The day after the Battle of New Orleans, a British squadron—consisting of a sloop-of-war, a gun-brig, a schooner, and two bomb vessels—approached Fort St. Philip. The fort, which was built on the foundation of an old Spanish work at Plaquemines Bend on the east bank of the Mississippi River, had its position strengthened in recent weeks by Jackson’s engineers and artillerists. Maj. Walter H. Overton commanded the post whose armament consisted of twenty nine 24-pounder guns, a 6-pounder cannon, eight 5½-inch howitzers, and one 13-inch mortar in the fort and two 32-pounders in an earthen battery at water level. Two companies of regular artillerymen, two companies from the 7th Infantry, and two of Louisiana volunteer militia, including one of Free Men of Color, manned the post, while a U.S. Navy gunboat lay offshore.
At 3:00 p.m. on 9 January, British barges were taking soundings of the river bottom about one and one-half miles below the fort when the Americans opened fire with their cannons. Although they drove the scouts back, the artillerymen had revealed the maximum range of their guns. The British ships anchored a safe 3,960 yards below the fort, and their two bomb vessels opened fire with mortars. Problems with fuses and ammunition rendered the U.S. mortar incapable of counterbattery fire, and consequently the garrison hunkered down as it waited for the British to approach close enough to engage. The shelling continued into the night. Several armed launches pulled close to the fort firing grape and round shot from their bow guns as a diversion for the larger vessels. When the British ships closed the range, however, U.S. artillery fire drove them back. The bombardment continued intermittently for the next eight days. When the garrison received a fresh supply of ammunition and fuses for the piece, the fort’s mortar went into action. Its fire effectively disrupted the British formation. Just after dawn on 18 January, the British weighed anchor and retreated downriver. The Americans suffered two dead and seven wounded, while the British reported no casualties.
Meanwhile, back at the Chalmette Plantation, the two sides exchanged prisoners, and on the evening of 18 January, the British completed their withdrawal from the battlefield, leaving behind fourteen spiked artillery pieces. The retreat was executed in such secrecy that Jackson did not learn of it until the next day when a British doctor approached with a letter from Lambert asking the Americans to care for eighty patients too badly wounded to make the journey to the fleet. By the evening of 27 January, all the landing forces had re embarked.
Undeterred, Admiral Cochrane decided to revert to the earlier plan to take New Orleans by moving overland from Mobile. He dispatched a messenger to Colonel Nicholls at Apalachicola with orders to send one force of Indian allies northeast to raid the Georgia frontier and another northwest to cut off Fort Stoddert and the communities north of Mobile. Cochrane’s fleet would attack up Mobile Bay and put Lambert’s army ashore to capture Fort Bowyer before marching from Mobile to Baton Rouge. After cutting New Orleans off from the rest of the United States, the army would entrench and wait for Jackson’s army to attack—turning the tables of 8 January.