James Gandolfini was reportedly reluctant to accept the role of Colonel Winter because he didn't understand the story and had never served in the military. He committed largely on the strength of a lengthy speech Winter delivered in the original script. Ironically, the scene was cut from the final film.
Originally, Colonel Winter was supposed to smoke cigars. James Gandolfini pleaded with director Rod Lurie to drop the idea, because he felt it would remind audiences too much of Tony Soprano, his character in The Sopranos (1999).
Robert Redford had trouble with his saluting at first. It took about twenty takes for him to do it right in the early scene where his character is, ironically, teaching Aguilar how to salute.
When Irwin is forced to move a huge pile of rocks, Robert Redford was offered fake featherweight props. He chose to carry real rocks to make the scene more realistic.