The 39-year-old 'Silver Linings Playbook' star has also grown a beard for the movie that also stars Eric Close in the role of a Defense Intelligence Agency agent, reported E!Online.
"He(Cooper) put on like 40 pounds. He's really been working hard. He looks great. He's really taken on this character... He really takes this story personally and wants to do an honorable job for Chris' memory and for his family," Close said.