Under a clear blue sky one morning three weeks ago, Corporal Searle and a handful of his fellow Diggers watched as 350 Afghan troops turned out for their morning parade at a patrol base in Kandahar province.

What followed shook the Australian Defence Force to its core, and raised profound questions about Australia's decade-long involvement in the war in the Afghanistan.

An Afghan soldier - his motivation still unclear - used a machinegun to mow down 10 Australians and an interpreter, killing Lance-Corporal Luke Gavin, Corporal Ashley Birt, Captain Bryce Duffy and the interpreter, and seriously injuring seven other Australians.

The Herald is the first media organisation to visit the patrol base at Sorkh Bed, and the only one to talk to soldiers present when the Defence Force suffered its most deadly day of combat since the Vietnam War.

The patrol base squats on a plain between Route Bear - the main road between Oruzgan province and the southern city of Kandahar - and the jagged brown mountain known to the locals as Shin Ghar.

The base is home to about 40 Australian soldiers and was built to block the flow of insurgents from Kandahar province - a Taliban stronghold - into Oruzgan, where most of the Australian contingent is stationed. Thirty minutes down one of Afghanistan's rare tarmacked roads is the main Australian base at Tarin Kowt.

It is, according to the officer commanding at the base, Major John Leevers, ''a bowl of tranquillity in an ocean of chaos''. Although it recently came under rocket fire, the insurgency in the area is weak when compared with other districts in the Australians' area of operations. At 8.20am on October 29, that peace was shattered in the most brutal and inexplicable of ways. The Afghan soldiers had been dismissed by their commanding officer and the 12 Australians turned to walk back to their compound, a barricaded corner of the larger Afghan camp.

''That's when the rounds started cracking out,'' Corporal Searle tells the Herald. ''A couple of big bursts, straight up, 20 or 30 round bursts. I had my back turned, so the rounds were coming from behind me. I hit the ground straight away, looked to my left and saw splashes everywhere, ripping straight past me, probably missed me by a metre. So I crawled to my right about three or four metres, turned back around to the direction the rounds were coming from, identified him, cocked my weapon, shot him.''

It was later discovered that the Afghan soldier, a four-year veteran of the Afghan National Army, had 156 rounds left in his machinegun's 200-round magazine and another 80 in his pockets when Corporal Searle and a wounded Australian sergeant shot him.

''As I was crawling I knew blokes had been shot, and I could actually feel the percussion coming out the muzzle of his weapon, as this bloke was only 10 metres away,'' Corporal Searle said. ''At that stage, I thought I'd been shot too, because I knew he'd let a couple of big bursts go, and I thought there's no way I can't not have been shot. So after I shot him, I was patting myself down, because I knew everyone else had been shot, looking for where the wound would be. When there was nothing I just started treating guys.''

Captain Duffy and Corporal Birt were killed instantly, as was the interpreter, but Lance-Corporal Gavin was still alive.

Other Australian soldiers sprinted the 100 metres from their compound and joined Corporal Searle in frantically treating the wounded, rushing them on stretchers to the nearby medical hut. Corporal Searle says the combat medics ''stole the show'' in the minutes after the attack with their work on the seven wounded soldiers, who were flown first to a US military hospital in Germany, and later to Australia.

Within minutes helicopters arrived from Tarin Kowt and shuttled the wounded to the base hospital. At that point, Lance-Corporal Gavin was still alive. But two or three hours later the Australians left at Sorkh Bed received the shocking news that the father of three had died after arriving at Tarin Kowt.

Although they were angered by the deaths of Corporal Birt and Captain Duffy, Lance-Corporal Gavin was one of them, a long-time mate and colleague.

''He was a dedicated soldier and a dedicated father - just loved being an infantry soldier, loved being around infantry soldiers,'' Corporal Searle said.

''This trip to him was the trip of a lifetime, what he'd been waiting for for the whole of his career - training for all his career. Just the same as the rest of us, I guess. I didn't know his wife and kids, but I do know he loved his family, they were his No.1 priority. Being a family man myself, that's pretty hard to take, knowing a father has been taken away from his kids.''

Private Ben Braithwaite was one of the soldiers who ran to help, treating two Australians with gunshot wounds to the leg, and a third who had been shot through both hips. ''I spent three months in Melbourne with Gav on a course last year. The best way to describe Gav was that he was an awesome soldier and family man. He loved being at work with the boys, especially over here, but he'd never stop talking about his kids and Jacky, his wife. He was just a funny bastard,'' Private Braithwaite says.

The grief and shock of the soldiers at Sorkh Bed is tangible but the bigger questions raised by the murder of the three Australian soldiers are inescapable. What caused the Afghan soldier to turn his gun on the Australians? Can the Australian and Afghan soldiers ever work together effectively again? Should our troops even be in Afghanistan?

The Herald has heard various theories about what motivated the killer. An Afghan officer at Sorkh Bed is adamant he was a Taliban plant but the Australians have their doubts, and the Afghan general in Tarin Kowt, Mohammed Zafar Khan, says he simply does not know and possibly never will. A Defence Force investigation continues.

After the shootings, the Afghan troops at Sorkh Bed were disarmed for a couple of days, and the Australian and Afghan commanders admit relations were soured. They say trust has been regained - to an extent. But it is impossible not to notice that a machinegun is now pointed from the Australian guard tower into the Afghan compound. And no Australian enters the Afghan area without a bulletproof vest and helmet.

The signals from the Australian Diggers are equally contradictory. Corporal Searle is wary of the Afghans, but believes strongly that the actions of the ''0.01 per cent'' should not tar the rest of them. Private Braithwaite is less forgiving.

''You can't trust them. I suppose we should never have trusted them from the start, but it's just reinforced that you can't trust them,'' he says.

''You deal with it as best you can, and just hope you've good body armour and don't turn your back on them. One guy? Who's to say there's not 10? At the end of the day there could be more. To say it won't happen again is just naive.''

But every Australian soldier the Herald has spoken to in Afghanistan agrees on whether the killings should hurry Australia's exit. ''The guys who died believed this mission was making a difference. It is making a difference, if you don't think so you're blind,'' said Corporal Searle. ''We feel if we don't finish what we started, then those guys died for nothing.''