During the early part of the Civil War, Lander served with distinction on secret missions as a volunteer aide de camp on the staff of General McClellan. He was promoted to brigadier general of volunteers on May 17, 1861 and served on the staff of General Thomas A. Morris during the battles of Philippi and Rich Mountain and many minor skirmishes. Lander published a popular poem on the Battle of Ball's Bluff, as well as several other patriotic poems that drew national attention.