Pemberton responded to the Union movements by moving his forces north along the course of the Big Black River, shadowing the Union movements, but never crossing the river. Meanwhile, reinforcements were brought up from elsewhere in the Confederacy and concentrated at Jackson. General Joseph E. Johnston was ordered on May 10 to travel to Jackson to command the growing force, which would eventually amount to about 6,000 men. One of these units was the brigade of Brigadier General John Gregg, which had been sent to Jackson from Port Hudson, Louisiana. In his only aggressive action at the time, Pemberton sent Gregg to Raymond with hopes of intercepting a Union unit rumored to be at Utica. Both Gregg and Pemberton believed that the Union force was only a single brigade, which would have numbered about 1,500 men, and that any advance against Raymond would only be a feint. In reality, the Union force at Utica was McPherson's corps, which numbered about 10,000 to 12,000 men.