Australian war hero Corporal Ben Roberts-Smith gave Mitchell Johnson a day in the life of an SAS soldier and taught him a lesson that helped transform the once fragile paceman into a world beater playing a key role in wresting back the urn from England.

Johnson and Roberts-Smith, a recipient of the Victoria Cross for Australia, met last year when the left-armer's career was at a crossroads, his confidence shattered by a combination of poor form, serious injury and heavy criticism from the media.

But the paceman emerged a new man after being told by Roberts-Smith he needed to prioritise what was important in his life and shut out the negative press he was receiving, as it had affected his on-field performance.

While Roberts-Smith does not like comparing war and sport, he reinforced to Johnson how, in the army, there was no excuse for not getting the job done.

''You find a way no matter what it takes because, in our line of work, complacency or lack of desire can lead to loss of life,'' Roberts-Smith said.

''When we put it in those terms and he and I spoke along those lines it became clear to him what lengths we will go to by way of training and development to achieve our outcome.''

Roberts-Smith even took Johnson to his training barracks where he was given a hands-on experience of life in the army.

''We got it all cleared, I took him out on the range, we had him fast-roping out of helicopters, blowing doors in and shooting and giving him a bit of a day in the life of an SAS soldier,'' Roberts-Smith said. ''It's got to be done regardless of how you feel, you've got to get back on the horse.''

Asked how accurate Johnson's aim was, Roberts-Smith said: ''He shoots as well as he bowls at the moment, so he's not too bad.''

While the marked difference in Johnson's confidence in the past 18 months has been noted by Australian team officials, Roberts-Smith sensed the Queenslander's drive even when he was down in the dumps. He even likened Johnson's qualities to those he saw in his troops.

''You can never compare war and sport, I've always said that, but what you compare is the dedication and passion with which people play the game,'' Roberts-Smith said. ''To me, that's what Anzac spirit is. I look at it with what you're prepared to do on the field is the same as when we go into battle.

''War and sport are not the same but how you conduct yourself in those arenas certainly is and that comes down to what sort of person you are. When I say Mitchell is like one of the boys at work, what I meant was he's a guy who clearly understood what he wanted to achieve. He had a bad time - a lot of people would have packed it in and given up.

''That's why I said our whole job, our selection course, everything is based on if you're willing to give up then you're not the person we're looking for.

''If you really want to achieve something, when things are hard and going wrong, when you think like you're not going to get out of a situation, that's when we need people to stand up.

''That's the calibre of the men I work with. He got that. That reaffirmed in him the way he was before he got into his low was where he wanted to be again.''

Roberts-Smith does not want to take credit for Johnson's revival, deflecting kudos to the player's wife Jessica, but said he needed someone outside the game to show him a different perspective.

''If people get complacent [in my work] they get killed - that's our reality,'' Roberts-Smith said. ''If you want to get back into cricket, it's a much easier road and you've got all the attributes to pull that off.''