Character mistake: In a conference with Crockett and Bowie, Travis states that Fannin in Goliad is preparing to relieve the Alamo and will be ready to "march south by the end of the week." Goliad is 90 miles south of San Antonio. To relieve the Alamo, Fannin would need to march north.
Character mistake: At the end, as Kenneth More and Dana Wynter emerge from the command centre, they are surprised to find that it is 9 AM, not 9 PM. Since all military and naval forces use a 24-hour clock, they would have known that the time was 0900, not 2100.