[3] In 1894, he won a small gold medal at the "Great Berlin Art Exhibition [de]", a major annual event that ran from 1893 to 1969.

[2] In 1898, he was one of the founders of the Berlin Secession and, together with Max Liebermann, Walter Leistikow, Otto Heinrich Engel [de], Oskar Frenzel, Curt Herrmann and Fritz Klimsch, was a member of the advisory board.

In 1923, he illustrated both volumes of Weltbrand – Deutschlands Tragödie 1914–1918 (Conflagration, Germany's Tragedy), a detailed examination of the war and its aftermath by the novelist Walter Bloem, an ardent nationalist.

In October 1928, with Theo Matejko, he was invited on the first transatlantic flight of the airship Graf Zeppelin, where he made an artistic record of the voyage.

[4] After Hitler seized power, Dettmann joined the Nazi Party and served on the board of the "Reichsverband bildender Künstler Deutschlands [de]" (Reich Association of Visual Artists).