Jackson's orders from Johnston were to avoid general combat because he was seriously outnumbered, but at the same time he was to keep Banks occupied enough to prevent the detachment of troops to reinforce McClellan on the Peninsula. Receiving incorrect intelligence, Banks concluded that Jackson had left the Valley, and he proceeded to move east, back to the vicinity of Washington. Jackson was dismayed at this movement because Banks was doing exactly what Jackson had been directed to prevent. When Ashby reported that only a few infantry regiments and some artillery of Banks's corps remained at Winchester, Jackson decided to attack the Union detachment in an attempt to force the remainder of Banks's corps to return. But Ashby's information was incorrect; actually, an entire Union division was still stationed in the town. At the First Battle of Kernstown (March 23, 1862), fought a few miles south of Winchester, the Federals stopped Jackson's advance and then counterattacked, turning his left flank and forcing him to retreat. Although a tactical defeat for Jackson, his only defeat during the campaign, it was a strategic victory for the Confederacy, forcing President Lincoln to keep Banks's forces in the Valley and McDowell's 30,000-man corps near Fredericksburg, subtracting about 50,000 soldiers from McClellan's Peninsula invasion force.