in mid-June, Jackson and his troops were called to join Robert E. Lee's Army of Northern Virginia in defense of the capital. By utilizing a railroad tunnel under the Blue Ridge Mountains and then transporting troops to Hanover County on the Virginia Central Railroad, Jackson and his forces made a surprise appearance in front of McClellan at Mechanicsville. Reports had last placed Jackson's forces in the Shenandoah Valley; their presence near Richmond added greatly to the Union commander's overestimation of the strength and numbers of the forces before him. This proved a crucial factor in McClellan's decision to re-establish his base at a point many miles downstream from Richmond on the James River at Harrison's Landing, essentially a retreat that ended the Peninsula Campaign and prolonged the war almost three more years. Jackson's troops served well under Lee in the series of battles known as the Seven Days Battles, but Jackson's own performance in those battles is generally considered to be poor. He arrived late at Mechanicsville and inexplicably ordered his men to bivouac for the night within clear earshot of the battle. He was late at Savage's Station. At White Oak Swamp he failed to employ fording places to cross White Oak Swamp Creek, attempting for hours to rebuild a bridge, which limited his involvement to an ineffectual artillery duel and a missed opportunity to intervene decisively at the Battle of Glendale, which was raging nearby. At Malvern Hill Jackson participated in the futile, piecemeal frontal assaults against entrenched Union infantry and massed artillery, and suffered heavy casualties (but this was a problem for all of Lee's army in that ill-considered battle). The reasons for Jackson's sluggish and poorly coordinated actions during the Seven Days are disputed, although a severe lack of sleep after the grueling march and railroad trip from the Shenandoah Valley was probably a significant factor. Both Jackson and his troops were completely exhausted. An explanation for this and other lapses by Jackson was tersely offered by his colleague and brother in-law General Daniel Harvey Hill: "Jackson's genius never shone when he was under the command of another." Second Bull Run to Fredericksburg The military reputations of Lee's corps commanders are often characterized as Stonewall Jackson representing the audacious, offensive component of Lee's army, whereas his counterpart, James Longstreet, more typically advocated and executed defensive strategies and tactics. Jackson has been described as the army's hammer,