Lastly, deep raids by conventional cavalry forces were often considered 'irregular' in nature. The "Partisan Brigades" of Nathan Bedford Forrest and John Hunt Morgan operated as part of the cavalry forces of the Confederate Army of Tennessee in 1862 and 1863. They were given specific missions to destroy logistical hubs, railroad bridges, and other strategic targets to support the greater mission of the Army of Tennessee. By mid-1863, with the destruction of Morgan's raiders during the Great Raid of 1863, the Confederacy conducted few deep cavalry raids in the latter years of the war, mostly because of the losses in experienced horsemen and the offensive operations of the Union army. Federal cavalry conducted several successful raids during the war but in general used their cavalry forces in a more conventional role. A good exception was the 1863 Grierson's Raid, which did much to set the stage for General Ulysses S. Grant's victory during the Vicksburg Campaign.