Artillery at the Trostle Farm
The disaster that engulfed Sickles’ III Corps now threatened the Federal center. Meade and Hancock rushed reinforcements in the form of V Corps and much of II Corps. The tip of the Sickle’s salient at Sherfy’s Peach Orchard manned by Graham’s brigade of David Birney’s division was overwhelmed and retreated in disorder. Once “the angle had been breached, the lines connecting to it on the east and north were doomed.”  This exposed the left of Humphery’s division and it too was forced to retreat under heavy pressure sustaining heavy casualties. The final collapse of Humphrey’s division a large gap opened in the Federal lines between the elements of V Corps fighting along Devil’s Den and Little Round Top and II Corps along the central portion of Cemetery Ridge.
When Meade realized the seriousness of the situation he gave Sickles’ free reign to call for reinforcements from Harry Hunt’s Artillery Reserve as III Corps had only batteries organic to it. Those five batteries were in the think of the fighting providing invaluable support to Sickles’ hard pressed and outnumbered corps. Firing canister they cut swaths of death and destruction through the massed ranks of wildly cheering Confederates of Kershaw and Semmes and Barkdale’s brigades of McLaws’ division.
The Confederates believed that they had cut the Union line in half and advanced through the Peach Orchard and across the Wheat Field toward Cemetery Ridge.
Among the artillery called into action was the First Volunteer Brigade under the command of Lieutenant Colonel Freeman McGilvery. McGilvery, a Maine native was a former sea captain who had organized and commanded the 6th Maine Battery at the beginning of the war. He commanded it with distinction in a number of engagements. Promoted to Major in early 1863 he assumed command of the Brigade and fought at Chancellorsville and was promoted to Lieutenant Colonel in June as the Army of the Potomac pursued Lee’s Army.
McGilvery rode into the maelstrom of the retreating III Corps soldiers and broken guns. His horse was hit four times but he remained unwounded despite “exposing himself to enemy missiles on all parts of the field from Cemetery Ridge to the Peach Orchard.”  He noted that there was no infantry anywhere that could plug the gap and acted instantly on his own authority to make a decision that likely saved the Union line. In the confusion of III Corps disintegration three of his batteries had withdrawn leaving Captain John Bigelow’s 9th Massachusetts battery alone at the Trostle farm telling them they must “hold at all hazards.”  Bigelow later explained that McGilvery said that “for 4 or 500 yards in my rear there were no Union troops.” He was then instructed by McGilvery “For heavens [sic] sake hold that line…until he could get some other batteries in position…”  In another account Bigelow recorded “Captain Bigelow…there is not an infantryman back of you along the whole line which Sickles moved out; you must remain where you are and hold your position at all hazards, and sacrifice your battery if need be, until at least I can find some batteries to put in position and cover you.” 
The order could have been considered suicidal; the 21st Mississippi was nearly upon them and they were but one battery and barely one hundred troops. Bigelow did not hesitate to obey; he brought his guns into line at the Trostle house “facing one section slightly to the southwest and the other two sections directly into the path of the oncoming Confederates.” 
Bigelow’s artillerymen fought like demons he described the effect of his fire on Kershaw’s South Carolinians “the Battery immediately enfiladed them with a rapid fire of canister, which tore through their ranks and sprinkled the field with their dead and wound, until they disappeared in the woods on our left, apparently a mob.”  They poured a merciless stream of fire into the advancing Confederates until “they had exhausted their supply of canister and the enemy began to close in on his flanks.”  A German born gunner noted “we mowed them down like grass, but they were thick and rushed up.”  A hand to hand fight ensued among the guns but the Massachusetts men escaped losing 28 of its 104 men engaged, the brave commander Bigelow was wounded and nearly captured but one of his men helped him to the rear.
Their sacrifice was not in vain. They bought McGilvery an additional 30 minutes to set up a line of guns along Plum Run. Hunt praised the battery “As the battery had sacrificed itself for the safety of the line, its work is specially noticed as typical of the service that artillery is not infrequently called to render, and did render in other instances at Gettysburg besides this one.”
Bigelow’s Map of the Action at Trostle Farm
Barksdale’s brigade did not pause and continued in their relentless advance towards Cemetery Ridge, sweeping Union stragglers up as they moved forward led by their irrepressible Colonel. Before them was McGilvery’s new line, hastily cobbled together from any batteries and guns that he could find. Initially composed of 13-15 guns of four different batteries he was joined by two more batteries giving him about 25 guns in all. Subjected to intense Confederate artillery fire and infantry attacks his guns held on even as their numbers were reduced until only six guns remained operational. “Expertly directed by McGilvery a few stouthearted artillerymen continued to blaze away and keep the low bushes in front of them clear of lurking sharpshooters. Although they had no infantry supports, they somehow managed to create the illusion that the woods to their rear were filled with them, and they closed the breach until the Union high command could bring up reinforcements.” 
The reinforcements came in the form of Colonel George Willard’s “Harper’s Ferry” Brigade which was looking for revenge and redemption. This unit hit Barksdale’s now disorganized force which had reached its cumulating point hard. Willard was killed and Barksdale mortally wounded and captured in the violent clash which spelled the end of one of the greatest threats to the Union line of the entire battle. Philip Tucker in his book Barksdale’s Charge: The True High Tide of the Confederacy at Gettysburg, July 2, 1863 refers to Barksdale’s charge as the real “high water mark of the Confederacy.”
Plum Run Line
However it was McGilvery who recognized the emergency confronting the line and on his own took responsibility to rectify the situation. He courageously risked “his career in assuming authority beyond his rank”  and without his quick action, courage under fire and expert direction of his guns Barksdale’s men might have completed the breakthrough that could have won the battle for General Lee despite all of the mistakes committed by his senior leaders that day.
It was another example of an officer who had the trust of his superiors who did the right thing at the right time. It is an example of an officer used the principles of what we today call Mission Command to decisively impact a battle. McGilvery rose higher in the Federal service and was promoted to Colonel and command of the artillery of X Corps. He was slightly wounded in a finger at the battle of Deep Bottom in August 1864. The wound did not heal properly so surgeon’s decided to amputate the finger. However they administered a lethal dose of chloroform anesthesia and he died on September 9th, the Union losing one its finest artillerymen. He was buried in his native Maine and the State legislature designated the first Saturday in September as Colonel Freeman McGilvery Day in 2001.
 Trudeau, Noah Andre Gettysburg: A Testing of Courage Harper Collins, New York 2002 p.368
 Coco, Gregory A A Concise Guide to the Artillery at Gettysburg Colecraft Industries, Orrtanna PA 1998 p.31
 Hunt, Henry I Proceeded to Cemetery Hill in Battles and Leaders of the Civil War Bradford, Ned editor, Meridian Books, New York 1956 p.378
 Guelzo, Allen C Gettysburg, The Last Invasion Vintage Books, a Division of Random House, New York 2013 p.314
 Ibid. Trudeau p.385
 Bigelow, The Peach Orchard, 54; History of the Fifth, 638 retrieved from WE SAVED THE LINE FROM BEING BROKEN: Freeman McGilvery, John Bigelow, Charles Reed and the Battle of Gettysburg by Eric Campbell http://www.nps.gov/history/history/online_books/gett/gettysburg_seminars/5/essay4.htm#52
 Coddington, Edwin. The Gettysburg Campaign: A Study in Command Touchstone Books, New York 1960 p.416
 Ibid. Guelzo pp.314-315
 Ibid Hunt p.379
 Ibid. Hunt. P.379
 Ibid. Coddington p.417.
 Ibid. Coddington.