Steve, I am no expert on this or any subject, but I am almost certain that the largest Naval concentration at one single battle or campaign was that at Fort Fisher, during the period November, 1864 to January, 1865. I do hope someone will correct me if I am wrong on this one, but I believe the answers can be found in Porter's volume or in the Naval Official Records. The attack on New Orleans in April, 1862, was in itself quite a massive concentration of Naval and supporting vessels, but I am absolutely sure that Fort Fisher was the largest ever, during the Civil War.