Brigadier General Thomas F. Meagher (pronounced "marr") was in command of the famous "Irish Brigade" of Richardson's First Division, II Corps. The Brigade consisted of the heavily Irish 63rd (Col. John Burke), "Fighting 69th" (LCol. James Kelly), and 88th New York (LCol. Patrick Kelly) Regiments, along with the somewhat "Puritan" 29th Massachusetts (LCol. Joseph H. Barnes).
Together, the Brigade had a superb record from Bull Run to Appomattox, though there were few of the original members left after the glorious and brave, but deadly charges they made both here at Antietam and the following December against the enemy behind a stone wall at Fredricksburg.
On September 17, 1862 they were the leading regiments in the Division's attack on the entrenched Confederates down in the Sunken Road. The following account of the attack was excerpted from General Meagher's official after-battle report.
[full text report]
...following the lead of Major-General Richardson, who conducted the brigade to the field of battle, under cover of the rising ground and depressions which intervened between us and the enemy, we arrived at a cornfield, where Major-General Richardson ordered that everything but cartouch-boxes should be thrown off. The men of the Irish Brigade instantly obeyed this order with a heartiness and enthusiasm which it was rare to expect from men who had been wearied and worn by the unremitting labors of a nine months' campaign.
Deploying from column into line of battle on the edge of this cornfield, they marched through it steadily and displayed themselves in admirable regularity ... the enemy's column, with their battle-flag advanced and deftantly flying in front, was at this time within 300 paces of our line. A clover field of about two acres interposed. Then came the plowed field in which this column of the enemy was drawn up, and from which from their double front they had delivered and sustained a fire before which Sedgwick's forces on the right and French's on the left were reported at the time momentarily to have given way.
The fact is, owing to some reason which as yet has not been explained, the Irish Brigade had to occupy and hold a gap in the line of the Union army, which the enemy perceiving had flung a formidable column to break through, and so take the two divisions last named on their flank and rear. This movement was suddenly checked by the impetuous advance of the Irish Brigade, which in a great measure filling up the gap through which the rebel column was descending to the rear of the Federal lines, drew up in line of battle within 50 paces of the enemy, the Sixty-ninth and Twenty-ninth being on the right of the line, and the Sixty-third and Eighty-eighth Regiments on the left. On coming into this close and fatal contact with the enemy, the officers and men of the brigade waved their swords and hats and gave the heartiest cheers for their general, George B. McClellan, and the Army of the Potomac. Never were men in higher spirits. Never did men with such alacrity and generosity of heart press forward and encounter the perils of the battle-field
My orders were, that, after the first and second volleys delivered in line of battle by the brigade, the brigade should charge with fixed bayonets on the enemy. Seated on my horse, close to the Sixty-ninth Regiment, I permitted them to deliver their five or six volleys, and then personally ordered them to charge upon the rebel columns, while at the very same moment I ordered Captain Miller, assistant adjutant-general of the brigade, and Lieutenant Gosson, first aide on my staff, to bring up the Eighty-eighth and Sixty-third immediately to the charge.
It was my design, under the general orders I received, to push the enemy on both their fronts as they displayed themselves to us, and, relying on the impetuosity and recklessness of Irish soldiers in a charge, felt confident that before such a charge the rebel column would give way and be dispersed.
Advancing on the right and left obliquely from the center, the brigade poured in an effective and powerful fire upon the column, which it was their special duty to dislodge. Despite a fire of musketry, which literally cut lanes through our approaching line, the brigade advanced under my personal command within 30 paces of the enemy, and at this point, Lieut. Col. James Kelly having been shot through the face and Capt. Felix Duffy having fallen dead in front of his command, the regiment halted.
At the same time Lieutenant-Colonel Fowler and Maj. Richard Bentley, of the Sixty-third, on the left of our line, having been seriously wounded and compelled to retire to the rear, the charge of bayonets I had ordered on the left was arrested, and thus the brigade, instead of advancing and dispersing the column with the bayonet, stood and delivered its fire, persistently and effectually maintaining every inch of the ground they occupied, until Brigadier-General Caldwell, bringing up his brigade, enabled my brigade, after having been reduced to 500 men, to retire to the second line of defense.
Of other transactions on the battle-field in connection with the Irish Brigade I will not presume to speak. My horse having been shot under me as the engagement was about ending, and from the shock which I myself sustained, I was obliged to be carried off the field. It was my good fortune, however, to be able to resume my command early next morning.
[Note: there were newspaper and Army rumors and stories immediately after the battle suggesting that it may have been whiskey that knocked the General from his saddle. Meagher denied that was the case, and nothing was ever actually proven.]
For a more complete picture, see a transcription of the Carman Manuscript as it concerns the Irish Brigade and the Confederate Units opposing in the Sunken Road (from the 29th Massachusetts 140th Reenactment pages).
The Wild Geese, an Irish history project, have published an excellent feature about the Brigade's assault on "Bloody Lane" (scroll down), a story about the 135th Anniversary reenactment of the battle, and an article about the dedication of the new Irish Brigade Monument at Antietam.
You might also like to visit a very nice site about the "Fighting" 69th New York Regiment for more about the regiment and the history of the Irish Brigade.
Also, don't miss the site of the Irish Brigade Association.
For your viewing pleasure, Civil War artist Mort Kunstler has done a magnificent painting on the Brigade at Antietam which can be seen at his Official Website (commercial site).