Hundreds of tonnes of weapons are stored in hides ranging from deep bunkers in the midlands and south-west of Ireland to concrete-lined holes under kitchens in houses across the North.
The single most threatening item in the terrorist arsenals is the 2,500 to 3,000 kg of Semtex which is believed to be held by the Provisional IRA.
Between 1984 and 1987 the IRA smuggled 6,000 kg of the explosive into the Republic in four shipments. This was hidden in the Republic; it is estimated that since then more than half of it has been used or recovered by the security forces.
Two ounces of Semtex can make a fatal under-car booby-trap bomb; a kilo can destroy an average semi-detached house; and 20 kg reduced to powder form and incorporated in a tonne of home-made fertiliser mix produces the type of devastation seen in Canary Wharf and the City of London between 1993 and 1996.
Garda sources believe the IRA's intention is to keep its Semtex and that it may resort to the use of large bombs if it considers the Northern political process has failed to meet its expectations.
Semtex, therefore, will remain the most important "strategic" weapon in its arsenal and the most dangerous weapon held by any Irish terrorist organisation.
Some Semtex has fallen into the hands of dissident republicans, both the Continuity IRA, the small group mainly based in the north-west, and the dissident IRA group which shares the political views of the 32-County Sovereignty Committee.
This second group includes some former Provisional IRA bomb-makers. It is believed to have carried out three bombings in the North and to have attempted to ship a large car bomb to England. Security forces believe it will try to carry out more bombings.
The Continuity IRA, the group associated with Republican Sinn Fein, has less sophisticated bomb-making capability but has also acquired some of the IRA's Semtex and is expected to use it in bombs.
Loyalists acquired a commercial plastic explosive, Powergel, in unknown quantities shortly before calling their ceasefire in 1994, and still retain this. It is expected that the Ulster Volunteer Force (UVF) and Ulster Defence Association (UDA) will keep their explosives while the IRA retains its Semtex.
The Loyalist Volunteer Force (LVF), the dissident loyalist group, has acquired some Powergel, probably from sympathisers in the UVF or UDA, and may try to use it if the dissident republicans continue their bomb attacks.
On Tuesday the Irish National Liberation Army (INLA) left a booby-trap bomb in the Clonard area of west Belfast in an attempt to kill security force members. The device was discovered by local children who were lucky to escape serious or fatal injury. In the past, the INLA has killed three children in such attacks.
The INLA acquired two boxes of commercial explosive from a source in New Zealand in the mid1990s and may try to use this.
There is an array of conventional firearms in the possession of the terrorist groups, ranging from home-made guns manufactured in small factories by loyalists, to Soviet-manufactured SAM-7 ground-to-air missiles smuggled from Libya by the IRA in the mid-1980s.
The IRA is only once known to have fired a SAM-7, at a British army helicopter in Co Fermanagh in 1989. The man with the expertise to operate the missile system was subsequently jailed but is now free, so the organisation may be able to fire the two or three SAM-7s which are believed to remain in its arsenal.
The IRA also has a small number of Soviet-made heavy machine-guns and a large number of 7.62 mm medium machine-guns. It has enough AK47s and other rifles to equip a conventional infantry battalion but has never deployed more than a tiny percentage of its store of rifles.
The four ships which smuggled the weapons from Libya contained thousands of boxes of ammunition which are buried somewhere in the Republic.
Some time between 1994 and 1996 the two main loyalist groups, the UDA and UVF, also smuggled several hundred AK47s, Uzi submachine-guns and handguns into Northern Ireland. The shipment was split between the two organisations, and both are believed to have at least 200 modern automatic weapons.
The UDA used one of the Uzis from this shipment in an attack on a Catholic-owned public house on the Cliftonville Road, north Belfast, in which Mr Eddie Treanor (31) was killed and several people injured at the end of December.
The UVF has not used its new weapons but has put some on display during commemoration ceremonies in Belfast.