Anactive service unit (ASU; Irish: aonad seirbhíse cogúla)[1][2] was a Provisional Irish Republican Army (IRA) cell of four to ten members, tasked with carrying out armed attacks.[3] In 2002, the IRA had about 1,000 active members of which about 300 were in active service units.[4]
In 1977, the IRA moved away from the larger conventional military organisational principle owing to its perceived security vulnerability. In place of the battalion structures, a system of two parallel types of unit within an IRA Brigade was introduced. Firstly, the old "company" structures were used to supply auxiliary members for support activities such as intelligence-gathering, acting as lookouts or moving weapons.[5]
The bulk of attacks from 1977 onwards were the responsibility of a second type of unit, the ASU. To improve security and operational capacity these ASUs were smaller, tight-knit cells, usually consisting of five to eight members, for carrying out armed attacks. The ASU's weapons were controlled by a quartermaster under the direct control of the IRA leadership.[6] By the late 1980s and early 1990s, it was estimated that the IRA had roughly 300 members in ASUs and approximately 450 serving in supporting roles.[7]
The exception to this reorganisation was the South Armagh Brigade which retained its traditional hierarchy and battalion structure and used relatively large numbers of volunteers in its actions.[8] Some operations, like the attack on Cloghogue checkpoint or the South Armagh sniper squads, involved as many as 20 volunteers, most of them in supporting roles.[9]
The smaller Republican paramilitary organisation the INLA also used the term "active service unit,[10] as did the Loyalist paramilitary groups the Ulster Volunteer Force[11] and Ulster Defence Association.[citation needed]
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