Active service unit
An Active Service Unit (ASU) was a small, autonomous cell within the Provisional Irish Republican Army (PIRA), typically comprising four to ten members tasked with executing armed operations such as shootings and bombings.[1] Introduced during a structural reorganization in the late 1970s, the ASU model adopted a cellular framework to compartmentalize knowledge and activities, thereby reducing vulnerabilities to British intelligence penetration and informant compromise.[1][2] These units formed the operational core of the PIRA's campaign during the Troubles, employing guerrilla tactics in both urban and rural settings across Northern Ireland and occasionally mainland Britain, targeting British Army personnel, Royal Ulster Constabulary officers, and civilians deemed supportive of the United Kingdom's presence.[2][3] While enabling sustained low-intensity conflict that inflicted significant casualties—primarily on security forces but also including non-combatants—the ASU structure's emphasis on secrecy and specialization amplified operational effectiveness yet drew international condemnation for tactics involving indiscriminate explosives and sectarian reprisals.[2] The system's resilience persisted until the PIRA's 1994 ceasefire, after which many ASUs disbanded amid the peace process.[3]