Director Don Siegel did not want to shoot the scene where Bob Newhart's character has a fake telephone conversation with "headquarters" to fool the Germans listening through a microphone planted in the US bunker, believing that it had no place in the story. He was overruled by the studio, however. Newhart at the time was a hugely popular stand-up comic, and a major part of his act was having one-sided phone conversations. The studio ordered that the scene be shot in order to capitalize on Newhart's popularity. Newhart wrote his own lines for this scene.
Pfc. James E. Driscoll: [fake telephone conversation with "headquarters" to fool the Germans listening in] Uh - Hi. Temple Red to - uh - Abel 6. This... This is Lt. Driscoll - the - uh - the entertainment officer.
Pfc. James E. Driscoll: About the morale, sir, it's been rather low. Uh - the main complaint seems to be about the evening movie.
Pfc. James E. Driscoll: Y-Yes, sir. I've had to show 'Road to Morocco' five evenings now in a row, sir.
Pfc. James E. Driscoll: Well, the men are beginning to be a little surly, sir.
Pfc. James E. Driscoll: Yes, sir. They know all the lines.
And the Family Guy spoof - "On The Road To Rhode Island"
Back to "Hell is for Heroes", Bob Newhart complains that the vichyssoise tastes like potato soup. FYI footnote to the joke: Mayo Clinic Recipe: Cold potato-leek soup (vichyssoise)
In intro to his famous King Kong shtick, Newhart, volunteers that he actually served in the Army, in real life, during the Korean War:
"I said, 'Shoo ape! You're going to have to leave, sir!'"
"I thought maybe I could smear the Chrysler Building with bananas"