Steve Carell consulted with his father, a WWII veteran, to prepare for his role.
Laurence Fishburne was the only actor Richard Linklater had in mind for the role of Mueller.
Sal was originally written as an Italian-American with a heavy Queens accent. Bryan Cranston suggested, with Linklater's blessing, to perform the character as half-Irish.
The novel which inspired the movie is a sequel to The Last Detail, also written by Darryl Ponicsan, which was similarly adapted to film in 1973. The Last Flag Flying's director, Richard Linklater, has stated that the two films, however, are not connected.
Bryan Cranston was initially reluctant to accept the role of Sal, since his busy schedule had him juggling a TV series, multiple movies, a Broadway play, and a book tour. He was persuaded to take the part after being impressed by the story and the caliber of the cast.