Anactive service unit (ASU;Irish:aonad seirbhíse cogúla)[1][2] was aProvisional 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] The concept was first pioneered byTom McEllistrim and other members of theIrish Republican Army.
In 1977, the IRA moved away from the larger conventional military organisational principle owing to its perceived security vulnerability. In place of thebattalion 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 aquartermaster 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 theSouth Armagh Brigade which retained its traditional hierarchy and battalion structure and used relatively large numbers of volunteers in its actions.[8] Some operations, like theattack on Cloghogue checkpoint or theSouth Armagh sniper squads, involved as many as 20 volunteers, most of them in supporting roles.[9]
The smallerRepublican paramilitary organisation theINLA also used the term "active service unit,[10] as did theLoyalist paramilitary groups theUlster Volunteer Force[11] andUlster Defence Association.[citation needed]
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