EVACUATION OF YORKTOWN.
By the first days of May our approaches were nearly completed, the siege and mortar batteries were in position, and the day was reported fixed on which they were to open fire. Lieutenant Neel states in his report that two days previous to the evacuation of Yorktown and the main line of works—that is, on the morning of May 2, 1862—Lieutenant Herzog, acting signal officer, and himself reported to General Smith, commanding near Lee’s Mill, the evacuation of the enemy’s main works at that place. I am not informed that this message was sent to general headquarters.
On the night of Nay 2 the unusual silence of the enemy so attracted the attention of the general commanding that in a message ordered to the fleet that night he mentioned that this silence might indicate an evacuation or a sortie, and asked that a gunboat be sent to draw the enemy’s fire. The gunboat Marblehead moved up the river near the batteries, and, firing upon them, drew a number of shots in reply.
On the morning of the 3d of May a signal message was received from Lieut. A. B. Jerome, First New Jersey Volunteers and acting signal  officer on Station No. 3, near Wynn’s Mill, that the enemy were destroying their barracks. This was not supposed to have particular bearing upon an evacuation. On the same afternoon the enemy’s fire opened as usual about sundown, and increased in rapidity after nightfall, until at midnight the roar of artillery was almost incessant. Shot and shell were thrown in all directions, as though fired at random, and with ranges which had rarely been reached before.
Signals with torches were prohibited at Station No. 2 by the general there commanding for fear of drawing the enemy’s fire. The signals made from stations at the front (Nos. 3 and 4) were therefore not answered, and no messages were received. About midnight a conflagration was observed in Yorktown. About 2 a. m. on the 4th the firing ceased, and between that hour and daylight our troops entered the works. Soon after daylight a message was received from Moore’s house, announcing, “Our flag flies over Yorktown.”
The claim is made by the signal officers stationed at the towers (C and E) on the center and left of our lines that the first positive information of the evacuation of the works in front of them was given by them to Generals Sumner and Keyes, with whom they were respectively serving. This report is said to have been made from the tower near Wynn’s Mill at 4.30a. m., and from the tower in front of General Keyes at daylight.
On both the center and the left signal officers went into the works with the first troops that occupied them, and, signaling back reports, gave positive assurance of the absence of the enemy. About 7 a. m. a message from the general commanding announced to the fleet the evacuation of Yorktown.
Lieut. T. R. Clark, acting signal officer with the fleet, on board the Marblehead, had previously, at 5.30 a. m., observed the evacuation from that vessel, and had at that time signaled the report to the flagship.
The fleet at once moved from its anchorage, and occupied the channel between Yorktown and Gloucester.
Upon thefirst announcement of the retreat of the enemy a party under command of Lieut. H. L. Johnson, Fifth Connecticut Volunteers, and acting signal officer, had been sent to Yorktown to establish a signal station in that place, and to send officers to open communication across the river to Gloucester as soon as that place could be safely entered. The officer detailed for this purpose was fairly on his way across the river in a skiff to occupy Gloucester before the enemy had abandoned that position. He was recalled to save him from capture.
As the fleet moved up the enemy hastily abandoned that point, and a signal officer landed with the advance of our troops who occupied it. By 10 a. m. stations had been established (and were working) at Farinholt’s house, Yorktown, Gloucester, and on the fleet, the stations at Gloucester and on the fleet communicating to headquarters through the station on Farinholt’s house.
Communication with the fleet had not been suspended during the movement of the vessels from the anchorage to Yorktown. The messages transmitted this morning were numerous and important. The general commanding received at Camp Winfield Scott reports from Gloucester and Yorktown and from the senior naval officer (on board the flag-ship, some miles distant and out of sight) frequent statements of the position of the fleet; of reconnaissances made up the river and as far as West Point by steamers ordered on that duty; of captures made,  and of the naval plans and orders. In return, he communicated his own wishes (to which he had immediate response) and his plans for the movement of the combined fleet and army.
Among other messages thus telegraphed was one from the general- in-chief, announcing his intention to move up the river that day the transports with the troops under General Franklin, and asking a convoy of war vessels; one relating to the reported embarkation of the enemy at a wharf beyond Williamsburg (which embarkation it was desired to prevent), and one to save the railroad bridge across the Pamunkey River, which the fleet proposed to destroy.
The reports from the fleet showed that the river was without obstruction as far as the White House, that the white flag was flying at severa1 points on its banks and at West Point, and that no troops were there visible. The wharf beyond Williamsburg was reported as destroyed by fire and as yet burning. One or two large vessels were found on the stocks at West Point.
The signal stations on the right of the army, other than those above mentioned, were this day abandoned, and the parties were concentrated to accompany the advance of the army. Late in the afternoon the sound of cannon announced that the advance guard of the army had overtaken the enemy and commenced the battle of Williamsburg.
Official Records of the Rebellion: Volume Eleven, Chapter 23, Part 1: Peninsular Campaign: Reports, pp.232-234
web page Rickard, J (19 November 2006), http://www.historyofwar.org/source/acw/officialrecords/vol011chap023part1/00012_08.html