At the end of March Grant took a memorable determination to transfer his whole force to the south of Vicksburg and approach it from that direction. He was urged by Sherman to give up any further attempt to use the river, and, instead, to bring his whole army back to Memphis and begin a necessarily slow approach on Vicksburg by the railway. He declared himself that on ordinary grounds of military prudence this would have been the proper course, but he decided for himself that the depressing effect of the retreat to Memphis would be politically disastrous. At Grand Gulf, 30 miles south of Vicksburg, the South possessed another fortified post on the river; to reach this Grant required the help of the Navy, not only in crossing from the western bank of the river, but in transporting the supplies for which the roads west of the river were inadequate. Admiral Porter, with his gunboats and laden barges, successfully ran the gauntlet of the Vicksburg batteries by night without serious damage. Grand Gulf was taken on May 3, and Grant's army established at this new base. A further doubt now arose. General Banks in Louisiana was at this time preparing to besiege Port Hudson. It might be well for Grant to go south and join him, and, after reducing Port Hudson, return with Banks' forces against Vicksburg. This was what now commended itself to Lincoln. In the letter of congratulation which some time later he was able to send to Grant, after referring to his former opinion which had been right, he confessed that he had now been wrong. Banks was not yet ready to move, and Vicksburg, now seriously threatened, might soon be reinforced. Orders to join Banks, though they were probably meant to be discretionary, were actually sent to Grant, but too late. He had cut himself loose from his base at Grand Gulf and marched his troops north, to live with great hardship to themselves on the country and the supplies they could take with them. He had with him 35,000 men. General Pemberton, to whom he had so far been opposed, lay covering Vicksburg with 20,000 and a further force in the city; Joseph Johnston, whom he afterwards described as the Southern general who in all the war gave him most trouble, had been sent by Jefferson Davis to take supreme command in the West, and had collected 11,000 men at Jackson, the capital of Mississippi, 45 miles east of Vicksburg. Grant was able to take his enemy in detail. Having broken up Johnston's force he defeated Pemberton in a series of battles. His victory at Champion's Hill on May 16, not a fortnight after Chancellorsville, conveyed to his mind the assurance that the North would win the war. An assault on Vicksburg failed with heavy loss. Pemberton was at last closely invested in Vicksburg and Grant could establish safe communications with the North by way of the lower Yazoo and up the Mississippi above its mouth. There had been dissension between Pemberton and Johnston, who, seeing that gunboats