A station (No. 4) of observation was established in a point of woods south of Yorktown, at the junction of the Hampton and Warwick roads. This station was a mile from the works at Yorktown, and yet nearer the enemy’s work known as the Red Redoubt. Communications hence  by signals were sent to a signal station (No. 2) placed on the saw-mill at General Heintzelman’s headquarters, and were thence reported to headquarters station. Another station of observation (No. 3), in like manner repeating its messages through Station No. 2, at General Heintzelman’s headquarters, was established on the Warwick road, in a piece of woods north of the cleared land in front of Lee’s Mill, and near a small lunette, afterward taken by our forces. The post of observation of the officers here placed extended through a piece of woods southerly to the open ground in front of Wynn’s Mill.
The position of these stations was easily discovered by the enemy. They were held through the siege with much risk to the officers ordered upon them. It was necessary to keep the officers there posted on duty for several days in succession, so that they might well know the localities of the enemy. The stations were hidden from the view of the rebel gunners. The danger was of injury from the fragments of the many shells thrown at the position during the thirty days they were occupied.
A signal flag was displayed in a tree, in sight of the enemy, at Station No. 3. The attempt to remove it was made hazardous by the enemy’s musketry.
These completed the line of stations on the right. The dense woods covering the center and left of the army rendered signaling there impossible except from artificial stations. Soon after the siege had commenced the chief signal officer was directed by the general commanding to cause signal towers to be erected and to be occupied as stations of observation and communication (if that was possible) along the front. It was hoped, also, that by observing from such points of view, and reporting the ranges of the shot and shell, the fire of guns and mortars soon to open on Yorktown .might be accurately directed. These instructions were communicated to Lieut. B. F. Fisher, acting signal officer, commanding the signal detachment on the left of the army, and Lieut. N. Daniels, acting signal officer, commanding that with the center.
The sites for the towers on these portions of the line were at once selected by these officers. Large working parties reported to them, and the work of construction was commenced. On the right of the line, also, the positions for three towers were selected, and the timber for their construction was drawn from the woods and sharpened. Of these towers one (H) was to be on the shore of the bay, near Farinholt’s house. A second (F) was to be on the high bank near the dam crossing Wormley’s Creek. The third (G) on the elevated plain near the Clark house and near Camp Winfield Scott. None of these were, however, completed when the evacuation of Yorktown took place.
A station had been built close to Camp Winfield Scott, in an immense tree. This was sometimes used for purposes of observation. Other stations or perches were now made on trees close to the trenches and batteries of our approaches. From one of these, near Moore’s house, and at a height of about 80 feet from the ground, could be had a distinct and close view of the enemy’s works at Yorktown.
At the center Lieutenant Daniels, acting signal officer, caused to be raised a lofty structure of logs (E) near our picket line in front of Lee’s Mill, and overlooking part of the enemy’s works there placed. This tower was constantly occupied by a detail of signal officers as a station of observation, and whatever facts could thence be noted were reported to General Sumner. It was often visited by other officers, whose duties were aided by the observations here made. This structure was in close range of the enemy’s guns. Though partially hidden by trees,  it might have been demolished by them. They hesitated, however, to fire upon it, curious (as I have since been informed) to learn forwhat it was intended. Along the left of the line the parties commanded by Lieut. B. F. Fisher, acting signal officer, erected four tower stations (A, B, C, D). These stations were occupied, and communicated with each other by signals. The positions commanded views of parts of the enemy’s lines. The reports thence made were sent to General Keyes’ headquarters. The enemy brought a light gun to bear upon one of these towers and sometimes fired upon it, but they were neither able to seriously disturb its occupants nor to interrupt their labors. With this enumeration have been mentioned all the permanent stations established during the siege.
The duties of reconnaissances and communication performed by the officers of the Signal Corps when not occupying these stations have been before referred to. There was no day in the siege but that they could be found in front of the enemy’s lines closely watching his works, and there was in consequence no day but on which some of them were exposed to the dangers of this position. Of the character of the reports made and messages sent by these officers the general commanding had knowledge at the time.
On the 16th of April, 1862, occurred the affair of the Burnt Chimneys, or Lee’s Mill. Mention has already been made by name of the officers particularly engaged at this place. The messages sent by them were sent at very short distances, and I have no reliable information as to their importance. They were useful, perhaps, in conveying intelligence which might if otherwise sent have necessitated the greater exposure of other officers. The observations reported by some of the officers were made from tops of trees they had climbed for the purpose.
In the last days of April the division commanded by General Franklin arrived on transports at Shipping Point. These troops were kept on shipboard for several days, and it was supposed they were to be moved against the enemy at Gloucester. A detachment of 5officers and 12 men, commanded by Lieut. D. E. Castle, Nineteenth Indiana Volunteers, and acting signal officer, was assigned to duty with these forces, and reported to General Franklin, whose headquarters were then on shipboard.
Official Records of the Rebellion: Volume Eleven, Chapter 23, Part 1: Peninsular Campaign: Reports, pp.230-232
web page Rickard, J (19 November 2006), http://www.historyofwar.org/sources/acw/officialrecords/vol011chap023part1/00012_07.html