I wish I had a clear timeline. Here is the reference.
". . . an incident occurred, which I have never seen recorded, but which seems to me worthy of not. A vessel suddenly appeared through the mist from behind the Bar, a passenger steamer, which was made out to be the Nashville. She had no colors set, and as she approached the fleet she refused to show them. Captain Faunce ordered one of the guns manned, and as she came still nearer turned to the gunner. 'Stop her!' he said, and a shot went skipping across her bows. Immediately the United States ensign went to her gaff end, and she was allowed to proceed. The Harriet Lane had fired the first shotted gun from the Union side."
Civil War correspondent, G. S. Osbon