A favorite song of British soldiers during WWI, but thought to be a French army tune from the 1830s.  The earliest known version tells the story of an innkeeper's daughter, Mademoiselle de Bar le Luc.  It also became a tune of the Franco-Prussia war of 1870.  A comment offering additional lyrics:  Just blow your nose and dry your tears, we'll all be back in a few more years.

With footage from the film They Shall Not Grow Old: