Other mistake: Capt Cahill was declared dead after the helicopter he was in crashed and then taken captive. I spent almost 24 years in the military and know that if a body is not found, even though presumed dead, the official status is Missing in Action (MIA). The notification to Capt Cahill's family should have been MIA not dead.
Continuity mistake: When the butterfly clips are put onto Tommy's head after the fight, the amount of blood on them through the following scenes that night and the next day varies from bloody, to clean, to bloody again, over and over again.
Continuity mistake: After Grace kisses Tommy she is in bed wearing the necklace with the ring, then she holds the letter and lies down again but the necklace is gone.