Background
"When Johnny Comes Marching Home" (sometimes "When Johnny Comes Marching Home Again") is a popular song of the American Civil War that expressed people's longing for the return of their friends and relatives who were fighting in the war.

Some believe the tune is that of the Irish antiwar song "Johnny I Hardly Knew Ye", presumed to be the original on the basis of oral and textual evidence, although no published version is known to pre-date "When Johnny Comes Marching Home Again" [1]. However, expert James Fuld, author of the standard text on popular music, The Book of World Famous Music, states on page 640 of that volume that Donal O'Sullivan, the Irish authority, has written the Library of Congress that he does not consider the melody of "When Johnny Comes Marching Home" as Irish in origin. As stated, no printed music of Irish origin has been discovered that predates American publication in September of 1863 by Henry Tolman in Boston under the title "When Johnny Comes Marching Home". Library of Congress records do show a title "Johnny Fill Up The Bowl" that was published in July of 1863 by John J. Daly that appears to contain the song's melody.

The lyrics, written by Irish-American bandleader Patrick Gilmore, and published under the pseudonym 'Louis Lambert', effectively reverse those of "Johnny I Hardly Knew Ye", in which Johnny returns home blind and crippled, to the woman he abandoned in order to join the army. The "Johnny" so longed for in the song is Patrick Gilmore's future brother in-law a Union Light Artillery Captain named John O'Rourke. The song was written by Patrick for his sister Annie Gilmore as she longed for the safe return of her Captain from the Civil War.