In March 1933, Krebs, a fervent antisemite and member of the Nazi Party, ousted the previous mayor, Ludwig Landmann, who was Jewish.

At the outbreak of the First World War he enlisted in the Imperial German Army as a one-year volunteer with the 10th (Lower Saxony) Foot Artillery Regiment, headquartered in Strasbourg.

[2] Following Adolf Hitler's national seizure of power, the Nazis set about taking over the administration of the German states and cities.

Previously, Kerbs temporarily chaired the board of the HaFraBa Highway Construction Association and had initially tried several times to give Frankfurt the title of City of Roads.

In 1941, he was one of the keynote speakers on the occasion of the opening of Alfred Rosenberg's antisemitic Frankfurt Institute for the Study of the Jewish Question.

[citation needed] In denazification court proceedings, it was deemed that he exercised "his office fairly, correctly, cleanly and unaffected by National Socialist tendencies," and thus he was not sanctioned.

These were related to events during his time as mayor such as his instruction to the fire brigade on 9 November 1938 during the Kristallnacht pogrom, to extinguish the burning of the West Synagogue in Frankfurt, or his conflicts with Gauleiter Jakob Sprenger.

He also sought readmission as a lawyer from 1950 to 1953, which was refused to him by the Hessian Ministry of Justice, among other things because of an anti-democratic and National Socialist spirit public speech given in 1952.

It was not until November 1953, after he had resigned his mandate as a City Councillor and left the German Party, that he was readmitted to the bar and resumed work as a lawyer.