Köhl was born in Neu-Ulm, Bavaria, as one of eight children. At the age of 19, he joined the German Imperial Army to become an officer like his father. At the beginning of World War I he was a Lieutenant in the Württembergisches Pionier-Bataillon Nr.13 ("13th Württemberg Pioneer Battalion"). After being wounded in the legs, which disqualified him from further service in the engineers, he volunteered to join the German Army Air Service. He became a pilot and later a commander of a Bomber Squadron and received the Pour le Mérite in 1918. He crashed his aircraft behind enemy lines and was captured and held as a POW in France but managed to escape and return to Germany.
After the end of World War I, he worked for the German Police and for the Reichswehr, but in 1925, he transferred to civil aviation and became the head of the Deutsche Luft Hansa Nightflight Branch in 1926.
By 1935, Köhl had been pushed out of German aviation circles. American journalist William L. Shirer, who befriended Koehl, wrote in his diary (later published as Berlin Diary) that "he is one of the few men in Germany with enough courage not to knuckle down to Göring and the Nazis. As a result he is completely out, having even lost his job with Lufthansa. A fervent Catholic and a man of strong character, he prefers to retire to his little farm in the south of Germany rather than curry Nazi favour. He is one of a very few."[2]
A German LuftwaffeAirbus A310 MRTTmedevac aircraft and the Bundeswehr barracks of the Transporthubschrauber-Regiment 30 in Niederstetten are named after Hermann Köhl. There is also a street in Bremen, near the airport, that is named after him.
A street in Massapequa Park, a suburb on Long Island, New York, is named after Köhl. The street was once home to Fitzmaurice Flying Park.