Father Corby is perhaps the most famous of the Holy Cross priests sent to aid as chaplains during the Civil War. He was the chaplain for the 88th Regiment New York Infantry 2nd Brigade 1st Division 2nd Corps, referred to as the Irish Brigade. In the picture to the right of the chaplains for the Irish Brigade, Father Corby is seated on the right in the first row. When the men arrived at Gettysburg on the second day of fighting, the bloodiest battle of the Civil War had already been raging on. The Union army was positioned in a "fish hook" stretching from Cemetery Ridge to the peak of Little Round Top. The Irish Brigade reinforced Cemetery Ridge.

Just before the men were to enter battle, Father Corby realized he did not have enough time to hear individual confessions. He asked for the brief opportunity to give general absolution to all of the soldiers and officers. This act was common among European armies but not frequently seen on American soil. The scene has been described many times and reenacted in the movie Gettysburg.

Standing atop a large rock, Father Corby told the men they would receive absolution by making a sincere act of contrition. He ended by saying the Catholic Church refused Christian burial to soldiers who turned his back on his foe or deserted his flag. The men, who had been standing at order arms, dropped to one knee and bowed their heads. Father Corby then raised his arm and spoke the latin phrase, Dominus noster Jesus Christus vos absolvat. The scene was awe inspiring due to the sheer number of men involved and the battle scene surrounding them all.

There are two monuments at Gettysburg dedicated to Father Corby and the Irish Brigade. The first is of Father Corby giving general absolution with his arm raised and cap by his feet. The second is the Irish Brigade Monument dedicated to the 63rd, 69th, and 88th New York Infantry and 14th New York Independent Battery. The Irish cross stands with an Irish wolfhound laying at the foot of the cross.