Born in Berlin, Erwin Planck was the fourth child of theoretical physicist Max Planck and his first wife. After his Abitur in 1911, Planck went into the military and pursued a career as an officer. In the First World War, Erwin rather quickly found himself a prisoner of the French in 1914. After the war ended Erwin came back to Germany, where he was active on the General Staff. While there he would also meet Major Kurt von Schleicher for the first time, someone who became a lifelong friend of his.
Schleicher, who headed the political branch, called Planck into the Reich Defence Ministry in 1920 and sent him as a liaison man to the Reich Chancellery, where he also became a government advisor after he left the Reichswehr in 1926.
After Hitler seized power in 1933, Planck left government work and went to East Asia for a year. Shortly after he came back to Germany, Schleicher was shot by the Gestapo. Planck tried in vain to get an explanation for his friend's murder.
In 1936, Planck changed career paths and went into business, becoming a leading employee at the Otto-Wolff-Konzern, a large conglomerate, in Cologne. In 1939, he took over leadership of the Berlin branch office.
In August 1939, a group including Prussian Finance Minister Johannes Popitz, Planck, and Reichsbank president Hjalmar Schacht approached General Georg Thomas, head of the Defence Economy and Armament Office asking him to do something to thwart the outbreak of the forthcoming war. He agreed to write a memorandum to his superior, Wilhelm Keitel, head of the Oberkommando der Wehrmacht in which he stated that a war against Poland would set off a world war that Germany could not win owing to massive supply (logistics) problems. However, Keitel tried to allay Thomas's fears by telling him that the Führer was planning no such war. Such a war, of course, began the very next month.
In 1940, Planck, Popitz, Ulrich von Hassell and Ludwig Beck drafted a "Provisional Constitution" on the assumption that the West's forthcoming attack would overthrow Hitler. Even afterwards, Planck vainly stayed in the resistance against the régime and was involved in the 20 July plot. This led to his arrest on 23 July 1944, after which he was taken to the Gestapo's Reichssicherheitshauptamt (RSHA).
A memorial plaque to Erwin Planck and two others can be found at his old school, the Joachimsthalsches Gymnasium in the Berlin borough of Wilmersdorf, Bundesallee 1-12.
- Jürgen Heideking, American Intelligence And The German Resistance: A Documentary History, Westview Press, 1998, p. 361.