Keira Knightley brings ''depth'' to Kenneth Branagh's 'Jack Ryan'.

The British actress stars as Cathy Ryan in the actor and director's upcoming thriller film, alongside Chris Pine as the titular character, and Kenneth knew she would enjoy the overall feel of the movie as it didn't require as much ''emotional'' input as some of her previous roles.

He said: ''I think she was a bit wrung out by the emotional engagement of what she had been doing. I thought Keira would be interested in playing a contemporary character and being in a genre that can be treated quite glibly.

''There is a physical element to the role, but it relies on her smarts, and she brings depth to her character.

''Keira has warmth and a good humour - qualities people may not associate with her because of that exotic look. Her range has expanded, she's less guarded and more confident.''

One of the reasons Keira, 28, was so keen to join the project was because none of the characters were killed off, whereas her 'Anna Karenina' alter ego committed suicide by jumping in front of a train at the end of JOE WRIGHT's 2012 film.

She joked to the new issue of Marie Claire magazine: ''I fancied doing something where everyone lives at the end.''