Internal Security Unit

The Internal Security Unit (ISU) was the counter-intelligence and interrogation unit of the Provisional Irish Republican Army (IRA). This unit was often referred to as the Nutting Squad, in reference to the fact that many of the informers uncovered were shot in the back of the head (the "nut").

The unit is thought to have had jurisdiction over both Northern and Southern Commands of the IRA, (encompassing the whole of Ireland), and to have been directly attached to IRA General Headquarters (GHQ).