Re Johnny Comes Marching Home-
Essay on Civil War Songs, Frederick Fennell (my remarks were from this, the following is direct quote).

"Patrick S. Gilmore's war record included the bandmastership of the 24th Massachusetts Volunteer Regiment, and he later served in charge of all army music under the command of General Nathaniel Banks in New Orleans. It was here in 1864 that he took an air from his old country, Ireland, one called in part Johnny, I hardly knew ye, and fashioned it with new material into a creation of his own. He chose the pseudonym Louis Lambert as the name under which to publish the song. It is strange that he would dissociate himself from what many believe to be the best song of the times, When Johnny Comes Marching Home."
The article goes on to discuss the evolution of The Battle Hymn of the Republic,.... "Our setting is rustic in comparison to today's sophisticated versions, but this is probaby how it was sung and certainly how it was played, for the band accompaniment [in this collection] is an arrangement by Patrick S. Gilmore."

Sousa regarded Gilmore as the "Father of the American Band." Gilmore was born in Ballygar, County Galway, Ireland, in 1829. He came to America bringing ideas and instrumentations from European bands. He died in 1892.

http://www.psgilmore-society.org
Also Wikipedia, etc., etc.

His lyrics for "When Johnny Comes Marching Home" are given in Wikipedia and elsewhere. His archive and collection is held at the University of Maryland.