Four men in four years have stepped off civvy street into the elite NZ Special Air Service after completing its gruelling selection course.

They were the successful contenders from 23 civilians who put themselves forward for the army's premier combat unit, which serves in the most hostile hotspots in the world.

Traditionally, only military personnel from the NZ Defence Force have been able to join but entry opened to civilians in 2011.

However, it's not for the weak.

The selection course, which runs over two weeks, includes Exercise Von Tempsky, which has candidates marching with a 35kg pack for 20 hours at an average rate of 3.5km an hour, with no breaks for sleep.

Candidates must also lug a 20kg fuel can with them. There's always one extra can - so the hopeful trooper has to carry two at times.

If they pass selection, they then undergo nine months of intensive training.

Civilian applicants spend two days preparing for the selection course learning military skills considered necessary to compete safely against others.

The four civilians made the grade along with 25 others who came the more traditional route through the army, navy and air force, according to an Official Information Act request on SAS recruitment.

In total, 243 people tried to enter the NZSAS during the past four years. Aside from the civilian applicants, there were 220 current personnel from the army, navy and air force. Of those, 27 got through.

Most candidates came from the army. Just one candidate made it through from the air force and the navy. There were also markedly fewer candidates from those other services - six men from the air force and 14 from the navy.

Details gleaned through the OIA show women from the NZ Army have tried for a place in the unit on three occasions since 2013 but as of now our special forces remains a male-only province.

A high-profile former NZSAS member says there's no reason why civilians shouldn't have the mental toughness to make it into the unit known for its "Who Dares Wins" motto.

Former NZSAS member John McLeod - winner of Treasure Island: Extreme - said self-motivation was a key component for anyone looking to join the unit.

"When I joined it was more about brawn and toughness and a little bit of smarts."

He said the course changed while he was a member to have a greater focus on mental stamina.

"The selection course - most of it is mind over matter. It's a mental approach more than anything else. It's having the will you want to do it.

"You focus on that pin-point - I'm going to finish and nothing else matters."

McLeod said civilians seeking roles would likely have police or ex-service backgrounds, or possibly expertise in martial arts.

The focus on mental toughness meant there was no reason women should not qualify for the unit, he said.

'We're looking for warriors. Male or female doesn't matter.'

The special forces selection program pits candidates against a number of "gates", with the final one being for those aspiring to the NZSAS.

Of those who don't progress to the NZSAS, NZDF figures show 28 men found roles with the Commando unit.

The Commando unit was formed during NZSAS Afghanistan deployments to relieve pressure on the unit by filling its domestic anti-terrorism role.

 

Army advice to applicants is the determination "to always go a little further" is more important than military skills.

An Army News recruiting article stated: "The best advice is to do selection as soon as you are ready. Selection is designed to identify those people with the qualities we need - we will teach you the skills."

An SAS officer quoted in Army News said: "For me, the SAS cycle was more about a certain mind-set rather than a physical challenge. It was about training my mind to believe I could do it, that I could achieve what I wanted to."

NZSAS selection usually takes place twice a year.

Tasks include surveillance and reconnaissance, responding to terrorist situations and providing assistance to NZ govt agencies.

The unit has been deployed to a variety of locations, including Afghanistan. Individual members of the NZSAS have received a variety of honours and awards, including the Victoria Cross awarded to Corporal Willie Apiata in 2007.