The position of Malvern Hill, nearly 2 miles from the James River, and yet commanding a view of that stream, is perhaps as perfect as could be chosen for combining by the use of signals the operations and the fire of land and naval forces. From the summit of the hill the roads leading to Richmond by the river and passing Turkey Bridge  are overlooked, and even where the roads approaching pass through dense timber the dust raised by moving columns, showing through the tree-tops, indicate to an observer here placed their position. A signal station was now ordered to be established on the roof of a small house at this point.
A station of observation was ordered to be placed on Haxall’s house, whence a long view is had of the river and the roads near it.
Two officers were placed on board the gunboat Aroostook, which lay in sight of the station at Malvern Hill and also of the Haxall’s station. There was one officer (Lieutenant Clum, acting signal officer) on board of the flag-ship Galena, which had now moved up to near Haxall’s from lower down the river. All this time sounds of a general conflict in our rear were increasing. The battles of White Oak Swamp, New Market, and Glendale had opened and were progressing. The commanding general, who, leaving Haxall’s, had ridden toward the front at the first sounds of the cannonade, returned, and went on board the flag-ship to confer with the naval commander. A signal message was sent to him from Malvern Hill, reporting the lines of communication open. Orders were sent to the signal officers on hoard the gunboats to watch the station on Malvern Hill in case they went into action. Soon after this Lieut. W.G. McCreary, One hundred and second Pennsylvania Volunteers, acting signal officer, stationed on a house at Haxall’s, noticed, about 5miles up the river and approaching, clouds of dust, which, as he thought, indicated the movement of a column of the enemy. The fact, mentioned by him to two officers of the general’s staff, attracted no attention.
Watching this movement for some time, during which he was able to form an estimate of the strength of the supposed column and the distance it had advanced, Lieutenant McCreary, acting signal officer, reported the fact by signals to General McClellan, still on board the Galena. An instant reply inquired how far the enemy was distant, and the answer was met by the announcement that the gunboats would move up and shell them.
The Haxall station was ordered to immediately report by signals to the general any further fact of interest that might occur. The gunboats were got under way at once, and signals passed from one to another to “Come on and shell the enemy.” At this time we had strong batteries on Malvern Hill and a considerable force in that vicinity. The plain on top of the hill was crowded with wagons, and the stragglers from the remainder of the army were being here gathered and formed together. There were preparations to meet an attack, but it was not expected immediately.
The enemy’s column moving down the River road came rapidly through the woods to a point within close range and opened on the heights with field artillery. The long lines of dust in the woods and beyond them marked the positions of their infantry. The contest was rapid and decisive. With the first of the enemy’s shell the hill was cleared as if by magic of wagons and of stragglers, which went down the hill together, and rapidly on to Haxall’s by hundreds. Our batteries on the hill came promptly into position and opened in reply, while the great guns of the fleet threw in their shells fairly among the enemy. Almost as soon as the gunboats had left Haxall’s Station the signal station on Malvern Hill had come in view to the signal officers stationed on the mast-tops, and the signal messages from the field, “Fire one mile to the right,” “Good shot,” “Fire low and into the  woods near the shore,” &c., were reported to the gunners in ‘a few minutes aftertheir broadsides were opened. The gunboats continued their fire for some time after the land batteries had ceased, and until the enemy’s columns, repulsed and scattered, were out of range and hidden from view.
With the first lull of the firing came inquiries by signals from General McClellan as to the progress of the battle still raging with other parts of the army. The reply from General Porter brought the commanding general quickly on shore and on the field, which he reached after night-fall. Messages went to and fro between the field and the gunboats until after dark, when the vessels moved down the river. At the beginning of the action the signal flag stationed and working on a house on Malvern Hill, directly in front of the enemy’s batteries, seemed to attract their attention, and several shots, some of them passing very close, were thrown at it. No injury was done, however, and the working was not suspended. The number of messages crowded on this station from all Parts of the army was too great to admit that all of them should be sent.
During this action other stations were established communicating from the position of General Porter, after he came upon the field, to where our advanced batteries (under General Griffin, stationed a mile distant, on the Quaker road) were firing on the enemy. Some messages in reference to this firing were thence communicated to General Porter. These field stations were withdrawn at dark. A detail of officers and men was posted at the Malvern Hill station, to be on the alert throughout the night in the case of an emergency, and an officer was sent to one of the gunboats, by the order of General McClellan, to open communication thence that night if it was practicable. The vessel had moved so far down the river that the signals were not visible. The stations at Haxall’s, communicating with the fleet near there, were retained. Mention has been made of the names of officers in my preliminary report. The headquarters camp was this night at Haxall’s Station. The next day was fought the principal battle of Malvern Hill.
Official Records of the Rebellion: Volume Eleven, Chapter 23, Part 1: Peninsular Campaign: Reports, pp.256-258
web page Rickard, J (19 November 2006), http://www.historyofwar.org/sources/acw/officialrecords/vol011chap023part1/00012_28.html