Bruce Catton writes in Mr. Lincoln's Army that, "This was a deeply sentimental army, and it sang a great deal; not stirring patriotic songs, full of rally-round-the-flag heroism - they were for stay-at-home civilians - but slow, sad tunes that could express the loneliness and homesickness of boys who had been uprooted and sent out to face hardship and danger and death. Their favorite was a song called 'When This Cruel War is Over,' by Charles Carroll Sawyer....Men would sing that song and cry. More than any other possession of the army, it expressed the deep inner feeling of the boys who had gone to war so blithely in an age when no one would speak the truth about the realities of war."
Bell Wiley chimes in in Life of Billy Yank, "An impressive proportion of war favorites had extremely doleful notes, but this does not necessarily mean that the ranks were filled with melancholy soldiers. Paradoxical as it may seem, carefree campaigners apparently derived satisfaction from dwelling on themes of suffering and death, enjoying their misery as it were, and emerging from excursions into gloom with hearts lighter than before."
That said, Wiley notes that there were many ribald and vulgar songs such as a twist on the ballad "Joe Bowers." That said, they are far more often referenced than actually written out, which is frustrating to those like me who want to know what the soldiers sang about when they weren't being so darn melancholy.
I just find it hard to believe that ALL they sang were super sad songs....I mean, we are talking about 21-year-old boys away from home and women for extended periods of time.....but maybe I have too much of a 21st Century frame of mind.