Special Detective Unit
The Special Detective Unit ( SDU ) (Irish: Aonad Speisialta Bleachtaireachta ) is the main internal security authority of the Garda Síochána , the national police force of the Republic of Ireland , under the aegis of the Crime & Security Branch (CSB). It is the most important investigative unit for counter-terrorism and counter-espionage within the state. The Special Investigation Unit replaced the Special Branch, which in turn replaced the older Criminal Investigation Department (CID) founded in 1921. It works with the Defense Forces Directorate of Military Intelligence (G2) - the Republic of Ireland's national intelligence service - on internal affairs. The unit's headquarters are on Harcourt Street in Dublin .
The Emergency Response Unit (ERU), a specialized armed tactical unit, was a division of the SDU until 2017, when the Special Tactics and Operational Command took command of the unit.