With his wife, he founded the best known Dutch Nazi publishing house, De Amsterdamsche Keurkamer.
On 12 October he married Margot Warnsinck;[2] they had started the publishing house, De Amsterdamsche Keurkamer,[3] only shortly before he joined the party, on 14 or 21 July,[4] with the aim of promoting a new völkisch ideology,[5] which soon became specifically National Socialist.
[6] In the years before World War II, in addition to running the company, he edited Volk en Vaderland, the national weekly of the NSB[7] (until 1941) and wrote and published prose, poetry and essays, showing enormous energy.
In September 1942 Mussert expelled him from the NSB; Kettmann was considered too radical a Nazi.
[8][9] Ideologically he evolved from an Italian-style fascism (1931–1933) to a Dutch Nazism (1933–1940), then to a German-oriented Nazism (1940–1942) and finally to the most radical SS ideology, desiring one great Germanic empire in Europe (1942–1945).