Following President Lincoln's declaration of a blockade of the southern coast on 19 April 1861, the US Navy moved to implement the President's orders. The blockade was initially organized as the Atlantic Blockading Squadron (Flag Officer Silas H. Stringham commanding) and the Gulf Blockading Squadron (Flag Officer William Mervine commanding). Navy warships on foreign stations were recalled, and as they arrived and were refitted, began to take up station on the blockade. The USS Niagara took up station off Charleston, SC on 10 May 1861; about two weeks later, the USS Brooklyn was off the Mississippi River mouth on 26 May. By early July Stringham had 22 warships at his disposal, and Mervine had 21.
The overall blockade strategy was set by the Commission of Conference, also referred to as the Blockade Board, under the chairmanship of Capt. Samuel F. Du Pont. The Board realized that the extensiveness of the coastline of the Confederacy was both blessing and curse. On the one hand, that extensiveness would make effective implementation of the blockade an immense task; at the same time, it would also make it difficult for the Confederacy to defend. The Board conceived of a series of amphibious operations off the Confederate Altlantic and Gulf Coasts to secure bases of operation from which the ships of the Blockade could operate.
Stringham led a squadron of six warships, two army transports and supporting vessels against Hatteras Inlet, NC in August 1861 (more on that when we get to August). The end result of this expedition was the first of many successful US Navy victories along the Confederate coast. Despite this, criticism of Stringham forced his resignation; and the Atlantic Squadron was divided into the North Atlantic Blockading Squadron, under the command of Flag Officer Louis M. Goldsborough, and the South Atlantic Blockading Squadron, under the command of Flag Officer Du Pont. The North Atlantic Squadron was responsible for the coasts of Virginia and N. Carolina, while the South Atlantic Squadron patrolled the coasts of S. Carolina, Georgia, and NE Florida down to Cape Canaveral.
By the beginning of 1862, the Gulf Squadron was similarly divided into the East Gulf Blockading Squadron, responsible for the Florida Coast from Cape Canaveral around to St. Andrew's Bay, and the West Gulf Blockading Squadron, which had the remainder of the Gulf Coast from St. Andrew's Bay to the mouth of the Rio Grande River at the US/Mexico Border. This arrangement remained throughout the rest of the war.
Tucker, Spencer C. Blue and Gray Navies. The Civil War Afloat. Annapolis: Naval Institue Press, 2006.
Simson, Jay W. Naval Strategies of the Civil War. Nashville: Cumberland House, 2001.