Vietnamese army's M41 Walker Bulldog tanks were used in the movie (former South Vietnamese army tanks). During the real battle, French army used only ten M24 Chaffee light tanks.
The movie shows a formula for the distribution of Holy Communion in the Roman Catholic Mass (priest says "Corpus Christi", communicant says "Amen") that was introduced in 1969. In 1954 the priest would have said "Corpus Domini nostri Jesu Christi custodiat animam tuam in vitam aeternam. Amen" and the communicant would have remained silent.
During the bombardment of the distant hillside, with planes flying back and forth and the troops as spectators, there is perfect synchronization between the visual explosions and the sound of the same explosions. For once, in the world of film, this synchronization is incorrect: there should be a delay between the two, because of the distance to the impacts and the spectators (=the viewpoint of the camera).