General Grant, in expectation that an attack in his rear would be made by General J. E. Johnston, formed a provisional corps by taking brigades from several corps, and assigned General Sherman to command it. He was sent in the direction of Big Black. Colonel Wilson, then commanding the Fifteenth Illinois Cavalry, was sent to the Big Black River to watch for the expected advance of Johnston, when Sherman was to be notified, so that he might meet and hold Johnston in check until additional reenforcements should arrive. Wilson never sent the notice. An officer of Grant's army, whose rank and position gave opportunity for accurate information, writes:
It was always a matter of surprise to Grant and his commanders that Johnston failed to make the attempt to break up the siege of Vicksburg, of which from the long line and consequent weakness of the army of the North there seemed a fair chance of accomplishment.General Johnston, being informed on the 5th of the surrender of Vicksburg, fell back to Jackson, where his army arrived on the 7th.
On the morning of the 9th the enemy appeared in heavy force in front of the works thrown up for the defense of the place; these, consisting of a line of riflepits prepared at intervals for artillery. . . . were badly located and constructed, presenting but a slight obstacle to a vigorous assault.1The weather was hot, deep dust covered the country roads, and for about ten miles there was no water to supply the troops who were advancing in heavy order of battle from Clinton; the circumstances above mentioned caused General Johnston, as he states, to expect that the enemy ‘would be compelled to make an immediate assault.’ Sherman, in command of the attacking column, did not, however, elect to assault the entrenchments, but moved the left of his line around so as to rest upon Pearl River above, and then, extending his right so as to reach the river below, commenced entrenching a line of investment. As early as May 27th Brigadier General J. G. Rains had been directed to report to General Johnston in connection with torpedoes and sub-terra shells, and a request had been made for ‘all reasonable facilities and aid in the supply of men or material for the fair trial of his torpedoes and shells.’ There could scarcely have been presented a better opportunity for their use than that offered by the heavy column marching against Jackson, and the enemy would have been taken at great disadvantage if our troops had met them midway between Jackson and Clinton. As the defenses of Jackson had not been so corrected in location and increased in strength as to avail against anything other than a mere assault, it is