Vicksburg, Mississippi, was a key position in the Confederacy both economically and militarily. The Union had made several unsuccessful attempts to take the city in the first two years of the war. Ulysses S. Grant’s final attempt was a risky flanking maneuver in which the Union army had no lines of supply and was fully dependent on living off the land in enemy territory, a previously untried approach. This article argues that Confederate impressment policy created large excess supplies in the rural areas that Grant invaded and created supply shortages in the military depot city of Vicksburg. Impressment therefore facilitated Grant’s novel invasion strategy and made the Confederate position inside Vicksburg untenable under his siege.