Doughboy Jack and Doughnut Jill
I've done period and ethnic dance programs and classes all my life, starting with Bavarian and Austrian and finally all the nations that produced arms and warred with each other throughout the last century. The dances I do parallel the firearms I collect.
Every program or class lets me take a fresh look at my field. I was developing a unique USO dance program for Veteran's Day last year when I stumbled on an old recording called "Doughboy Jack and Doughnut Jill" from WWI. Sexy title don't you think? Of course, the recording was exactly what you would expect, an oldtime sounding band and vocal but perfect for my use.
That still doesn't give us the origin of the term but it does pull you to the time as surely as an old pistol or rifle will. If anyone wants a link to the tune drop me a line and I'll get it to you.
If you found the Welch song "Men of Harlech" sung by the British troops at Rourke's Drift in the film "Zulu" a perfect example of courage under fire I can connect you to that too, plus lots of research material on the actual events. Then, too, how about original versions of "Lili Marleen" and other WWII barracks and trench favorites of the belligerants on both sides?
Herb Fredricksen