Dugan is probably the most colorful of the Commandos. Before acquiring his dubious nickname, he was Timothy Aloysius Cadwallader, a Boston native who worked as a circus strongman before joining the British Army. He was invited to become second-in-command of the Howling Commandos after helping Nick Fury and Happy Sam Sawyer out of a Nazi-filled jam. Dugan lacks superpowers, but he's very strong, and quite good with a rifle. He also wears a bowler hat. Perhaps if he throws it hard enough, he can kill people with it. It's a perfect role for McDonough, though fans already seem miffed he's not a redhead.
Captain America won't just have Dum Dum for back-up. Last week, Hayley Atwell confirmed to Leicester Square TV that Tommy Lee Jones has indeed joined the cast. His role is still unknown, but I'm willing to bet he's playing the leader and recruiter of the Commandos, the gruff and gray Sam Sawyer. Between Jones, Samuel L. Jackson, and McDonough, I'm not sure why you'd need Steve Rogers. If I was a Nazi, I would have surrendered at the sight of that threesome alone.