The SD had a mission to infiltrate key institutions of society and guide them along proper NS lines toward the future Reich. Sipo-SD emerged within the total SD as those men who would infiltrate and guide Sipo detectives toward the true State Security Corps. But many SD leaders developed other missions and an ethos that conflicted with the taint of a police spy-enforcer image. By the same token, even if the professional policemen shared an ideological conjunction with the NS revolution, they had problems with their marriage to SS-SD. For good reasons, all these men denied any true fusion of SD with police, while each branch of the police denied identity with the other.
Yet they were one, especially after the 1939 creation of the RSHA (Reichssicherheitshauptamt), a common headquarters to coordinate integration. They were one in a conglomerate within which each man could be transferred to different branches or temporarily assigned to common missions. This meant that no matter how distinct they might have remained either de jure or in their minds, de facto they were tied together in their inhumane roles. Yet the perverse power of Sipo and SD lay in the distinct, contradictory institutional images that separated Kripo from Gestapo from SD, and even the components of the SD from each other in the minds of their members. That facilitated denial of their marriage while they moved together toward their ultimate roles.
By 1936, Himmler had legal control of all the police. No longer preoccupied with strategies for gaining control, he prepared to create the Staatsschutzkorps, a term that came into common usage during 1936—1937 to express the matured version of his vision. We may never know who contributed most to the concept. It clearly grew from Hitlerian imagery and took its general form in the grand dreams Himmler began evolving before 1931. It got much of its specific form from refinements of Heydrich and the SD leadership, including the newly recruited professional policemen. For Himmler, it was to be a union of the police, the SS (and SD), and parts of the administration, into "a corps for the defense of the realm." In 1935, Heydrich spoke of the need to propagate an inner discipline and loyalty to bind together its diverse components. He turned to his SD as the vehicle for propagating that bond within his agencies.
SS-SD penetration of the police had originally been sporadic and largely uncoordinated. The process had gone two ways: policemen joined the SS-SD, and men from these organizations entered the police. After 1935, the process became more organized and deliberate, as some policemen were pressed to take SS membership. Although a total fusion of SS and state was Himmler's goal, it was only loosely achieved. Sipo was never a part of the SS. SD membership among Sipo may never have exceeded 18 percent. Although most men in command positions were SS-SD members, many of those commanders were late joiners from the ranks of the police. Many Kripo men distanced themselves from SS identity even if they formally joined. Even the more thoroughly "SSified" Gestapo only identified selectively with the SS. Despite the rhetoric of SS camaraderie, Gestapo and Kripo men often disdained their SD partners, and vice versa. Himmler and Heydrich knew they needed at least a generation to overcome this resistance. Initially, the SS would indoctrinate the existing policemen, but ultimately, the new recruits, Hitler Youth, drawn simultaneously into the SS and police, would bring the ideal corps to fulfillment. These men of the future would be free of old traditions and "reactionary" police professionalism.