Which type of weapon was the Provisional Irish Republican Army using in it's attack on Heathrow Airport
1994 Heathrow mortar attacks:  Over a five-day period, Heathrow was targeted three times (9, 11, and 13 March) by the IRA, which fired 12 mortar rounds. Barrack buster: Barrack buster is the colloquial name given to several improvised mortars, developed in the 1990s by the engineering group of the Provisional Irish Republican Army (IRA).
fired 12 mortar rounds