The Glenanne barracks bombing is a large truck bomb attack carried out by the Provisional Irish Republican Army (IRA) against a British Army (Ulster Defence Regiment) base at Glenanne, near Mountnorris, County Armagh, on May 31, 1991. The bombing leaves three soldiers dead and 14 people wounded, four of them civilians.

The bombing takes place at a time when the Northern Ireland Office arranges multi-party talks, known as the Brooke/Mayhew talks, on the future of Northern Ireland. Sinn Féin members are not invited to attend because of their links with the IRA, which prevents them from being recognised as a “constitutional” party. The talks end in failure soon after.

Built in 1972, the barracks house two companies of the 2nd Battalion, Ulster Defence Regiment (UDR). Seen as an outpost, it sits on the dividing line between a Protestant area and a Catholic area. Although the military barracks itself had not been attacked by the IRA previously, seven UDR soldiers from the base had already been killed during the Troubles.

At 11:30 PM, a driverless truck loaded with 2,500 lb (1,100 kg) of a new type of homemade explosive is rolled down a hill at the rear of the barracks and crashes through the perimeter fence. According to a witness, a UDR lance corporal who alerts the base, the truck is a Mercedes, and a Toyota HiAce van carrying at least two men acts as a support vehicle. The men are seen outside the parked van, masked and armed, one with a handgun and the other with a submachine gun. This same witness alerts the base believing the IRA team are about to carry out a mortar attack, and debris thrown up on the roof by the lorry as it plunges down the hill is misinterpreted by some inside the base as a mortar projectile. Automatic fire is heard by other witnesses just before the main blast. A Reuters report claims that IRA members trigger the bomb by firing upon the driverless vehicle. It is later determined that the lorry had been stolen the day before in Kingscourt, County Cavan, in the Republic of Ireland.

The blast leaves a crater 200 ft. (61 m) deep and throws debris and shrapnel as far as 300 yards (270 m). The explosion can be heard over 30 miles (48 km) away, as far as Dundalk. This is the biggest bomb detonated by the IRA up to this point. Most of the UDR base is destroyed by the blast and the fire that follows. At first, a massive mortar attack is suspected. Some livestock are killed and windows broken around the nearby Mossfield housing as a result of the explosion. The cars parked outside the base are obliterated. Ceilings are brought down and the local primary school is also damaged.

The barracks is usually manned by eight soldiers, but at the time there are 40 people in the complex, attending a social event. Three UDR soldiers – Lance Corporal Robert Crozier (46), Private Sydney Hamilton (44) and Private Paul Blakely (30) – are killed and ten are wounded. Two of them are caught by the explosion when they come out to investigate after a sentry gives the alarm. A third dies inside the base. Four civilians are also wounded. The Provisional IRA claims responsibility two days later.

Author Kevin Toolis lists the destruction of Glenanne UDR barracks in County Armagh as part of the cycle of violence and tit-for-tat killings in neighbouring County Tyrone. The IRA later claims that the death of three of its men in the town of Coagh is a Special Air Service (SAS) retaliation for the Glenanne bombing.

The base is never rebuilt. It had outlived its operational usefulness and a decision had already been taken to close it down. The decision not to rebuild the compound raises some controversy among unionists. A memorial stone is erected by the main entrance road with the names of the UDR soldiers killed over the years while serving in Glenanne.