It's the Dutch Tavern. Great spot. Family favorite for us. Great burgers, very good chili, nice Guinness pour and cool pinball machine. One of the oldest buildings in New London because that little block was one of very few areas that did not get burned to the ground during the American Revolution. IIRC O'Neil is said to have hung out occasionally in whatever establishment was there at the time he was around, but I don't believe it was the Dutch Tavern then.
The present owner, Peter, was in the legendary regional band the Reducers. Very good guy.