Active service unit at a 1981 hunger strikes commemoration in Galbally, County Tyrone, 2009, as part of a re-enactment. The weapons are a Beretta AR70, a MAC-10 machine pistol (with sound suppressor) and an AK-47 assault rifle.Wall plaque in Great Denmark Street, Dublin where the 1919 IRA Active Service Unit of the Dublin Brigade was founded. Every Brigade had[citation needed] an Active Service Unit; these were[citation needed] also called "Flying Columns."
An active 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] The concept was first pioneered by Tom McEllistrim and other members of the Irish Republican Army.