"Its absolutely not true that Grant was ordered not to proceed further south than Grenada. Grant had orderd Sherman south, down the Mississippi River to Vicksburg, and Sherman left the morning of 20 December. Grant was to move down the Mississippi Central Railroad and hold Pemberton in place at Grenada while Sherman "waltzed in" the back door at Vicksburg. Grant had hoped to drive Pemberton back toward Jackson and support Sherman's attack. Van Dorn's Raid spoiled the whole plan, and Sherman went down the river unsupported as Grant turned back after the raid. In fact, 4 January 1863, Sherman sent one of the great messages of the Civil War (at least in my opinion) to Grant "I have not heard a word from you since I left Oxford, and cannot undertake to describe with what painful supense I listened for the sound of your guns in the distance while we lay in the swamps of the Yazoo. Observing the heavy reenforcements pouring into Vicksburg, and not hearing from you, I was forced at lst to conclude the necessity had compelled you to fall back to Holly Springs." Official Records, Volume 17, Part 1, page 612. Now, why would Sherman have sent this message to Grant if he had not been planning on Grant coming South to support his attack?" This a note I got from Gen. Parker Hills the Historian on the Van Dorn Raid Project. Also get a copy of Vicksburg Campaing driving tour guide published by the Friends of the Vicksburg Campaign and Historic Trail an read Part 2 page 8-10. Also The Civil War A Narrative by Shelby Foote Vol. II and read about theweekes leading up to Dec 20, 1862 there were lots of things taking place like Grant sending Sherman to Memphis to take command of troops sent to Memphis to be under McClernand to move on Vicksburg. Sherman took command an moved south before McClernand arrived in Memphis and this was part of Grants plan to take Vicksburg for his own pearsonal gain.