Gannon was at the front of the plane, closest to the crew exit door. There was a loader there, a man in olive green overalls and a quilted jacket linked to the fuselage with thick webbing straps. The Nimrod was designed for high-altitude surveillance not for dropping two four-man SAS bricks out at six miles high, so the loader was far from happy about what he was being asked to do. He was more at home in a Hercules C-130 transporter. Like the SAS troopers, he was breathing from an oxygen mask connected to the plane’s central system. The Nimrod had been depressurised ten minutes earlier, when they had come close to the dropping-off point. Two of the four jet engines had been switched off so that it could be slowed to below a hundred knots.

‘Okay, communications check,’ said Gannon, into his radio microphone. One by one the troopers went through their call signs. Shepherd was Alpha Two.

Then Gannon told them to set the altimeters they were wearing on their right wrists. Thirty-two thousand feet above sea level. It would take them almost an hour to reach the target and during that time they would travel forty miles. A needle in a haystack didn’t come close to hitting a converted oil tanker sitting in the Atlantic Ocean, but the GPS-linked navigation system brought the odds down to an acceptable level. But there was no margin for error: they were doing the drop at night and if anyone missed the ship it was one hell of a long swim home.

The eight troopers split into twos and checked each other’s equipment – the oxygen supply, the webbing straps, the Irvine height-finder and the device that would ensure all the chutes opened at precisely twenty-six thousand feet.

Shepherd checked Gannon’s rig, then gave him the OK sign, a circle formed from the thumb and first finger of his right hand. Gannon checked Shepherd’s then clapped him on the shoulder. He put his masked face close to Shepherd’s ear. ‘You okay?’ he yelled, over the noise of the engines. ‘Stay close, yeah?’ He was shouting because if he used comms the rest of the troopers would hear what he was saying.

‘I’ll be fine,’ Shepherd shouted back. He’d done high-altitude high-opening drops before, admittedly never on to a ship in the middle of the ocean with little in the way of a moon, but the principle was the same: exit the plane; hope the parachute opens; guide the canopy down to the target; don’t break anything on landing. Simple.

The ship was a medium-sized oil tanker. There was a superstructure at the rear containing the bridge and crew accommodation, but all over the quarter-mile long deck there were hatches and pipes that could easily snap a leg or a hip. It would have been a difficult jump at the best of times. A HAHO drop would give them plenty of time to make the right approach, though, and the chutes were so big that they’d move in slowly. The alternative, HALO – high altitude, low opening – wouldn’t give them time to make a safe approach and Gannon had discounted it, even though it would have reduced the risk of them being spotted in the air.