 Longstreet's actions in the final two major Confederate defensive battles of 1862 would be the proving grounds for his development of dominant defensive tactics. In the Maryland Campaign of September, at the Battle of Antietam, Longstreet held his part of the Confederate defensive line against Union forces twice as numerous. After the delaying action Longstreet's corps fought at South Mountain, he retired to Sharpsburg to join Stonewall Jackson, and prepared to fight a defensive battle. Using terrain to his advantage, Longstreet validated his idea that the tactical defense was now vastly superior to the exposed offense. While the offense dominated in the time of Napoleon, the technological advancements had overturned this. Lt. Col. Harold M. Knudsen claims that Longstreet was one of the few Civil War officers truly aware of this. At the end of that bloodiest day of the Civil War, Lee greeted his subordinate by saying, "Ah! Here is Longstreet; here's my old war-horse!" On October 9, a few weeks after Antietam, Longstreet was promoted to lieutenant general. Lee arranged for Longstreet's promotion to be dated one day earlier than Jackson's, making the Old War-Horse the senior lieutenant general in the entire Confederate Army. In an army reorganization in November, Longstreet's command, now designated the First Corps, consisted of five divisions, approximately 41,000 men.
