Also in the spring of 1862, in Shenandoah Valley, Jackson led his Valley Campaign, during which he employed rapid and unpredictable movements on interior lines. Jackson's 17,000 troops marched 646 miles (1,040km) in 48 days, during which they won minor battles as they successfully engaged three Union armies, comprising 52,000 men, including those of Nathaniel P. Banks and John C. Frémont, preventing them from reinforcing the Union offensive against Richmond. The swiftness of Jackson's troops earned them the nickname foot cavalry. Johnston halted McClellan's advance at the Battle of Seven Pines, but he was wounded in the battle, and Robert E. Lee assumed his position of command. Lee and his senior subordinates, James Longstreet and Stonewall Jackson, defeated McClellan in the Seven Days Battles, forcing McClellan's retreat.