He was recruited into the
Abwehr in 1935, eventually becoming an active conspirator in the extensive network of officers within military intelligence who were part of the German resistance under the direction of Admiral
Wilhelm Canaris. In 1938, Canaris assigned Groscurth, now a Major, to head the
Abwehr II, the "Minorities and Sabotage" section of the military intelligence service responsible for
unconventional warfare in foreign countries. Canaris feared the growing power of the
SS in such operations, particularly its influence over
Konrad Henlein, and so he sent Groscurth to the
Sudetenland, border region of
Czechoslovakia, in the run up to the planned
annexation of the Sudetenland to prepare a pro-German
fifth column under the control of the
Abwehr. His mission included strengthening moderate ethnic Germans in the area in the hope that a negotiated solution could be found and a war avoided. He collected intelligence on Czechoslovak defenses, planted secret arms dumps, and trained potential insurgents in sabotage. These activities angered
Reinhard Heydrich and the
SD, who were working to aggravate tensions in order to justify an invasion. As a part of the larger strategy of taking the Sudetenland, Hitler wanted the British to be as distracted as possible when Germany forced the issue. To this end, Canaris and Groscurth traveled to
Baghdad for a secret meeting with
Amin al-Husseini, the Grand Mufti of Jerusalem. Afterward Groscurth coordinated a weapons smuggling operation on behalf of Arab forces fighting the British in the
Arab revolt in Palestine. Groscurth's plan set up an underground route for German weapons to be sent to by sea to Lebanon and then loaded onto local Arab fishing boats, which ferried the weapons to Palestine. Despite some successes by
Abwehr elements, Henlein was greatly impressed with Hitler's victory in the Austrian
Anschluss and decided to side with the radicals backed by Heydrich. Once the Germans occupied the Sudetenland, Heydrich turned on Henlein by undermining his power and murdering or imprisoning many of his friends and allies. Terrified, Henlein's wife begged Groscurth to protect them from the SS, which Groscurth and the
Abwehr tried to do, with limited success. Although Henlein was not killed outright, he was removed from the proximity of power and was only allowed to live because of the personal relationship he had built with Hitler. After his assignment in the Sudetenland, Gorscurth successfully advocated on behalf of his subordinate
Theodor von Hippel's proposal to form the
Brandenburgers within
Abwehr II. Groscurth was replaced by
Erwin von Lahousen and promoted to be the chief of
Abteilung Heerwesen zbV, a newly created liaison unit between the
Abwehr and the
OKH. The new position proved to be key in his coordination of anti-Nazi activities between military intelligence, the regular army, and the German diplomatic corps.
Chief of Abteilung Heerwesen zbV Canaris used Groscurth's new unit as a way of giving intelligence directly to senior army commanders, with the intention of combating the growing influence of the SS and its expanding intelligence capabilities. Groscurth's new duties made him extremely well-informed and connected. He used his position and the contacts that came with it to further the resistance to Hitler and the SS, including becoming one of the primary co-ordinators between the various elements of the
Oster conspiracy. On the behalf of Canaris, he acted as the
handler for
Josef Müller's covert mission to the Vatican to secure the
Pope's support for the overthrow of Hitler. He went so far as to secure explosives for an assassination attempt. During the missions Groscurth took extensive notes for operational reference and to provide evidence of resistance to Hitler for posterity if they failed. Additionally, Groscurth was active in maintaining communications between the anti-Hitler elements in Germany and the
Chamberlain government in Britain. The communications attempted to create a deal with the British to ensure the Allies would not attack Germany if Hitler could be deposed. After Himmler provoked outrage in the
Wehrmacht with his directive that SS men should breed as many children of "good blood" as possible, regardless of the marital status of the mother, Groscurth actively and publicly campaigned to have the order rescinded. In December 1939, Groscurth traveled throughout the Western Front during the
Phoney War, disseminating reports and memorandums of atrocities committed during the
invasion of Poland passed to him by a fellow objector
Johannes Blaskowitz in an attempt to convince commanders there to act against Hitler. He visited
Wilhelm Ritter von Leeb, Erwin von Witzleben,
Gerd von Rundstedt, and
Fedor von Bock, but only Leeb was willing to take any official action by authoring a complaint to Hitler. That overall effort proved to be unsuccessful and, along with his open criticism of SS policies, created pressure on the Chief of the Army
Walther von Brauchitsch from Himmler and other sources, leading to Groscurth's eventual dismissal from military intelligence by January 1940. He was then reassigned to command an infantry battalion in the West, where he took part in the invasion of France. == Army staff officer ==