'Seán Tech to the briefing room!"
By July 2002, nine months into my job in surveillance for the British army in Northern Ireland, I had come to hate those six words squawking from the speaker in my workplace.
Without exception, they meant my workload was about to get even heavier.
There was something big going down. Our intelligence outpost near Derry, known as 'The North Det', had been a hive of activity since early morning. My radio monitoring the net was going non-stop.
Two of the operators, Baz and Damien, had been asking if I had any new covert cameras that I could fit for them. Something big was brewing.
Our job as technicians was to ensure all the operator and surveillance vehicles were fully operational.
On that day we checked in our mobile phones and pagers at the front desk of the operations building, and entered the briefing room to hear what was about to happen.
It was packed, the entire Det on a leave ban and in full op mode. (Clearly the intelligence on this one was very good. It must have come from electronic intelligence).
"Okay, lads, new operation. Everything focused on this until it finishes out," our operations officer Colin announced in his Manchester accent.
By now I knew every vehicle at North Det from a surveillance perspective, their contents and their operational status. I had also committed to memory the location of every camera that our unit had control of, and the targets they covered.
The operation to hand was around a Derry city and Strabane-based Real IRA cell. Its cell was led by a Republican figure who had been on the fringes of the Provisional IRA but had moved to the dissident movement where he could be a bigger fish in a much smaller pond. He'd previously had a reputation for being nothing but a thug and, without doubting that, we now honoured him with 'Charlie One' status for the first time, as the primary target of this surveillance operation.
Central to the operation was a white Vauxhall Cavalier car, thought from electronic intelligence to be the proposed transport vehicle for a bomb that was to be planted somewhere in our area. Only the where and when were unknown.
Our first job was to get a tracking device on the vehicle, so we could follow its movements precisely. The planting was scheduled for the Sunday-night/early Monday-morning period always favoured by operators for covert work, when the streets are at their quietest. To achieve the best surveillance results, the method we used involved temporarily stealing the target car, hopefully without anyone noticing, and then leaving an identical car with the same number plates in its place while the tracking device was embedded in the original car.
At about 3am, with the streets of Derry entirely dead, in one smooth, flowing movement, one white Vauxhall Cavalier parked on a driveway in Derry was unlocked, opened and rolled silently away while another was rolled into its place.
Within an hour, the dance was repeated and we all went home to bed.
Next morning, a liaison officer was dispatched to help direct police patrols around our operations and so avoid any so-called 'blue-on-blue incidents' which had occurred in the past.
From then on, everyone was flat out with the usual tactics. The operation was following a typical pattern: surveillance was 24 hours a day, with intelligence operators working in shifts and resting up at their temporary base at Clooney near the city.
The Cavalier was moved a few times, the Real IRA cell doing their best to counteract what they knew of the State's surveillance tactics. Eventually they even moved it across the border into the Republic, believing it couldn't be tracked there. They were wrong.
Meanwhile, the players' targets remained under constant surveillance for about two weeks.
Then, suddenly, on July 31, "Standby! Standby!" echoed around the compound, which meant get your arse in gear.
There was a buzz about the place as everyone got ready. It was late afternoon and most of us were busy on routine stuff in our own workshops. We dropped everything and went with the spooks and operators to the operations room. I was there in case something went wrong with any of the surveillance kit at the last minute. The room was fully manned, with our boss Colin at the wall of monitors, headset on, controlling the surveillance cameras and barking orders to the operators already on the ground.
The rest of the intelligence operators were dispatched, though not before checking their weapons, including SIG Sauer 9mm pistols, MP5 sub-machine guns, HK53 assault rifles and pump-action shotguns - more than enough to deal with any trouble they might run into.
"Seán, get your gear and head to the Forward Mounting Base at Clooney. I want everyone on the ground. Any faults, deal with them there."
I loaded up the tech vehicle with equipment and at the armoury I got my own SIG Sauer pistol, three loaded magazines and a HK53 complete with two full magazines.
As I drove out of the compound, I inserted my covert earpiece and made my own radio checks: "Alpha, Tuner check on three", 'Tuner' being my very apt call sign. "Lima Charlie, Tuner."
The Cavalier was on the move from the Republic across the border and into Derry. We tracked it moving around the city, stopping a few times, no doubt as counter-surveillance measures. The operators, especially the ones who had served a long time at North Det, had a grudging respect for PIRA volunteers, their discipline and training. By comparison, the dissidents were a bunch of criminal thugs, and there was not much respect for them. (The new breed of Republicans, the 'Dissidents', as they liked to be known, were all about image. Image, money and power, hidden behind the guise of the Republican tradition. The grudging respect the operators had for the old guard, the Provisionals, did not apply to this group of thugs.) But they only needed to get lucky once, so there was no complacency in how we handled ourselves.
Soon the car stopped and pulled in off the road where it was joined by another vehicle. A number of men, including our Charlie One, emerged.
The vehicles were boot to boot and the men crowded around in between as if trying to block something from view. They then split into two groups, one driving north towards Ballykelly with Charlie One now on board and the other, the Cavalier, heading south-east through Co Derry towards Armagh.
Decision time: should we stick with the Cavalier or flip to the other vehicle carrying Charlie One?
All the intelligence told us the white Cavalier would be carrying the explosives, so Colin made the call to stick with it. Now heading towards the border, with the intelligence operators following discreetly, it didn't stop at its previous hide but instead kept on heading south-east, all the way into Co Louth.
This was unexpected and Colin was worried. He directed all resources, including the PSNI, to track down the second vehicle and Charlie One.
We scoured the city and the surrounding areas down as far as Strabane, checking all the usual haunts, but it was the early hours of the next morning (Thursday, August 1) before Charlie One was found back home in Strabane. While everyone breathed a sigh of relief at this, it was a short one.
Later we heard that a civilian worker and former UDR soldier, David Caldwell, picked up a lunch box as he arrived for work at Caw Camp Territorial Army centre on the Limavady Road early in the morning.
The box contained a booby-trapped improvised explosive device and exploded, mortally injuring Caldwell. He died later at Altnagelvin Hospital.
Intelligence later gathered by North Det would show that the lunch box had been transferred from the white Vauxhall into the second vehicle.
From there it was taken some time in the early hours of the morning and planted in Caw camp. North Det had been wrong-footed.
The mood of the Det that morning was one of anger, not just at the death of David Caldwell, a father of four, but at ourselves for having failed the man.
The debriefing that followed was frank and surgical.
What had gone wrong, we asked ourselves. Where could we have done better, we debated. That night was spent in the Det bar, normal practice after an operation was concluded, but instead of the usual celebrations, it was more a case of drowning sorrows and licking wounds.
As we sat and chatted in small groups, we went over things and in a few cases tempers flared up in disagreement. That was normal, too: the tension finding a release.
It's been 14 years since the murder of David Caldwell and his family are still asking for a full enquiry. As for Charlie One on that operation, he remains committed to the Republican movement. The white Vauxhall Cavalier was found burned out in a field in Co Louth, the tracking device still working even after it had been torched.
I know it was there because I checked on it on one of my trips home to Cork later that year.
Until now, no one had any knowledge of North Det's involvement in the incident. David Caldwell's daughter, Gillian McFaul, has been looking for answers ever since that day. I hope this provides some.
Extract edited by Kim Bielenberg
As a young student from Cork with Republican links, Seán Hartnett toyed with the idea of joining the IRA. But he stunned his family when he signed up for the British army, taking an oath of allegiance to Queen Elizabeth at the Palace Barracks near Belfast.
Posted to Northern Ireland in 2001, he worked in one of its most secretive covert intelligence units. Their job was "covert surveillance and apprehension of terrorist suspects". For the next three years, using a vast network of cameras and other hi-tech equipment, he was involved in some of the highest profile events of the period. His unit, the Det, enjoyed successes in stopping armed paramilitaries. Their camera network covering vast areas of Northern Ireland was so sophisticated that they could read a number plate from 1.8km. But as he reveals in his new memoir, Charlie One, some operations went tragically wrong.
Here he tells the story of what happened on the day of the murder of David Caldwell, a former part-time soldier who was killed by a lunch-box bomb.