The Photographic History of The Civil War: in ten volumes, Thousands of Scenes Photographed 1861-65, with Text by many Special Authorities, Volume 5: Forts and Artillery.
Francis Trevelyan Miller, Ed.

Fourteen batteries of seventy-five guns and forty mortars were established across the Peninsula, the work of constructing emplacements beginning on April 17th and ending on May 3d. During the night of May 3d, the Confederates evacuated Yorktown, and the Federal troops took possession at daylight on the 4th.

The peculiarities of the soil and terrain in the vicinity of the opposing works made the labor of installing the siege-artillery very great. The heavier guns would often sink to the axles in the quicksand, and the rains added to the uncomfortable work. The efforts of the strongest and most willing of the horses with the heavy materiel frequently did not avail to extricate the guns from the mud, and it became necessary to haul them by hand, the cannoneers working knee-deep in mud and water. The First Connecticut Heavy Artillery and the Fifth New York Heavy Artillery excelled in extraordinary perseverance, alacrity, and cheerfulness.

The effect of the delay to the Army of the Potomac was to enable the Confederates to gain strength daily in preparation for the coming campaign. All the batteries of the Union line, with the exception of two, were fully ready to open fire when the Confederates evacuated their positions, and these two batteries would have been ready in six hours more. Circumstances were such, however, that fire was actually opened from only one battery, which was armed with two 200-pounder and five 100-pounder Parrott rifled guns.

The ease with which these heavy guns were worked and the accuracy of their fire on the Confederate works, as afterward ascertained, were such as to lead to the belief that the Confederates would have suffered greatly if they had remained in the works after the bombardment was opened. The desired result, however, had been achieved. The Union army had been delayed a month, and precious time had been gained for General Lee to strengthen the defenses of Richmond while Johnston held off his formidable antagonist.