Duddy Gunne

• Michael Gunn: manager of Gaiety Theatre, Dublin
• dead and gone
• daddy gone
• dud: a fake bullet, a duddy gun might be therefore a fake gun. Or a gun that fires blanks, suggesting impotence.
• duddy: (Scots English) ragged, tattered

also Gunne here refers to Cannon. Maybe "Sir Cannon" is the real gun with no firing problems.