Various Union Army Corps.At Gaines' Mill, Slocum's Division of the Sixth Corps was sent to the support of General Porter, and lost 2,021 out of less than 8,000 present in the hot engagement. It was in front of Fredericksburg May 3, 1863, under General Sedgwick, that the Corps made its most brilliant display of dash and daring. It carried at the point of the bayonet Marye's Heights, the strong position before which there had fallen, gloriously but in vain, nearly 13,000 men the previous December. Most of the Corps was held in reserve at Gettysburg, and its casualties there were slight, but it added again to its laurels at Rappahannock Station. In the battles of the Wilderness and Spotsylvania it encountered its hardest fighting, the percentage of killed of the Fifteenth New Jersey in the latter battle being equaled in only one instance during the whole war. At Cold Harbor it suffered heavily again, and the appearance of two of its divisions at Fort Stevens checked Early's advance on Washington. It pursued Early up the Shenandoah, and fought at Opequon and Cedar Creek. In the final assault on Petersburg it played an important part. It was no less prominent in its final appearance at the Grand Review in Washington.