The extras in the film were real American GIs, in the process of being transferred from the war in Europe to the Pacific. Many of them were killed in the fighting on Okinawa - the same battle in which Ernie Pyle was killed by a Japanese machine gunner - never having seen the movie in which they appeared.
The creator of the G.I. Joe doll, Hasbro executive Donald Levin, got the idea for the action figures name from this movie. He was originally going to have several names like Rocky the Marine, Ace the fighter pilot, Salty the sailor. Levin was told to keep it to one and after struggling to name the doll he saw this movie and then licensed the name.
William A. Wellman, nicknamed "Wild Bill", was a fighter pilot in World War I and hated the infantry, and therefore had no interest in making a film about them. Producer Lester Cowan tried several times to convince Wellman to direct the film, including showing up uninvited at Christmas with gifts for Wellman's children. Wellman finally agreed to take the job only after meeting and spending several days with Ernie Pyle at Pyle's home in New Mexico, where he saw how much former infantrymen revered him.
During WW2, infantry soldier Frank Feldman wrote a letter to his wife, describing how his unit watched the movie one evening away from the battlefield. He wrote that the film was very accurate, and that many soldiers left the viewing "with tears in their eyes." The letter survives to this present day.
Sgt. Warnicke starts out carrying an M1A1 model Thompson submachine gun in North Africa at the beginning of the film, but ends up carrying - and firing - an earlier-model M1928A1 Thompson for most of the movie.