In 1863, the unit was transferred to Grand Gulf, Mississippi, a key point on the Mississippi River. After Major General Ulysses S. Grant landed Union infantry at Bruinsburg, Landis's Battery formed part of Confederate defenses at the battles of Port Gibson in early May, after which Landis was promoted and Lieutenant John M. Langan took command. Later that month, it took part in the Battle of Champion Hill. On May 17, the battery was part of a Confederate force tasked with holding the crossing of the Big Black River at the Battle of Big Black River Bridge, where it may have suffered the capture of two cannons. Landis's Battery next saw action during the siege of Vicksburg. While there, the battery helped repulse Union assaults on May 22. Landis's Battery was captured when the Confederate garrison of Vicksburg surrendered on July 4. Although the surviving men of the battery were exchanged, the battery was not reorganized after Vicksburg; instead, it was absorbed into Guibor's Missouri Battery along with Wade's Missouri Battery.