February 1978, a British Army Gazelle helicopter was shot down near Silverbridge, killing Lieutenant Colonel Ian Corden-Lloyd. In the 1990s, the IRA came up with a new plan to restrict British Army foot patrols near Crossmaglen. They developed two sniper teams to attack British Army and RUC patrols. They usually fired from an improvised armoured car using a .50 BMG calibre M82 sniper rifle. Signs were put up around South Armagh reading "Sniper at Work". The snipers killed a total of nine members of the security forces: seven soldiers and two constables. The last to be killed before the Good Friday Agreement was a British soldier, bombardier Steven Restorick. The IRA had developed the capacity to attack helicopters in South Armagh and elsewhere since the 1980s, including the 1990 shootdown of a Gazelle flying over the border between Tyrone and Monaghan; there were no fatalities in that incident. Another incident involving British helicopters in South Armagh was the Battle of Newry Road in September 1993. Two other helicopters, a British Army Lynx and a Royal Air Force Puma were shot down by improvised mortar fire in 1994. The IRA set up checkpoints in South Armagh during this period, unchallenged by the security forces. Downing Street mortar attack On 7 February 1991, the IRA attempted to assassinate prime minister John Major and his war cabinet by launching a mortar at 10 Downing Street while they were gathered there to discuss the Gulf War. The mortar bombing caused only four injuries, two to police officers, while Major and the entire war cabinet were unharmed. First ceasefire After a prolonged period of background political manoeuvring, during which the 1992 Baltic Exchange and 1993 Bishopsgate bombings occurred in London, both loyalist and republican paramilitary groups declared ceasefires in 1994. The year leading up to the ceasefires included a mass shooting in Castlerock, County Londonderry, in which four people were killed. The IRA responded with the Shankill Road bombing in October 1993, which aimed to kill the UDA leadership, but instead killed eight Protestant civilian shoppers and a low-ranking UDA member, as well as one of the perpetrators, who was killed when the bomb detonated prematurely. The UDA responded with attacks in nationalist areas including a mass shooting in Greysteel, in which eight civilians were killed – six Catholics and two Protestants. On 16 June 1994, just before the ceasefires, the Irish National Liberation Army