496 Grant moves to Pittsburg Landing. [isez however, had soon to give way to the march of events. An advance from south-west Missouri in December, led by General Curtis under Halleck's orders, culminated in a Federal victory at Pea Ridge, Arkansas, on March 7; and on March 9 was fought the famous naval battle between the ironclads Monitor and Merrimac in Hampton Roads, Virginia, ending in the disabling and retreat of the Confederate vessel. Under these new conditions, President Lincoln, on March 11 issued his War Order, No. 3, relieving McClellan from general command, and charging him with the conduct of the campaign against Richmond; while the same order united the three western Departments as far east as Knoxville, Tennessee, into the Department of the Mississippi, which was placed under the command of Halleck. Owing to misunderstanding, Grant was for a few days in unmerited disgrace, and came near being put under arrest; but on March 13 he was restored to the command of the Tennessee expedition, for which a con- centration of troops had been begun at Pittsburg Landing, on the west bank of the Tennessee. Three days later Halleck telegraphed to Buell, whom he could now command, to move his forces as rapidly as possible to the Tennessee to join Grant. For some days Halleck's dispatches were indefinite as to plan. Gradually, however, he indicated his intention to go himself to the Tennessee and take command, and to attack the enemy at the important railroad junction of Corinth, Mississippi, where a large force was reported to be gathering. Little by little the Union camp at Pittsburg Landing was changing its character. At the beginning of March it was intended to be merely a temporary base, from which to operate against the enemy's railroads. By the end of the month it had become an army of five divisions, 33,000 strong, with a sixth division camped a few miles to the north. All the troops were comparatively raw ; two divisions had never been under fire. Many regiments however, equally raw, had shown sufficient courage and steadiness at the capture of Fort Donelson ; and there was therefore no lack of confidence either in men or officers. But one lesson they had not yet learned that of prudence and precaution. They knew perfectly well that a large Con- federate force, estimated at from 60,000 to 80,000 men, was concentrated at Corinth ; but, their thoughts being solely intent on an advance, they made not a single defensive preparation. Sherman afterwards wrote; "At a later period of the war, we could have rendered this position impregnable in one night." In this fancied security they remained until Sunday morning, April 6, when they suddenly found themselves engaged in a desperate battle. With the hope of crushing this force before Buell could effect his junction with it, 40,000 Confederate troops, under command of General Albert Sidney Johnston, had, during the last two days, marched from Corinth, and now advanced in three lines to the attack. It was not a complete surprise; sharp picket firing had put the Federal camps on the alert,
