Principal DoD official in a U.S. embassy, as designated by the Secretary of Defense. The SDO or DATT is the Chief of Mission's principal military advisor on defense and national security issues, the senior diplomatically accredited DoD military officer assigned to a diplomatic mission, and the single point of contact for all DoD matters involving the embassy or DoD elements assigned to or working from the embassy. The SDO or DATT is considered the dual-hatted chief of both the security cooperation organization (SCO) and defense attaché office (DAO) in the embassy. This position was established by DODD 5105.75, Department of Defense Operations at U.S. Embassies, December 21, 2007. The same document gives coordinating authority (see glossary definition) to the SDO or DATT for the purpose of ensuring that all DoD elements in a country are working in consonance with each other and under the guidance of the Chief of Mission. The SDO or DATT program replaces the now defunct U.S. Defense Representative (USDR) model.