Ashton Kutcher with The Guardian co-star Kevin Costner and (below) with wife Demi Moore

In his first action film, The Guardian, Ashton Kutcher undergoes dangerous sea rescues, confronts his own demons and clashes with Kevin Costner. Before the December 8 release of The Guardian, the tall, dark and handsome actor, married to actress Demi Moore, chats about the rigours of training for the most challenging role of his career.

Describe your character.

I play Jake Fischer, a very insecure guy who comes off as a cocky, unpleasant idiot, but inside he really wants help. He comes into the Coast Guard special training programme to become a top rescue swimmer and does not really want help from anyone. Eventually he needs to ask for help.

What’s his relationship like with Kevin Costner’s character?

Kevin, who plays Ben Randall, becomes a father figure for my character, but at the start they do not get on at all. Later I realise that this job is not about competition.

What was the appeal of this role?

I really wanted to do an action film. I was also looking to work with actors who I could learn from. It was great working with Kevin Costner. He has always been a hero since I saw Field Of Dreams.

How did you prepare for this role?

You cannot really fully prepare for a role like this. You have to grin and bear it. I found out I had to hold my breath for three minutes in one scene, I would have to tow somebody through the rough water and I would probably have to do it 20 times. But when it came to filming, the pain was not a bad thing. You are wet and you are very cold all the time, so you don’t need to act it.

Is it true that you could not swim before taking this role?

I could barely swim. I just don’t like the water much. I do not like taking a bath. Swimming the way I learned for this film is about being efficient with your oxygen and swimming in comparable times to Olympic swimmers.

How much training did you do?

I trained for eight months. I made sure I could do everything the Coast Guard swimmers have to do. I started swimming every morning in a lap pool. Then I started swimming in the ocean, which was a completely different thing. I was throwing up constantly. Every time I threw up I would go back in and swim more. After the initial training, I had to go through boot camp with the other actors.

What was the boot camp like?

It was really tough. I had to ask these Olympic swimmers to take a notch off their speed. A couple of times I said “Guys I’m supposed to win this race.” But they helped me a lot. I have never been yelled at so much in my life, except perhaps by my parents.

What is your approach to acting at this point?

There is a value in reaching for the next rung on the ladder. And my desire is to do my best and make sure each role is the best work I have ever done.