Do yo have the
Official Military Atlas of the Civil War in your library? It was prepared to accompany the Official Record. If anyone does not have one, I encourage you to do so.
I am not familiar with the Army of the Potomac's topological unit. My examples will be taken from the history of the Army of the Cumberland's ground breaking topological unit.
Army of Tennessee Engineer Camp.
An officer is hand drawing a map & making reproductions via tracing paper.
Detail of General Polk's Map.
This map shows the signal stations between Murfreesboro & Franklin TN.
During the winter & spring of 1863 map makers of the Army of the Cumberland & Army of Tennessee worked to provide their commanders with maps of Middle Tennessee. Both Rosecrans & Bragg were preparing for the spring campaigning season. Vanderbilt University has the original map that General Polk's Corps on the western side of the Shelbville line. The detail above was hand drawn & copied by an Irish civil engineer. Anybody who has ever used tracing paper has made a copy exactly the way the Army of Tennessee's tactical maps were reproduced.
Detail of tactical map Army of the Cumberland
Rosecrans' cavalry concentrated at Rover before advancing on Shelbyville June 23rd 1863.
None of the detailed information shown above is on General Polk's map.
Plate XXXIV of the Official Atlas is a double page spread of five of the Army of the Cumberland's tactical maps drawn under the supervision of Capt. W.E. Merrill. Like so many of the ingenious, entrepreneurial officers in the A of the C, Merill supervised what became the best topographical operation of the CW.
The detail above was what is called a "quick map." It was reproduced by the lithographic printing process. These highly detailed maps were issued with orders for officers to mark corrections & notes on the quick map & return it to Merrill's office. At Stones River NB, there is a map folded to fit the map pocket of an officer's coat tail with notations. Based on these mark one eye ball observations, corrected maps would be consulted at headquarters & orders issued based on the best information available. Needless to say, this detail of the map freshly updated on June 10th 1863 date of the map is of the same terrain as General Polk's map was invaluable on June 23rd 1863 when the Tullahoma Campaign began.
General Roscrans' map of the opening positions June 23rd 1863. Map Official Atlas
This map is roughly 50 X 60 miles. It shows the opening phase of the Tullahoma Campaign. Rosecrans officers would have had copies of this map in their coat tail map pockets. My post it note arrows indicate the 55 mile wide front of the opening day's operations. Needless to say, having such detailed, fresh topographical data gave Rosecrans & Thomas the situational awareness that allowed them to exploit the unexpected break through at Beech Grove (Hoover's Gap).
A very rare surviving example of an Army of the Cumberland Sun Map LOC
On the portentous 4th of July 1863, the Tullahoma Campaign came to its successful end. The Army of Tennessee had been able to escape destruction because of a 500 year weather event. Torrential rain poured down on Middle Tennessee for weeks on end. The Army of the Cumberland paused at the top of Monteagle Mountain. The next weeks would be filled with preparations for crossing the Tennessee River & the advance on Chattanooga. As anyone who has so much as driven between Murfreesboro & Chattanooga TN on I-24 will testify, the route involves some very dramatic ups, downs & winding turns. Needless to say, apart from the single track N&CRR. & its 2,200 foot tunnel through Monteagle, the 1863 roads were barely more than trails. Current, accurate maps were absolutely vital.
The strange looking map above is one of the few surviving examples of a sun map. It was reproduced vial a mechanism invented by the man who created blue prints. What you are looking at is a map made by a copy machine. Something in the neighborhood of 20,000 sun maps were cranked out by A of the C. Many of them were multi colored. The maps were issued with a vial of white ink & a crow quill pen for making notes & corrections. Fresh information could be added to an existing map & accompany orders within 24 hours. At the same time as these revolutionary maps were being cranked out, A of TN officers were still using tracing paper just like my little granddaughters do.
Map prepared exclusively for Sherman & senior commanders. LOC
One of the most eye popping quotes I have ever read was in a message that Capt Merrill sent to General Sherman. The Atlanta Campaign would have to be put off for five days to allow Sgt. Finegan & his motley crew to finish their work before Merrill could begin printing Sherman's map. General Sherman is on record saying that he would never have attempted the Atlanta Campaign without the map above. It is a lithograph. The map was cut into the rectangular fold lines & mounted on linen. If memory serves, only about a dozen of these maps were created. The cavalry version has a different fold. Who knew that the map pocket of a cavalryman was a different dimension?
If you start looking for it, Sgt. Finegan's name is in the legend box of many of the maps produced during Sherman's operations. If you think about it, an NCO getting top billing is unusual. Fortunately, he is the only one 'n' Finegan in the Union Army. It was Finegan who collected a motley crew of informants who provided Merrill with fine details of the topography of North Georgia. He interviewed peddlers, deserters, drovers, land surveyors, literally anybody that might have intimate knowledge of territory that Sherman would traverse during the Atlanta Campaign. It was Finegan's motley crew that provided Sherman with the route he took to outflank the Rocky Face Ridge position. That track was not even on Joe Johnston's map, let alone the fact that it could support a military movement.
This sun map is a detail take from Sherman's map of North Georgia
Sherman was able to issue orders to his subordinate commanders accompanied by sun map detail copies of his command level map. If you ever wondered how Sherman's subordinates were able to interpret his orders & act on them with such alacrity, here is the key. Sherman could order a unit to concentrate at the Trickum P.O. with the knowledge that the road was rough & it would take time for the movement to take place. The officer tasked with the movement would have received his orders & this map in hand move accordingly. Trickum P.O. is to the left of center fold in the middle of the map. Needless to say, this gave both Sherman & his subordinate commanders extraordinary situational awareness.
Detail of Sherman's Map, March to the Sea
No discussion of Sherman's maps is complete without the map detailed above. This is the map Sherman used to plan the March to the Sea. Sherman's orders were very precise. He was tasked with starving out the Army of the Potomac. He also had to plan a route that would supply his army. This detail is interesting because as he approached the coast, agricultural activity petered out. The land of milk & honey was left behind & his army had to live out of their wagons until they made contact with the fleet.
Legend of Sherman's March to the Sea Map
Printed on every county in Georgia, Sherman had the data collected by the 1860 Census. He knew exactly where to send his columns in order to inflict both the maximum damage & collect supplies sufficient to support his army.
Detail showing data on each county.
To my knowledge, there were no tactical copies of this map made. Very few copies of this map were lithographed. It was a ground breaking amalgam of census data & cartography. Nothing like this map had ever been made before. It only takes a moments reflection to realize both how essential it was for Sherman's planning & execution of the March to the Sea.
Salt copy of original map drawn from a balloon.
Photographers still make salt prints from negatives. It was an early method for making photographic prints on paper. Unlike the sun prints cranked out by the A of C's topographers, it is a one at a time process exactly like printing a photo with negative & chemicals today. It beat the heck out of laboriously tracing maps by hand, but it was very slow. The blotchy shadows on this example are, as far as I know, typical of salt prints. As noted, I have attended gallery shows of modern salt print photographs.
Hopefully, this short essay gives you a quick overview of how maps were reproduced during the Civil War. Every sentence could be a paragraph or an entire chapter of a book on the subject. The Army of the Potomac had very competent topographic unit. Perhaps someone will educate us on how that army's map reproduction system worked.
Late in the war CSA cartographers began reproducing quick maps as well. I am not familiar enough with what they did to comment on it. Like so many innovations, apparently CSA quick map reproductions were adopted too late to make any difference in the outcome of the war.
It would be remiss of me if I did not credit General Thomas for his nurturing of the A of the C's topological capabilities. His use of maps was innovative. Thomas' use of maps is a subject worthy of its own thread.