Ruhrbesetzung
Koch joined the NSDAP in 1922 (member #90). From 1922 he worked in various party positions in the NSDAP-Gau Ruhr. During the Occupation of the Ruhr, he was a member of Albert Leo Schlageter's group and was imprisoned several times by the French authorities. In 1927 he became "Bezirksführer" of the NSDAP in Essen and later the deputy "Gauleiter" of "Gau Ruhr". Koch belonged to the left wing of the party and was a supporter of the faction led by Gregor Strasser.