[4] 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.

[6] 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.

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.

[7] 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.

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possible, regardless of the marital status of the mother, Groscurth actively and publicly campaigned to have the order rescinded.

[11] 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.

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.

Reichenau echoed the position of the local SS Feldkommandant(de), Josef Riedl, who "regarded the extermination of Jewish women and children as absolutely necessary."

Groscurth's report did not officially object to the children's plight itself but the inefficiency of the process and the potential detrimental effect on the fighting spirit of nearby German soldiers.

Despite his public rebuke, Groscurth was promoted to colonel and appointed Chief of the General Staff for XI Army Corps, commanded by Karl Strecker, which was subsequently committed to the Battle of Stalingrad.

[19] Groscurth and Strecker were the last senior German officers trapped in the city to surrender their command and, on the morning of 2 February, drafting the final communication sent by the 6th Army and signing it "Long Live Germany!"

He was also one of the authors of a secret memorandum written in October 1939 titled, "An imminent disaster," with diplomats Hasso von Etzdorf and Erich Kordt, outlining a potential coup against Hitler.

[22] His diaries and the documents that he saved gave important insights for historians into the workings of the early resistance to Hitler by conservatives and military officers, as well as the process of the eventual submission of the Wehrmacht to Nazi policies and SS atrocities.

[23][9] His papers from handling Müller's secret activities in Rome also provided a substantial body of evidence on the correspondence between the German resistance, the British government, and the Vatican.