The Mullacreevie ambush takes place on March 1, 1991, when a mobile patrol of the Ulster Defence Regiment (UDR) composed of two Land Rover Defender vehicles is attacked with an improvised horizontal mortar by a Provisional Irish Republican Army active service unit from the North Armagh Brigade while passing near Mullacreevie housing estate, on the west side of Armagh, County Armagh, Northern Ireland. One member of the UDR is killed instantly when the leading Land Rover is hit, while another dies of wounds two days later. Two other soldiers are maimed for life.

According to author Tony Geraghty, British authorities learn of the first horizontal mortar produced by the Provisional IRA, the Mark 12, in 1985. The weapon is recovered after an incident in which three IRA volunteers are killed by security forces. The launcher suffers from the limitation of a heavy recoil, which makes the handling of the device difficult. One British intelligence report says that while the launcher is quite crude, the grenade is made of “a number of components which require a high standard of machine manufacturing.” The projectile has a warhead of 40 ounces (1.1 kg) of Semtex and TNT. It is used basically as a standoff weapon, in which the grenade is lofted over the security bases’ fences or against armoured vehicles. The mortar has an effective range of 70 yards, within which it can pierce an armour plate or destroy a sangar.

Later in the conflict the IRA develops the Mark 16, a new version with improved armour-piercing capabilities, usually referred to as a “projected recoilless improvised grenade.”

On the evening of March 1, 1991, a two-vehicle mobile patrol belonging to the 2nd Battalion, Ulster Defence Regiment is approaching the western outskirts of Armagh on Killylea road. When driving along Mullacreevie housing estate, the two Land Rovers are held by temporary traffic lights at roadworks. Unknown to them, an IRA unit from the North Armagh Brigade has set a Mark 12 launcher on a hump of earth in the front garden of a house beside the lights. After the incident, IRA sources describe the device as a “directional missile.”

When the first Land Rover pulls off after the lights turn green, the mortar ‘s improvised grenade is fired by command-wire from the backyard of the house by IRA members concealed behind a digger. The projectile hits the coachwork, blowing away both sides and the roof of the military vehicle. Witnesses report that the Land Rover was “ripped apart.” The soldiers inside are immediately assisted by fellow UDR members, who help to drag the wounded out of the shattered wreckage.

Private Paul Sutcliffe, a 32-year-old Englishman who has served for four years with the Duke of Wellington’s Regiment before becoming a UDR soldier in 1989, dies on the spot. The driver, Private Roger Love, a 20-year-old from Portadown, succumbs to his injuries three days later. Two other servicemen are maimed by the explosion. One of them suffers severe chest wounds, and loses the use of one arm; the other has a leg amputated below the knee.

The ambush at Mullacreevie is the first time that a Mark 12 mortar is used successfully.

Roger Love’s family donates the deceased soldier’s kidneys after they authorize the medical staff to disconnect the life-supporting machine. A UDR party attends Paul Sutcliffe’s funeral at his hometown of Barrowford, Lancashire, the only UDR military funeral held outside Northern Ireland. His ashes are scattered in the Mourne Mountains.

Another horizontal mortar attack on a UDR mobile patrol takes place on November 6, when Private Michael Boxall is killed in Bellaghy, County Londonderry, after the Land Rover he is riding on is hit by a Mark 12 grenade. A fellow soldier loses one eye in the attack. Incidentally, constable Erik Clarke, another Englishmen who had also served in the British Army in Northern Ireland from 1973 to 1978, is killed that year by the same kind of weapon while riding on a combined Royal Ulster Constabulary (RUC) – British Army mobile patrol in an early Mark 12 attack. The incident takes place on September 17 at Swatragh, County Londonderry. Clarke had married a local woman and later joined the RUC.

The Mark 12 mortar is used by the IRA until 1993, when it is superseded by the Mark 16. The Mark 16 is fired on eleven occasions by the IRA from late 1993 to early 1994.