Kettmann was the eldest son of a businessman and worked for his father until the company was ruined by the financial crisis of 1930, after which he worked as a journalist. He joined the NSB on 2 August 1932. On 12 October he married Margot Warnsinck; they had started the publishing house, De Amsterdamsche Keurkamer, only shortly before he joined the party, on 14 or 21 July, with the aim of promoting a new völkisch ideology, which soon became specifically National Socialist. In 1939 the company published the Dutch translation of Hitler's Mein Kampf. In the years before World War II, in addition to running the company, he edited Volk en Vaderland, the national weekly of the NSB and wrote and published prose, poetry and essays, showing enormous energy. Over the years his relation with Anton Mussert deteriorated, as Kettmann accused Mussert of being unable to grasp the true, revolutionary nature of National Socialism. This led ultimately to his joining the Nederlandsche SS on 7 March 1942. In September 1942 Mussert expelled him from the NSB; Kettmann was considered too radical a National Socialist. He went to the Eastern Front as a war correspondent. After the war Kettmann fled to Belgium, where he was arrested in 1948. Back in the Netherlands, he was accused of:
aiding the enemy, National Socialism and antisemitism,
having written and published articles and poems glorifying National Socialism and antisemitism.
He was sentenced to 10 years in prison. After his release in 1955 he refrained from any political activity. He published some volumes of poetry, in which he demonstrates not having lost his National Socialist ideology. Ideologically he evolved from an Italian-style fascism to a Dutch National Socialism, then to a German-oriented National Socialism and finally to the most radical SS ideology, desiring one great Germanic empire in Europe. After the German defeat he returned to his ideas of the 1933-1940 period.
Selected works
1928 - De glanzende draad der goden. Novel.
1930 - De vlam der steden. Coauthor: Ru le Cavelier. Novel.
1931 - Maan op het dak. Novel.
1933 - De oceaanvlucht van een olie-man. Novel.
1935 - De jonge leeuw, verzen. Poetry.
1936 - 'Om wille van het leven, kunst en gemeenschap. Essay.
1938 - Het erf aan zee. Poetry.
1940 - Om de nieuwe cultuur. Essay.
1942 - Jong groen om den helm. Poetry.
1943 - Bloed in de sneeuw. Poetry.
1944 - De verdrevene. Novel.
1949 - Leven in tweespalt: nagelaten geschriften van een nationaal-socialist. Autobiography. Published Hilversum: Flanor, 1999, ed. Willem Huberts, introduction by Louis Ferron. Flanorreeks 37..
