Activision announced today that Call of Duty: United Offensive, the expansion pack to critically acclaimed shooter Call of Duty, has gone gold and will ship to retailers September 14. The expansion features 13 new single player missions, new weapons, player abilities, and an expanded multiplayer with 11 new maps and three new modes of play. Developed by Gray Matter Interactive Studios, Call of Duty: United Offensive is rated "T" for Teen by the ESRB and will carry a suggested retail price of $29.99.