"You're In the Army Now" was, IIRC1, the title song for a movie of the same title ca. mid 1940s(?). Bing Crosby and Danny Kaye I believe were the stars. (Can't remember who the girls were, but of course they were cute.)
I recall one of the neighbors having sheet music with cast pictures on the front.
I can't say whether it was written for the movie or was adapted from an earlier song.
1 At least I think I remember but it was of course a few years ago and I was quite young.