The Union's strategy was devised by Winfield Scott, whose "Anaconda Plan" called for the division of the Confederacy by seizing control of the Mississippi River. One of the first steps in such operations was the imposition of the Union blockade. After the blockade was established, a Confederate naval counterattack attempted to drive off the Union navy, resulting in the Battle of the Head of Passes. The Union countermove was to enter the mouth of the Mississippi River, ascend to New Orleans and capture the city, closing off the mouth of the Mississippi to Confederate shipping both from the Gulf and from Mississippi River ports still used by Confederate vessels. In mid-January 1862, Flag Officer David G. Farragut had undertaken this enterprise with his West Gulf Blockading Squadron. The way was soon open except the water passage past the two masonry forts held by Confederate artillery, Fort Jackson and Fort St. Philip, which were above the Head of Passes approximately 70 miles (110 km) downriver below New Orleans.

The two Confederate forts on the Mississippi River south of the city were attacked by a Union Navy fleet. As long as the forts could keep the Federal forces from moving on the city, it was safe, but if they fell or were bypassed, there were no fall-back positions to impede the Union advance.

New Orleans, the largest city in the Confederacy, was already under threat of attack from its north when David Farragut moved his fleet into the river from the south. Although the Union threat from upriver was geographically more remote than that from the Gulf of Mexico, a series of losses in Kentucky and Tennessee had forced the Confederate War and Navy Departments in Richmond to strip the region of much of its defenses. Men and equipment had been withdrawn from the local defenses, so that by mid-April almost nothing remained south of the city except the two forts and an assortment of gunboats of questionable worth.^[42] Without reducing the pressure from the north, (Union) President Abraham Lincoln set in motion a combined Army-Navy operation to attack from the south. The Union Army offered 18,000 soldiers, led by the political general Benjamin F. Butler. The Navy contributed a large fraction of its West Gulf Blockading Squadron, which was commanded by Flag Officer David G. Farragut. The squadron was augmented by a semi-autonomous flotilla of mortar schooners and their support vessels under Commander David Dixon Porter.^[43]

The ensuing battle can be divided into two parts: a mostly-ineffective bombardment of the Confederate-held forts by the raft-mounted mortars, and the successful passage of the forts by much of Farragut's fleet on the night of April 24. During the passage, one Federal warship was lost and three others turned back, while the Confederate gunboats were virtually obliterated. The subsequent capture of the city, achieved with no further significant opposition, was a serious, even fatal, blow from which the Confederacy never recovered.^[44] The forts remained after the fleet had passed, but the demoralized enlisted men in Fort Jackson mutinied and forced their surrender.^[45]