With Carolina eliminated, and eager to determine what lay ahead of him, Pakenham directed a major probe of the U.S. defenses. By giving the appearance of a full-scale attack—without intending to bring on a general engagement—Pakenham hoped Jackson would commit his forces and reveal his dispositions and strength. His staff could use the intelligence to plan a deliberate attack once the rest of the British infantry and artillery arrived. Late on the afternoon of 27 December, Pakenham’s light infantry drove the American pickets back and occupied de la Ronde and Bienvenu Plantations. There, he discovered that U.S. artillery and retreating infantry had already destroyed many of the buildings to clear fields of fire in front of their main line.
The demonstration began as soon as the early morning mist cleared. About three thousand British troops advanced across the cane-stubble fields in two columns with skirmishers from the light infantry and 95th Rifle Corps companies deployed in front of and between them. Maj. Gen. Samuel Gibbs led the 2nd Brigade, or Right Column, which advanced along the edge of the cypress swamp with the 4th, 21st, and 44th Regiments of Foot and the 1st West India Regiment toward the American left. Keane led the 3d Brigade, or Left Column, as the 85th Foot, 93d Highland Regiment, and 5th West India Regiment advanced along the river and the levee road against Jackson’s right. With continual supporting cannon and rocket fire, the infantrymen drove the remaining pickets of Maj. Henry D. Peire’s 7th Infantry and Hind’s dragoons off the Chalmette Plantation and back to the main U.S. defenses. However, the green militia did not panic at the sight of tight, disciplined columns of bayonet-wielding troops.
When Keane’s column drew within six hundred yards of the American right, four U.S. artillery batteries engaged it in front, while the guns of Louisiana fired into its flank, inflicting serious loss. After the British infantry took shelter in shallow ditches and hastily built earthworks, their own light artillery came forward and went into action to silence the U.S. batteries. The troops noted the water-filled ditch but could not determine if it was fordable.
About one thousand yards from the river, where Louisiana’s guns could not engage them, the men of Gibbs’ brigade made good progress toward the American left. They saw that the ditch in front of General Carroll’s division of Tennessee militia was dry and that the breastworks were unfinished. Lt. Col. Robert Rennie’s light infantry, advancing through the swamp on Gibbs’ flank, succeeded in driving back the American outposts. Carroll sent Lt. Col. James Henderson with a battalion of Tennesseans in an attempt to encircle them, but the British drove them back with several wounded and a number of killed, including Henderson. Nevertheless, with Keane’s brigade pinned down and several of his artillery pieces destroyed or damaged by effective counterbattery fire, Pakenham halted the advance. Some of the more exposed forward British troops waited to retreat under cover of darkness. After falling back, the British began constructing new artillery positions and repairing their damaged pieces. The action had cost the British 152 killed, wounded, or captured, against 8 dead and 8 wounded Americans. Based on the experience, the British commander decided to wait for the last of his infantry and artillery to arrive, and he requested that the Royal Navy provide him with more naval cannon. Pakenham wanted to ensure success by massing as much heavy ordnance as possible to overwhelm the U.S. batteries and to breach the earthworks.
The Americans meanwhile strengthened Line Jackson. To give the east bank defenses more depth, Louisiana militiamen began working on Line Dupre, about one-half mile behind Line Jackson, and Line Montreuil, another one and one-quarter mile farther upriver. On the west bank, a brigade of Louisiana militiamen under General Morgan’s command established Line Boisgervais. In addition, Patterson’s sailors removed most of the naval guns from Louisiana and positioned them in a “marine battery” along the riverfront, where they could fire across the Mississippi and into the flanks of a British army advance.