The argument over the performance of the Union commander on the nation's bloodiest day is far from settled.
Major Gen. George B. McClellan was sacked by President Abraham Lincoln less than two months after the Battle of Antietam. For more than a century, Civil War historians have written off his conduct of the battle as slow, poorly coordinated and a waste of a 2-1 numerical advantage.
But visitors taking a guided tour of the Antietam National Battlefield these days are likely to hear a more nuanced appraisal of McClellan.
Brian Baracz, a National Park Service ranger who leads tours of the battlefield, said that while McClellan might not have measured up to Robert E. Lee or Ulysses S. Grant, he did the best work of his career during the Antietam campaign.
"He's not the greatest general in the world, but he did a fair job of fighting here," Baracz said.
Modern Civil War scholarship, Baracz said, has cast doubt on the traditional estimate that McClellan had an advantage of as much as 80,000 troops against Lee's 30,000. He said the Union advantage, in terms of soldiers on the field that day, was probably more in the range of 60,000 vs. 40,000.
The ranger's presentation reflects a revisionist movement in the interpretation of McClellan's performance in general, not just as the commander of Antietam.
Among McClellan's defenders is Tom Clemens, a retired history professor at Hagerstown Community College who heads the Save Historic Antietam Foundation. He contends that by pushing Lee back to Virginia, McClellan accomplished everything he was ordered to do during the Maryland campaign. Clemens said the general's accomplishments have been minimized because he was up against two American "icons" in his military rival Lee and political antagonist Lincoln.
In Clemens' view McClellan was asked on Sept. 2 to take control of a demoralized and disorganized Army of the Potomac, routed days earlier at the Second Battle of Manassas, and to mobilize it to repel Lee's invasion.
McClellan did have a stroke of luck Sept. 13 when a Union corporal found the most famous three cigars in American history wrapped in a copy of Lee's plans for the campaign — showing how he had sent his various units in multiple directions.
The next day McClellan defeated a Confederate force at South Mountain. Some contend that the Union general moved too slowly to engage Lee after that battle, allowing the Confederate commander time to consolidate his forces and stave off disaster.
"He was presented with a golden opportunity that rarely falls to a battle commanders," said John Schildt, a Sharpsburg historian who has written about Antietam.
Three days after South Mountain, the armies met along Antietam Creek in a battle that left roughly 21,000 men killed and wounded. Two days after that, Lee crossed the Potomac and returned to Virginia. The victory allowed Lincoln to issue the Emancipation Proclamation on Sept. 22.
Mary Abroe, who teaches history at the College of Lake County in Illinois and serves on the Antietam foundation board, said scholars will probably be debating the battle at its 250th anniversary.
"Of course, they'll still be arguing about it 100 years from now," she said. "It's what we all love to do."