The first phase, which has been unchanged since the Fifties, is a series of timed marches — an individual effort over demanding terrain in the Brecon Beacons carrying a 45lb rucksack with a rifle and water bottle.
This very tough month begins with the basic military physical tests followed by a ‘beast’ (fierce march) over Pen Y Fan, the highest peak in the Beacons.
It is a timed march officially called ‘High Walk’ but known universally as ‘Fan Dance’ — in reference to the name of the peak.

A file picture of SAS recruits taking part in the incredibly arduous 'selection' training course over the Brecon Beacons in Wales
Next comes a three-week map-reading tour of the hills and then Test Week, during which the most gruelling marches are undertaken. These become increasingly challenging as the loads get steadily heavier until the final march: ‘Endurance’.
This is 40 miles long and has to be completed without stopping, within a certain time and while carrying a 60lb rucksack, a rifle and a full water bottle.
At the end of Endurance, the course numbers will be about halved and the survivors will have won a place on ‘continuation training’, including the jungle phase in Brunei.
The officers on the course face the additional hurdle of Officers’ Week which further thins out the survivors.
By the end, the whole process will have discovered those who have what it takes to wear the winged dagger of the SAS.
On my test, in 1988, a summer selection beginning in August, we started with 24 officers and 204 men. By the end of Test Week, we were down to 12 officers and 50 soldiers. By the end, just three officers and 21 men of the original 228 received the coveted sandy coloured beret and winged dagger badge.
That was a remarkably high score rate — particularly for officers.
On the previous Test, only one passed. On the next two, there were no officers selected.
Over my years in the SAS, I watched many Selections and as operations officer in the mid-Nineties. I worked with an SAS legend called Liam Collins or ‘Ginge’.
Ginge would set off at a hell of a pace followed by the men.
As we walked, I would see guys keeping pace with Ginge — sadly no longer with us, he died as a result of complications from an old injury — but as we turned at the half-way point, his followers would be fewer.
It was my task at the back of the group to keep the pace at which a candidate would pass and also to keep an eye out for the tell-tale signs of heat exhaustion. As candidates fell behind me, I would strike up a conversation with them to gauge how they were.
I’d always ask if they were drinking water and wave my half-full mug at them. It was always a close call whether to stop someone if they were jabbering incoherently.

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You realised you could be ruining his chance of selection. But you might also have to save his life. If you did have a heat casualty, the drill was straightforward. Get them on the deck, get their trousers and boots off, as well as their gear, and then give them a saline drip in their behind.
It was crude and undignified, but the fastest way to get fluid into a dangerously ill man.
At the end of each march, the shattered survivors would change out of their sweat-soaked gear with excited banter.
Those who had failed to make the cut would usually sit in dejected silence on their gear. And, once more, the staff would watch for those about to keel over. However, this was not common. I have fond memories of these tests but there was also tragedy.
There were accidents — infrequent, but they did occasionally happen.
On one Selection, a member of the support staff was shot dead in a jungle mix-up of live and blank ammunition.
That was more than 20 years ago but the lessons learned from that incident are still rigidly enforced.
In 1981, two candidates died during the selection test. According to Regiment legend, the commanding officer summoned Warrant Officer ‘Lofty’ Wiseman who ran the course. ‘What are we supposed to say about this Lofty? There are questions in the Commons.’
Lofty responded: ‘The way I see it, sir, is that it’s Nature’s way of telling them they’ve failed.’
Army humour is dark. SAS humour is pitch black.
Naturally this latest incident is attracting particular scrutiny as it involves members of the Territorial Army (TA) — the reservist force that now constitutes about a quarter of the British Army.
The fact is that since the Government has elected to base its defence policy on increased reliance on reserves, then the TA must be selected to the same standard as the regulars.
They always were in any case.
The deaths at the weekend were a terrible tragedy and I feel for the families of those lads, but they weren’t the first deaths and nor will they be the last.
The fact is that deaths are uncommon and we have to keep them in perspective.
There can be no compromise.
If our special forces are to remain world leaders then we have to maintain the highest standards.
I have no doubt that the ‘elf and safety’ experts will be clamouring to get involved.
But for those who are worried that the courses are too tough, too gruelling, too dangerous, I have some advice. ‘Don’t volunteer for SAS Selection.’
Simple.
Conversely, I welcome anyone who wants to serve in the most respected military organisation on earth.
It needs more volunteers — and as the world becomes more unstable, we need the SAS more and more.