A doctrinal shift took place at the same time. Prior to the war, the United States Navy emphasized single-ship operations, but the nature of the conflict soon made use of whole fleets necessary. Already at the Battle of Port Royal (7 November 1861), 77 vessels, including 19 warships, were employed. This was the largest naval expedition that had ever sailed under the U.S. flag, but the record did not stand for long. Subsequent operations at New Orleans, Mobile, and several positions in the interior confirmed the importance of large fleets in modern naval operations.