I was thinking along those lines too ,Martin. I seem to remember that he called it "Of to join the column in the morning".It was a long time ago and the ol' memory is not what it used to be !.An old friend of my father's and his brother was a man called Peter Daly,who subsequently went on to become Commandant of The International Brigade in the Spanish Civil War and died there, was nicknamed "Column". This was due to the story that when he and my Uncle were among a group picked up and held in Wexford Barracks he walked out of the barracks with visitors who had come to say goodbye to their sons before they were transferred to ,in their case Kilmainham, initially .The story goes that when Pater was picked up on Wexford Quays a few minutes later he was whistling "Of to join The Column". Hence the name.How true that story is I don't know but it seems to indicate that the song was around in the 1920s.