Given the nature of the intelligence operations assigned to the SD, there were clear delineations between what constituted a full member (Mitglieder) of the SD and those who were considered "associates" (Mitarbeiter) with a further subset for clerical support personnel (typists, file clerks, etc.) who were connoted as V-persons (Vertrauensleute).[92] All SD personnel, whether simply associates or full members were required to swear an oath of secrecy, had to meet all the requirements for SS membership, were assigned SD code numbers (Chiffre Nummer) and if they were "above the level of V-person" they had to carry "an SD identification card."[93] The vast majority of early SD members were relatively young, but the officers were typically older by comparison; nevertheless, the average age of an SD member was approximately 2 years older than the average Nazi Party member.[94] Much like the Nazi revolution in general, membership in the SS and the SD appealed more to the impressionable youth.[95] Most SD members were Protestant by faith, had served in the military, and generally had a significant amount of education, representing "an educated elite" in the general sense – with about 14 percent of them earning doctorate degrees.[96] Heydrich viewed the SD as spiritual-elite leaders within the SS and the "cream of the cream of the NSDAP."[97]