The Battle of Chickasaw Bayou, also called the Battle of Walnut Hills, fought December 26–29, 1862, is the opening engagement of the Vicksburg Campaign during the American Civil War.

Confederate forces under Lt. Gen. John C. Pemberton repuls an advance by Union Maj. Gen. William T. Sherman that is intended to lead to the capture of Vicksburg, Mississippi.

On December 26, three Union divisions under Sherman disembark  at Johnson's Plantation on the Yazoo River to approach the Vicksburg defenses from the northeast while a fourth lands farther upstream on December 27.

On December 27, the Federals push  their lines forward through the swamps toward the Walnut Hills, which are strongly defended.

On December 28, several futile attempts are made to get around these defenses.

On December 29, Sherman orders a frontal assault, which is repulsed with heavy casualties, then withdraw.

This Confederate victory frustrates Maj. Gen. Ulysses S. Grant's attempts to take Vicksburg by a direct approach.