Yes, Guest, Jay, that's correct about 1949.

As regards the author, I found this on the web:
In Songs of the County Down, by Cathal O'Doyle, the author is given as Canon Charles O'Neill, a parish priest of Kilcoo and later Newcastle. "In 1919 he went to Dublin and attended a sitting of the first Dáil Éireann (Irish Parliament). He was moved by the number of members whose names were answered during roll call by "faoi ghlas ag na Gaill" (locked up by foreigners) and resolved to write a song in commemoration of the Easter Rebellion".

The music is from a manuscript that was in possession of Kathleen Dallat of Ballycastle. That manuscript gives Carl Hardebeck as the arranger. It was recorded in 1913 by John McCormack. (from www.cormacbreatnach.com/the_foggy_dew_2006.asp I presume the piece recorded by McCormack was the manuscript music)

We play it occasionally at sessions. I like the song (though both my grandfathers were in the British army at that time and several of their cousins were killed close to Suvla Bay).

Don