[JohnR34231]

The way I heard it Kubrick had seen Ermey in other movies playing a DI and was reluctant to choose him for the part  because he felt he didn't act mean enough. So, since he wanted the part, Ermey unleashed an spontaneous tirade of obscene, vulgar, and abusive language that convinced Kubrick that he had the right guy. Some of his lines do come from the book, though.

[JohnR34231]

The way I heard it Kubrick had seen Ermey in other movies playing a DI and was reluctant to choose him for the part  because he felt he didn't act mean enough. So, since he wanted the part, Ermey unleashed an spontaneous tirade of obscene, vulgar, and abusive language that convinced Kubrick that he had the right guy. Some of his lines do come from the book, though.