Captains Rhodes, wears the U.S. Army Reserve 99th Regional Readiness Command patch and the U.S. Army uniform tape. Making him and all his men U.S. Army soldiers. Throughout the film you see them all wearing the "Bakers Cap" of the U.S. Marine Corps. They would all have had the Army baseball cap.
At the beginning of the movie, the calendar on the wall show the month of October, beginning on a Tuesday. At the end of the movie, her November calendar begin on a Monday. Unless they skip several years, November should begin with a Friday. However as the calendar at the end of the movie is hand-drawn, it could be a mistake of the character, not a goof.
When the hands punch through the wall in the dream sequence at the beginning of the movie, the hand immediately to the left of the calendar picture gets stuck and forces its way through later than the rest.
When Pvt Miguel opens the gate to allow the zombies onto the lift, a zombie wearing a football helmet and jersey with MAILBOX printed above the number 22 is clearly seen. Later during Rhodes escape in the buggy we see another zombie exiting from the caverns wearing a football helmet and what appears to be the exact same jersey with a 22. However, missing from this second one, is the MAILBOX type printed above the number.