The "golden opportunity" so earnestly pointed out by Halleck, while not entirely lost, was nevertheless seriously diminished by the hesitation and delay of the Union commanders to agree upon some plan of effective coöperation. When, at the fall of Fort Donelson the Confederates retreated from Nashville toward Chattanooga, and from Columbus toward Jackson, a swift advance by the Tennessee River could have kept them separated; but as that open highway was not promptly followed in force, the flying Confederate detachments found abundant leisure to form a junction.
Grant reached Savannah, on the east bank of the Tennessee River, about the middle of March, and in a few days began massing troops at Pittsburg Landing, six miles farther south, on the west bank of the Tennessee; still keeping his headquarters at Savannah, to await the arrival of Buell and his army. During the next two weeks he reported several times that the enemy was concentrating at Corinth, Mississippi, an important railroad crossing twenty miles from Pittsburg Landing, the estimate of their number varying from forty to eighty thousand. All this time his mind was so filled with an eager intention to begin a march upon Corinth, and a confidence that he could win a victory by a prompt attack, that he neglected the essential precaution of providing against an attack by the enemy, which at the same time was occupying the thoughts of the Confederate commander General Johnston.
General Grant was therefore greatly surprised on the morning of April 6, when he proceeded from Savannah to Pittsburg Landing, to learn the cause of a fierce cannonade. He found that the Confederate army, forty thousand strong, was making an unexpected and determined attack in force on the Union camp, whose five divisions numbered a total of about thirty-three thousand. The Union generals had made no provision against such an attack. No intrenchments had been thrown up, no plan or understanding arranged. A few preliminary picket skirmishes had, indeed, put the Union front on the alert, but the commanders of brigades and regiments were not prepared for the impetuous rush with which the three successive Confederate lines began the main battle. On their part, the enemy did not realize their hope of effecting a complete surprise, and the nature of the ground was so characterized by a network of local roads, alternating patches of woods and open fields, miry hollows and abrupt ravines, that the lines of conflict were quickly broken into short, disjointed movements that admitted of little or no combined or systematic direction. The effort of the Union officers was necessarily limited to a continuous resistance to the advance of the enemy, from whatever direction it came; that of the Confederate leaders to the general purpose of forcing the Union lines away from Pittsburg Landing so that they might destroy the Federal transports and thus cut off all means of retreat. In this effort, although during the whole of Sunday, April 6, the Union front had been forced back a mile and a half, the enemy had not entirely succeeded. About sunset, General Beauregard, who, by the death of General Johnston during the afternoon, succeeded to the Confederate command, gave orders to suspend the attack, in the firm expectation however, that he would be able to complete his victory the next morning.
But in this hope he was disappointed. During the day the vanguard of Buell's army had arrived on the opposite bank of the river. Before nightfall one of his brigades was ferried across and deployed in front of the exultant enemy. During the night and early Monday morning three superb divisions of Buell's army, about twenty thousand fresh, well-drilled troops, were advanced to the front under Buell's own direction; and by three o'clock of that day the two wings of the Union army were once more in possession of all the ground that had been lost on the previous day, while the foiled and disorganized Confederates were in full retreat upon Corinth. The severity of the battle may be judged by the losses. In the Union army: killed, 1754; wounded, 8408; missing, 2885. In the Confederate army: killed, 1728; wounded, 8012; missing. 954.
Having comprehended the uncertainty of Buell's successful junction with Grant, Halleck must have received tidings of the final victory at Pittsburg Landing with emotions of deep satisfaction. To this was now joined the further gratifying news that the enemy on that same momentous April 7 had surrendered Island No. 10, together with six or seven thousand Confederate troops, including three general officers, to the combined operations of General Pope and Flag-Officer Foote. Full particulars of these two important victories did not reach Halleck for several days. Following previous suggestions, Pope and Foote promptly moved their gunboats and troops down the river to the next Confederate stronghold, Fort Pillow, where extensive fortifications, aided by an overflow of the adjacent river banks, indicated strong resistance and considerable delay. When all the conditions became more fully known, Halleck at length adopted the resolution, to which he had been strongly leaning for some time, to take the field himself. About April 10 he proceeded from St. Louis to Pittsburg Landing, and on the fifteenth ordered Pope with his army to join him there, which the latter, having his troops already on transports succeeded in accomplishing by April 22. Halleck immediately effected a new organization, combining the armies of the Tennessee, of the Ohio, and of the Mississippi into respectively his right wing, center, and left wing. He assumed command of the whole himself, and nominally made Grant second in command. Practically, however, he left Grant so little authority or work that the latter felt himself slighted, and asked leave to proceed to another field of duty.
It required but a few weeks to demonstrate that however high were Halleck's professional acquirements in other respects, he was totally unfit for a commander in the field. Grant had undoubtedly been careless in not providing against the enemy's attack at Pittsburg Landing. Halleck, on the other extreme, was now doubly over-cautious in his march upon Corinth. From first to last, his campaign resembled a siege. With over one hundred thousand men under his hand, he moved at a snail's pace, building roads and breastworks, and consuming more than a month in advancing a distance of twenty miles; during which period Beauregard managed to collect about fifty thousand effective Confederates and construct defensive fortifications with equal industry around Corinth. When, on May 29, Halleck was within assaulting distance of the rebel intrenchments Beauregard had leisurely removed his sick and wounded, destroyed or carried away his stores, and that night finally evacuated the place, leaving Halleck to reap, practically, a barren victory.
Nor were the general's plans and actions any more fruitful during the following six weeks. He wasted the time and energy of his soldiers multiplying useless fortifications about Corinth. He despatched Buell's wing of the army on a march toward eastern Tennessee but under such instructions and limitations that long before reaching its objective it was met by a Confederate army under General Bragg, and forced into a retrograde movement which carried it back to Louisville. More deplorable, however, than either of these errors of judgment was Halleck's neglect to seize the opportune moment when, by a vigorous movement in coöperation with the brilliant naval victories under Flag-Officer Farragut, commanding a formidable fleet of Union war-ships, he might have completed the over-shadowing military task of opening the Mississippi River.