 The first major battle, at Mechanicsville, was poorly coordinated by Lee and his subordinates and resulted in heavy casualties for little tactical gain.However the battle had a significant impact on McClellan's nerve.The surprise appearance of Maj. Gen. Stonewall Jackson's troops in the battle (when they had last been reported to be many miles away in the Shenandoah Valley) convinced McClellan that he was even more outnumbered than he had thought.