Snipers' head shots had to kill terrorists simultaneously to prevent explosions
Early on a warm summer morning, a few hours before traffic began to fill the streets, a 16-man SAS patrol took up ambush positions around a Baghdad house, writes Sean Rayment.
The soldiers had been told that the house was a being used as a base by insurgents - and up to three suicide bombers were expected to leave it later that morning.
Dressed in explosive vests, they were fully equipped to hit a number of locations around the city. The bombers' targets were thought to be cafes and restaurants frequented by members of the Iraqi security forces.
The intelligence was regarded as "high grade" and came from an Iraqi agent who had been nurtured by members of the British Secret Intelligence Service, also known as MI6, for several months.
Expectation among the 16 soldiers, attached to Task Force Black (TFB), the secret American and British special forces unit based in the Iraqi capital, was high. Each member of the four four-man groups was a veteran of many missions where the intelligence promised much - only to deliver little.
The plan for Operation Marlborough was simple: allow the three suspected bombers to leave the house and get into the street, then kill them with head shots from the four sniper teams. Each team was equipped with L115A .338 sniper rifles, capable of killing at up to 1,000 yards.
The soldiers, liaising earlier with their commanders, had considered the option of entering the house and killing the terrorists - but that plan was regarded as too dangerous. The confines of the house would intensify the impact of any blast, killing everyone inside.
The SAS soldiers were told that it was vital that the three bombers would have to be killed simultaneously.
If one of them was allowed to detonate a device, scores of people could be killed or injured.
In support of the covert sniper teams was a Quick Reaction Force (QRF), which would provide a dozen extra soldiers within a few minutes in an emergency. The QRF was based in a secure location nearby and a team of ammunition technical officers were on hand to defuse the bombs.
A section of Iraqi police was also attached to the operation - although they were not briefed on the detail of the attack - to deal with any crowd trouble.
Meanwhile, 2,000 feet above the city of five million inhabitants, a CIA-controlled Predator unmanned air vehicle was providing a real-time video feed back to the TFB headquarters deep inside the secure green zone.
Shortly after 8am, Arabic translators, monitoring listening devices hidden inside the house, warned the operations centre inside the militarily controlled green zone that the three terrorist were on the move. The message "stand by, stand by" was dispatched to the four teams.
As the terrorists entered the street, a volley of shots rang out and the three insurgents slumped to the ground.
Each terrorist had been killed by a single head shot - the snipers having spent the past few days rehearsing the ambush in minute detail.
The SAS troopers had been warned that only a direct head shot would guarantee that bombs would not be detonated.
Only three of the four snipers fired, the fourth was to act as a back-up in case one of the weapons jammed or a sniper lost sight of his target.
The message that the terrorists had been killed was sent back to the SAS headquarters and the troops moved forward to check the bodies for life. As they gingerly approached it became brutally apparent that the .338 calibre round - the biggest rifle bullet used by the Army - had done its job.
Operation Marlborough was hailed as a complete success and one of the rare occasions on which the coalition has been able to deliver a decisive blow against suicide bombers.