When he rings for his interview, it's tempting to address Robert Patrick as "sir". After all, the honorific comes with most of his roles these days. That's whether it's the various colonels he's playing in between being cast as 1950s rock'n'roll patriarchs.

In the past year he has played the father of Johnny Cash in Walk the Line and the father of the King in telemovie Elvis. The connection continues - in the upcoming Lonely Street he plays Presley as a 72-year-old man.

That will be out next year, about the same time he'll be seen in family fantasy movie Bridge to Terabithia which Patrick came to New Zealand to shoot last summer with scenes filmed at Riverhead by the same company behind the Narnia movies.

Now, the actor is getting the most screen time as Colonel Tom Ryan in The Unit, the action espionage series about a squad - and their families - in the US Army's elite Delta Force. It's the most gung-ho thing on telly at present, and that's counting 24. But there's a guiding intelligence behind all its adrenalin and testosterone.

The show was created by acclaimed screenwriter-director David Mamet, former special operations sergeant and author of the book Inside Delta Force Eric L. Haney, and Shawn Ryan, originator of the similarly hard-headed cop show The Shield.

That creative muscle and particularly the Mamet connection, was the reason Patrick signed for his second screen colonel commission - the first was in sci-fi series Stargate Atlantis - and his biggest television commitment since replacing David Duchovny in the final tepid series of The X-Files.

"You know the first thing that I look at when I looked at the pilot was David Mamet's name on it ... he does have a real great appreciation for men - men's men.

"He's a tough dude, he can take care of himself and he writes that way. I think he has a real appreciation for the guys who actually go out there and do the task."

The reason Mamet and co cast Patrick is obvious. With that headstone of a face, those icy blue eyes and that southern accent, he makes a convincing all-American hardass.

"Well, I'm a hardass," he laughs. "You know, in Hollywood you kind of go wherever they take you. And if these are the kind of roles I get hired for I guess that is their perception of me. Pretty much most of all the projects I've done I've been a guy who would be perceived as a hardass. But I don't know if I really am in real life.

"They kind of treat me like a colonel on the show and it's real easy to fall into that mode. The hard part for me is to come home and deal with my wife and kids and I want them to treat me like the colonel. All of a sudden I tell somebody to do something and they don't do it. That's a little frustrating."

Patrick says The Unit has parallels to The Sopranos, a few episodes of which he guest-starred in. "The reason I feel it's similar is because we are talking about a very secretive group of people - the men who actually go on the missions and their wives who have to protect the secrecy of what their husbands do.

"You know we don't really know a lot about the Mafia and we don't really know about the Delta Force and I think we are intrigued by that."

The actor who, as an evil robot from the future chased the present Governor of California through Terminator 2: Judgment Day, says he wasn't disappointed his Unit role doesn't require him to go into battle. His desk-driving colonel has enough excitement, he says. After all, Ryan has to deal with the Army's chain of command and military politics.

"I am not actually out there fighting with a weapon but I'm actually fighting politicians. You know, using my phones to do battle. Before, I usually would be running around with a gun and all that kind of stuff and now it's kind of got into this situation where all the fighting I will be doing is in the managing of my men."

And dealing with one of their women ... as the early episodes have shown, Colonel Ryan is having an affair with the much younger wife of one of his men.

"He's replaced the adrenalin that he used to get from going out on missions with the new danger of having an affair. He had to find something else that was as dangerous as going out on missions and that was it. But I'm not really sure why he's having the affair."

"The character I am playing is one of the most complex guys I've ever had to deal with. There's a lot of different things going on with him, there's a lot of different hats he has to wear, there's a lot of different people he has to appease, make happy, manage, keep control over. It's much more complex than I realised."

Though the show may effectively be dramatising the sharp and secretive end of US foreign policy, Patrick says he thinks The Unit is politically neutral.

"I think we are just really, truly, honestly from the point of view of the soldier. And the point of view of the soldier is really about mission and completion of mission and whatever political party is in office, that is your commander and chief. You may not politically agree with it but it's your mission and you must accomplish it. And I think we walk that line really well."

"Our show is a flag-waving show about the actual men and women who are living this life and you can't assume that all the men and women in the armed forces would vote one way or the other."

Patrick will also be seen as another colonel, a US Marine officer in Clint Eastwood's Flags of My Fathers, about the lives of the men in the famous photo taken when US forces captured Iwo Jima from the Japanese in the closing stages of World War II.

"It's kind of the same colonel. I mean it's sort of the same mindset, the guy's a little bit more colourful in Flags of Our Fathers I think but I'm certainly very proud to be in that movie and to work with Clint Eastwood. It's a real dream come true."

Who: Robert Patrick
Born: November 5, 1958, Marietta, Georgia, USA
Key roles: Terminator 2: Judgment Day (1992), Cop Land (1997), The Faculty (1998), The X Files (2002), Charlie's Angels: Full Throttle (2003), Stargate: Atlantis (2004), Ladder 49 (2004), Walk the Line (2005), Firewall (2006), Flags of Our Fathers (2006)
Latest: The Unit, 8.30pm, Mondays, TV3