The IRA made an attempt to take out the entire British War Cabinet in February 7th, 1991. With a salvo of improvised mortar bombs fired from a lorry, the Provisional IRA nearly took out the most important and high profile members of the British government in a single attack. This attacks' potential directly matches that of the Brighton bombing nearly 7 years earlier. It was daring and well-planned but fell upon bad luck.
Two of the three mortars fired came dangerously close to striking their target. One mortar hit a tree right in front of the building. Had this tree not been in the way, the mortar would have scored a direct hit on the government building. The second mortar struck the back garden of 10 Downing St. leaving a 2 metre crater and spraying shards of window glass onto the Cabinet members. The mortars were apparently miscalibrated by less than 10 degrees.
Training in mortar calibration and construction, and other related things needs to be elaborated upon. This took months to acheive acceptable levels of expertise for the active service unit. Therefore, the planning for the operation pre-dated both John Major's stint in office and the first Gulf War.
The Provisional IRA statement regarding the attack included the following: "Whether the Gulf War goes on for weeks or years, let the British government understand that, while nationalist people in the Six Counties are forced to live under British rule, the British cabinet will be forced to meet in bunkers."
The Provos had missed wiping out the entire British governmental elite by less then 15 metres. The headlines of the brilliant attempt dominated the news for the week. This attack helped to seal the thoughts in the minds of many British politicians that they would eventually have to deal with the Provos at the negotiating table.