He rose through the ranks and became a full colonel in October 1939, and major general in April 1944, shortly before retiring.

As a lieutenant he took part in the first touring car rally around the world: the 1908 New York to Paris Race.

Koeppen's car, the Protos Wettfahrtwagen, was the first to arrive in Paris, beating the next competitor by four days.

[2] In 1909, his book about the race, Im Auto um die Welt ("The World by Car") was published and it made him a celebrity, or folk hero, in Germany.

His fame helped to popularise the toothbrush moustache in Germany, the same style later adopted by Adolf Hitler.