Grant's Canal (also known as Williams's Canal) was an incomplete military effort to construct a canal through De Soto Point in Louisiana, across the Mississippi River from Vicksburg, Mississippi. During the American Civil War, the Union Navy attempted to capture the Confederate-held city of Vicksburg in 1862, but were unable to do so with army support. Union Brigadier-General Thomas Williams was sent to De Soto Point with 3,200 men to dig a canal capable of bypassing the strong defenses around Vicksburg. Despite being assisted by locally enslaved people, Williams was unable to finish constructing the canal due to disease and falling river levels, and the project was abandoned until January 1863, when Union Major-General Ulysses S. Grant took an interest in the project.
Grant attempted to resolve some of the issues inherent to the concept by moving the upstream entrance to a spot with a stronger current, but the heavy rains and flooding that broke a dam prevented the project from succeeding. Work was abandoned in March, and Grant eventually used other methods to capture Vicksburg, whose Confederate garrison surrendered on July 4, 1863. In 1876, the Mississippi River changed course to cut across De Soto Point, eventually isolating Vicksburg from the river, but the completion of the Yazoo Diversion Canal in 1903 restored Vicksburg's river access. Most of the canal site has since been destroyed by agriculture, but a small section survives. This section was donated by local landowners to the National Park Service and became part of Vicksburg National Military Park in 1990. A 1974 article in The Military Engineer speculated that the canal would likely have been successful if the dam at the downstream end of the canal had been opened.