The most interesting story Lee told was
that he kept the savage drill instructor persona going throughout
the shoot, never getting close to the actors. He told Kubrick
that the only way this was going to work, the only way
they would look like they were scared, was if he was "Gunnery
Sergeant Hartman" 24 hours a day. So they would set up
a scene and Lee would be waiting off stage. They would yell
"Action" and he would come in raving and raging like
a pitbull. When they yelled "Cut," he would leave
the set immediately.
He did not eat with the other actors nor talk to them
between scenes. Whenever they saw him, he was the asshole
you see on screen and he never broke the illusion. Lee sad
they hated him and that he sees some of them around Hollywood
and they still will not speak with him. The fear you see on
screen was real.