The Special Security Office (SSO) is a function within multiple arms of the United States federal government and armed forces with the mission to provide a reliable and secure means to receive and disseminate Sensitive Compartmented Information (SCI) and Special Access Programs (SAP) to authorized recipients in the United States government and military organizations. In the military, they are administered by the Defense Intelligence Agency.
Systematic handling of compartmented information probably is most associated with the Special Liaison Units (SLU) originally for the distribution of British Ultra COMINT. Cleared personnel in these units and the equivalent US Special Security Offices (SSO), usually brought material to indoctrinated recipients, perhaps waited to answer questions, and took back the material. In some large headquarters, there was a special security reading room.