Soon after the assignment of General Meade to the command of the Army, General Reynolds was directed to take command of the right wing, composed of  the First and Eleventh corps, General Doubleday succeeding to the command of the First Corps, General Rowley to that of the Third Division, and Colonel Biddle, of the One Hundred and Twenty First, of the First Brigade, of which the 142d was part.  Upon arrival of the brigade upon the field, it was formed in line in the open ground, to the left of the wood where General Reynolds fell, and soon became the target of the enemy's batteries in front and right flank.  Its position was subsequently shifted to avoid the fire, but it stubbornly held its ground.  Finally, just previous to the general advance of the enemy along the whole front, from beyond the Millersburg Road on his right, to the Alms House on his left, a part of the brigade was ordered to the support of General Stone's Brigade, which had been hard pressed by infantry.  But at that moment the enemy was descried advancing in double lines, from a wood three-quarters of  a mile to the left and front of the ground where the brigade was posted, and it was immediately wheeled into position to meet it, the One Hundred and Forty-Second holding the right of the line, until joined, a few minutes later, by the order of General Rowley, to fill a gap existing between this and the Iron Brigade, further to the right.  For some time the brigade maintained its position against a vastly superior force.  The enemy not only poured in a rapid fire in front, but moved a body of his troops along the road to the left, and completely flanked the position.  With ranks terribly thinned, the brigade could hold its ground no longer, and the left of the line began to crumble.  The One Hundred and Forty-Second fell back slowly.  The One Hundred and Fifty-First, on its right, held its ground a few minutes longer.  Colonel Biddle, seizing a stand of colors, gallantly rode forward, and the line instinctively about wheeled and followed him.  The horse of Colonel Biddle was shot.  Colonel Cummins, the commander of the 142d, fell mortally wounded.  His horse had been killed a few minutes previously.  Near him fell the Acting Adjutant, Lieutenant Tucker.  The Regiment again fell back slowly towards the Seminary.  Here it joined a mass of men from various brigades and divisions, in some confusion, who were holding and continued to hold the position until the batteries had been withdrawn, and until the enemy, moving along the road south of the Seminary, had completely flanked the position.  As the troops retired through the town, they were subjected to a severe fire from a flanking column, which was sheltered by fences and buildings.
     On reaching the Cemetery, whither it had been ordered, the remnant of the regiment was collected, and less than a hundred were in rank.  About forty, who had become separated from the rest in the retreat, re-joined them before morning.  The appearance of General Sickles, riding into the inclosure where the men were resting, with his staff and corps ensign, was hailed with cheers, as the first assurance that the remainder of the army was not far off.  In reply to a question, the General said pleasantly that his boys were there, and were anxious for a fight.
      In the action of the 2d, the 142d was not involved, but was held in reserve just back of the Cemetery, and Round Top.  On the morning of the 3d, together with the 121st,  the 142d was moved to the left, half a mile, and posted on the right of Stone's Brigade, mid-way between the Cemetery and Round Top.  In the terrible artillery duel, which opened at a little after noon, it was exposed, in open ground, to the full effect of the deadly missiles.  Almost the entire field was in full view from the position it occupied.  The rebel fire was unusually accurate.  Caisson after caisson on the Union side was exploded, and guns were disabled.  But new caissons were speedily brought up, and fresh batteries were hurried forward to take the places of those lost, preserving an unbroken front.  The grand charge of the infantry which followed (Pickett's Charge), struck with its main force to the right of the line where the 142d stood, and consequently it suffered little loss, and easily held its position.  Captain Charles H. Flagg, serving on the staff of General Rowley, was killed, near the close of the day, one of the last officers of the Union army who laid down his life on the Gettysburg field.  The loss to the One Hundred and Forty-Second, in the entire battle for Gettysburg, was fifteen killed, one hundred and twenty-six wounded, and eighty-four missing or prisoners; an aggregate loss of  two hundred and twenty-five.