Battleship director Peter Berg was so convinced a shark would attack pop star Rihanna during the making of the movie, he enlisted a security team to protect her while she was in the sea.

Berg, who filmed the action blockbuster in Hawaii, cast Rihanna in her movie debut as a naval officer, but was so concerned for her safety; he went to extra lengths while shooting in the water.

He tells movie website Omelete, "My biggest challenge was making sure Rihanna never got eaten by a shark. My fear was that I would be the director that allowed Rihanna to be eaten by a shark."

"So I was very careful - when she was in the water I had men around her and they were (to make a gesture) if they saw one."