Brigadier-General John Gibbon was commanding the Iron Brigade during the Battle of Antietam on September 17, 1862. Charged with spearheading the assault through Miller’s Cornfield that morning, Gibbon posted the six Napoleons of Battery B, 4^th U.S. Light Artillery, on a nearby knoll to protect his right flank. It was not long before the exposed battery came under withering fire, and soon 40 of its 100 men had fallen to Confederate bullets. Gibbon watched as the Battery’s guns belched canister toward the rebels rattling through the corn but to no avail; the gunners had unwittingly aimed their muzzles too high and were overshooting the enemy.

As Confederate troops charged Battery B, Gibbon jumped off his horse, ran to one of the guns, and adjusted the elevating screw to depress the muzzle. Then, at the General's orders, the crew fired several rounds more, blasting away a section of the cornfield's fence - and with it the onrushing Confederates. Gibbon’s aplomb probably saved Battery B from being overrun.