"Pete" Longstreet and staff
"The enemy had made three desperate attempts to capture us, the last time coming within ten or fifteen feet of our guns. It was at this time that General Gibbon, seeing the condition of the battery, came to the gun that stood in the pike, and in full uniform of a brigadier general, worked as a gunner and cannoneer. He was very conspicuous, and it is indeed surprising that he came away alive." John Cook, Battery B, 4th U.S. Artillery, Doubleday's Division
"Bullets, shot and shell whistled and screamed around us, wounded men came to the rear in large numbers, and the six Napoleon guns of Battery "B" hurled forth destruction in double rounds of canister as the enemy in increased numbers rushed forward to capture the guns. He seemed to be making headway against our troops in the cornfield to our left and the piece on the pike was firing in that direction. The gun was on a part of the road which sloped towards us and every time it went off it recoiled a great distance down the slope. In the midst of this pandemonium I happened to look at this gun and noticed that the cannoneers had carelessly allowed the elevation screw to run down and every time the piece was fired its elevation was increased until now its missiles were harmlessly thrown high over the heads of the enemy in its front. I yelled to the gunner to run up his elevating screw, but in the din he could not hear me. I jumped from my horse, rapidly ran up the elevating screw until the nozzle pointed almost into the ground in front and then nodded to the gunner to pull his lanyard. The discharge carried away most of the fence in front of it and produced great destruction in the enemy's ranks as did the subsequent discharges." BG John Gibbon, brigade commander, Army of the Potomac
Quoted in Voices of the Civil War: Antietam, Time-Life Books, Alexandria, VA, 1996, p. 74-5.
"Limping about in carpet slippers and gesturing with an unlighted cigar, he [Longstreet] ordered gun crew after gun crew to put their pieces in action along the ridge where Hill was forming his thin new line. As fast as these guns came into the open, the powerful Union batteries took them under fire from across the way, exploding caissons and mangling cannoneers. Observing one section of guns whose fire was weak because there were too few survivors to serve them properly, Old Pete dismounted his staff and improvised two high-ranking gun crews, himself holding their horses and correcting the ranges while they fired." The Civil War: a Narrative: Fort Sumter to Perryville, Shelby Foote, Vintage Books, Random House, NY, 1986, p. 694.
"As the men of Miller's gun crews [Captain M. B. Miller, Washington (LA) Artillery] fell one by one, General Longstreet, wearing a bedroom slipper on a sorely blistered foot, ordered his staff to fill in." Voices: Antietam, p. 116.
"When Miller became short-handed, by reason of his loss of cannoneers, the staff officers of Gen. Longstreet, Majors Sorrel, Fairfax, and Thomas Walton, dismounted from their horses and helped work the guns. Sorrel and Walton were wounded, and the horse of Fairfax was killed. Gen. Longstreet directed the fire of the guns in person, and by example animated the soldiers near him." Lt. William M. Owen, Washington (LA) Artillery; Voices: Antietam, p. 116-117
Edit - It is interesting to learn that Generals Gibbon and Longstreet, together with members of Longstreet's staff, helped to man cannons during the battle. One of the main purposes of the trivia game is to help people learn things they didn't know before, so for that purpose, this was a good question.
For the purpose of scoring the players' answers, it wasn't so good. It's clear that many players were unsure what was meant by "high-ranking."
The official answer names Gen. Gibbon, Gen. Longstreet, and Majors Sorrel, Fairfax, and Walton, so the questioner apparently considered the rank of major to be high-ranking. However, there were a good many other artillery officers at that battle who held the rank of major or higher.
Since the official answer doesn't name every artillery officer with a rank of major or higher, I can't deny credit to players whose answers didn't name them all, either. Everyone who submitted a response to this question will get credit for a correct answer.