Many people know what the SAS do but perhaps what is lesser known is how the secretive fighting force was created.
A new BBC drama starting on Sunday, from the creator of Peaky Blinders, Steven Knight, is bringing the incredible story of how the SAS was formed to the BBC.
Based on the best-selling book of the same name, 'SAS: Rogue Heroes' by Ben Macintyre, the six-part series is a dramatised account of how the SAS was formed under extraordinary circumstances during the Second World War.
Mr Knight carried out extensive research when creating the drama series and was most concerned that serving and former members of the regiment approved of the final production.
During a Q&A after the screening of the first episode in London, he explained why he wanted to tell the story of the formation of the SAS.
Speaking at the British Film Institute, he said: "Such an amazing, unbelievable, incredible story, we all think we know who they [the SAS] are, but when I started to research [and read] the Ben Macintyre book... what gets me is how young they were – 19, 20, 22, 23-years-old – boys, as far as I'm concerned, in this incredible pressure cooker situation.
"They changed the course of the battle."
In talking to soldiers about war during his research, Mr Knight said: "It seems to me that soldiers obey orders mostly and don't know why they're doing it, but what was different about the SAS was they said, 'ask why, question the order and have your own idea and do it yourself' – that was what was so different and so amazing."
The drama is based on the true story of the formation of the SAS, however, whereas with many productions, elements are exaggerated.
In this instance, Mr Knight had to tone parts down as he feared they would seem too unrealistic to the audience.
An example he gave was focused on a scene where David Stirling (played by Connor Swindells) throws an artificial grenade onto a snooker table in a bar to clear the room so he and his colleague could use it – in reality, the hand grenade Stirling threw was real.
Mr Knight said: "It's never been written down, it came as a consequence [of meeting] Mike Sadler who is the last surviving member of the original SAS. He's now 102, he was 99 when I met him.
"And he told me the story that he and Stirling were in a bar in Paris and somebody said, 'you can't use this table we're using it all night', and the hand grenade they threw was a real hand grenade.
"To make it seem realistic I turned it into a dummy hand grenade.
"They literally had to leave and run because they were beyond reason," he added.
The drama series evokes a range of emotions throughout the series, including laughter which Mr Knight says is so important.
He said: "In our conversations with members of the SAS, functioning now and people who were around, you know, in those times, [they] say that in moments of extreme danger and terror there was this alternate emotion which was humour and laughter so it's always there.
"I think that as a writer if you can use humour to access an audience's empathy, that's great, but in these situations, it was really that what they did."
The drama is based in Cairo, in 1941. David Stirling (Connor Swindells) is an eccentric young officer, convinced that traditional commando units do not work.
Because of this, Stirling creates a radical plan as he fights for permission to recruit the toughest, boldest and brightest soldiers for a small undercover unit that will create mayhem behind enemy lines.
While Mr Knight was researching SAS founder Stirling he spoke to a secretary who worked with him for 30 years. She shed some further light on his attitude to death.
Mr Knight said: "She was giving me all this stuff which was great, then she said 'and one more thing – when he used to go and leave the office (this was in the 70s) he used to go and buy a cigar and when he got to the main road', he used to close his eyes and cross the road, so he was in his early 60s and he'd still want the possibility of death."
The writer of the hit series Peaky Blinders drew similarities between the two shows.
He said: "It does seem that there is sort of a theme with Peaky and with this that there is a group of men who are probably not the easiest people to fit into conventional society.
"There's a great quote from Rudyard Kipling and I think this is the entirety of the quote, he says, 'it's Tommy this, an' Tommy that, an' throw him out, the brute'.
"'But it's hero of this country when the guns begin to shoot'.
"In other words, the people who are getting thrown out of pubs and out of restaurants and getting into terrible trouble in peace, when war comes along, they're needed."
Mr Knight hopes his latest work conveys just how brave and extraordinary the founding members of the SAS were.
He said: "I think that if anything can come from this it's that people appreciate what these people did but also to understand that they were exceptional people, but they were also, sort of, ordinary people thrown into an exceptional situation and then did what they did.
"They became heroes as a result of what they did."
SAS Rogue Heroes broadcasts at 21:00 UK time on Sunday 30 October on BBC One and BBC iPlayer.