Retreating soldiers singing

I wondered if that was the soldiers or just an audio dub from the movie makers. I thought the idea was to conceal the retreat. Thousands of men singing does not seem like stealth to me.

It may have been because the unit was meant to be from a federalized Indiana National Guard outfit, absorbed by a regular Army division for service in Korea.

More likely, the song was probably used because of it's somewhat haunting and longing "Back Home..." refrain.