BATTLE OF MECHANICSVILLE.
About 4 p. m. on the 26th of June a message from Lieutenant Fisher, acting signal officer, then at Hogan’s house, north of the Chickahominy, announced that the enemy was moving down the north side of the Chickahominy; that there would be a battle at Mechanicsville, and that all the troops then on the north side had been ordered to be ready to cross to the south of the Chickahominy. Lieutenant Fisher was about to leave, with the officers collected from the different signal stations near him, for the point at which the battle was expected. Very soon after a message from General Reynolds announced that with the troops under  his command he had fallen back to a predetermined position near Beaver Dam. At almost the same time at which this message was received the roar of the battle at Mechanicsville made it evident it had commenced.
At the commencement of this battle Lieutenant Fisher distributed his officers as follows, viz: Lieutenant Beckett, acting signal officer, with a battery on the right of our line, about 100 yards from a prominent house on the field: Lieutenant Horner, acting signal officer, with the extreme right; Lieutenant Wiggins, acting signal officer, with the reserve. Lieutenant Fisher, with Lieutenant Birney, took post on the roof of the house mentioned, and at which a battery was stationed from these positions, which were occupied as points of observation, the officers were able, by the aid of their glasses, to obtain information which could not otherwise have readily been given. Their reports were made to the different commanders near whom they were serving. Signals were not used upon the field of battle. The fire upon the stations occupied by the officers upon this field was quite severe. The fire of artillery continued until about 9 o’clock at night, and when it closed our troops everywhere had held their positions. During this action one officer had been left at the Hogan station, communicating with the station on Golding’s farm. It was presumed that this station was constantly watched by the enemy.
There is always a possibility that the key to signal communication may be by accident or betrayal in the possession of the enemy. It is customary for this reason to disguise true messages, and to send with an especial signal messages intended to deceive. On this night, as soon as the firing had ceased, the chief signal officer instructed the Hogan station to send, in plain view of the enemy, the message, “The five divisions have arrived.” As our forces intended to leave the position, this message, if it could by any accident be interpreted by the enemy, would lead them to believe that we proposed to hold it. No other messages were sent this night.
The field telegraph train, which had arrived from the south side of the Chickahominy on the morning of this day, had been ordered to be extended from General Porter’s headquarters, which later in the day during the battle was the position of General McClellan, to a point near Old Cold Harbor. The wire had been reeled out accordingly. It had fallen again among new troops, who investigated its composition by cutting it, and the officer going to Cold Harbor had been warned that the enemy were approaching that position and that it would not be held by our troops. The line was not working. Under these circumstances the wire was now ordered to be reeled up and the train to recross the river. At about 10 o’clock the officers and men collected from the field of battle were gathered at Hogan’s station, and arrangements were made for them to take part in the battle of the following day. It was the impression at this time that a great battle would be fought the next day on the south side of the Chickahominy. Lieutenant Fisher was ordered to return to the signal camp near general headquarters, and to rejoin at daylight, with additional officers, the party on the north side of the Chickahominy, to serve with General Porter. The remainder of the party (with the exception of four officers detached to General Hooker) fit for duty was ordered to be at the station at Golding’s farm, equipped, and there to await orders to move with the forces on the south side of the river. The officer in charge of the wagons of the signal detachment was ordered to be ready to strike camp at any time and to accompany the movement of general head-quarters.
Official Records of the Rebellion: Volume Eleven, Chapter 23, Part 1: Peninsular Campaign: Reports, pp.249-250
web page Rickard, J (19 November 2006), http://www.historyofwar.org/source/acw/officialrecords/vol011chap023part1/00012_22.html