiansand as a son of port magistrate John
He was born in Kristiansand as a son of port magistrate John
He finished his secondary education in 1920 and took the candidate.philol.
East. Tønnessen and Ida, née Stray. degree at the Royal Frederick University in 1928, majoring in history and minoring in French and Latin. He also took pedagogy in 1926 and was a substitute at Trondhjem Cathedral School from 1927 to 1928. He was a teacher at Gjøvik Upper Secondary School from 1928 to 1935 and Grefsen Upper Secondary School from 1935 to 1959.
In Gjøvik he was elected to the city council in the Norwegian local elections, 1934.
He represented the Fascist party Nasjonal Samling, which with 10.9% of the vote had its third most successful city election in Gjøvik. Moving to Oslo, he did not finish the term.
During the occupation of Norway by Nazi Germany, when Nasjonal Samling was actually propelled to power as a collaborationist party, Tønnessen was arrested by the authorities in August 1943 for resistance work. He was imprisoned in Bredtveit concentration camp until November, then in Møllergata 19, then from April to October 1944 at Akershus Fortress, and ultimately in Grini concentration camp until the war"s education
Tønnessen later took the dr.philos. degree in history, and issued the books Ole Nielsen (Aalgaard) og hans slekt (1953), Kaperfart og skipsfart 1807–1814 (1955), Porsgrunns historie (two volumes in 1956 and 1957).
He contributed to Den norske sjøfarts historie (1951), Den moderne hvalfangst historie (1968–1970) and the third volume of Kristiansands historie (1974). His specialties were shipping, privateering, whaling and town history.
He became a member of the school board and deputy member of the municipal council of Aker.