Sherman at the end of his memoirs has a chapter on the military lessons of the war. Two of the most prescient listed by him are the impact of the telegraph and railroads on the War:
For the rapid transmission of orders in an army covering a large space of ground, the magnetic telegraph is by far the best, though habitually the paper and pencil, with good mounted orderlies, answer every purpose. I have little faith in the signal-service by flags and torches, though we always used them; because, almost invariably when they were most needed, the view was cut off by intervening trees, or by mists and fogs. There was one notable instance in my experience, when the signal-flags carried a message. of vital importance over the heads of Hood’s army, which had interposed between me and Allatoona, and had broken the telegraph-wires–as recorded in Chapter XIX.; but the value of the magnetic telegraph in war cannot be exaggerated, as was illustrated by the perfect concert of action between the armies in Virginia and Georgia during 1864. Hardly a day intervened when General Grant did not know the exact state of facts with me, more than fifteen hundred miles away as the wires ran. So on the field a thin insulated wire may be run on improvised stakes or from tree to tree for six or more miles in a couple of hours, and I have seen operators so skillful, that by cutting the wire they would receive a message with their tongues from a distant station. As a matter of course, the ordinary commercial wires along the railways form the usual telegraph-lines for an army, and these are easily repaired and extended as the army advances, but each army and wing should have a small party of skilled men to put up the field-wire, and take it down when done. This is far better than the signal-flags and torches. Our commercial telegraph-lines will always supply for war enough skillful operators.
The value of railways is also fully recognized in war quite as much as, if not more so than, in peace. The Atlanta campaign would simply have been impossible without the use of the railroads from Louisville to Nashville–one hundred and eighty-five miles–from Nashville to Chattanooga–one hundred and fifty-one miles–and from Chattanooga to Atlanta–one hundred and thirty-seven miles. Every mile of this “single track” was so delicate, that one man could in a minute have broken or moved a rail, but our trains usually carried along the tools and means to repair such a break. We had, however, to maintain strong guards and garrisons at each important bridge or trestle–the destruction of which would have necessitated time for rebuilding. For the protection of a bridge, one or two log block houses, two stories high, with a piece of ordnance and a small infantry guard, usually sufficed. The block-house had a small parapet and ditch about it, and the roof was made shot proof by earth piled on. These points could usually be reached only by a dash of the enemy’s cavalry, and many of these block houses successfully resisted serious attacks by both cavalry and artillery. The only block-house that was actually captured on the main was the one described near Allatoona. Our trains from Nashville forward were operated under military rules, and ran about ten miles an hour in gangs of four trains of ten cars each. Four such groups of trains daily made one hundred and sixty cars, of ten tons each, carrying sixteen hundred tons, which exceeded the absolute necessity of the army, and allowed for the accidents that were common and inevitable. But, as I have recorded, that single stem of railroad, four hundred and seventy-three miles long, supplied an army of one hundred thousand men and thirty-five thousand animals for the period of one hundred and ninety-six days, viz., from May 1 to November 12, 1864. To have delivered regularly that amount of food and forage by ordinary wagons would have required thirty-six thousand eight hundred wagons of six mules each, allowing each wagon to have hauled two tons twenty miles each day, a simple impossibility in roads such as then existed in that region of country. Therefore, I reiterate that the Atlanta campaign was an impossibility without these railroads; and only then, because we had the men and means to maintain and defend them, in addition to what were necessary to overcome the enemy. Habitually, a passenger-car will carry fifty men with their necessary baggage. Box-cars, and even platform-cars, answer the purpose well enough, but they, should always have rough board-seats. For sick and wounded men, box-cars filled with straw or bushes were usually employed. Personally, I saw but little of the practical working of the railroads, for I only turned back once as far as Resaca; but I had daily reports from the engineer in charge, and officers who came from the rear often explained to me the whole thing, with a description of the wrecked trains all the way from Nashville to Atlanta. I am convinced that the risk to life to the engineers and men on that railroad fully equaled that on the skirmish-line, called for as high an order of courage, and fully equaled it in importance. Still, I doubt if there be any necessity in time of peace to organize a corps specially to work the military railroads in time of war, because in peace these same men gain all the necessary experience, possess all the daring and courage of soldiers, and only need the occasional protection and assistance of the necessary train-guard, which may be composed of the furloughed men coming and going, or of details made from the local garrisons to the rear.
For the transfer of large armies by rail, from one theatre of action to another by the rear–the cases of the transfer of the Eleventh and Twelfth Corps–General Hooker, twenty-three thousand men–from the East to Chattanooga, eleven hundred and ninety-two miles in seven days, in the fall of 1863; and that of the Army of the Ohio–General Schofield, fifteen thousand men–from the valley of the Tennessee to Washington, fourteen hundred miles in eleven days, en route to North Carolina in January, 1865, are the best examples of which I have any knowledge, and reference to these is made in the report of the Secretary of War, Mr. Stanton, dated November 22, 1865.
Sherman of course had served in the Mexican War when both the telegraph and rail lines were in their infancy. His whole life was lived during perhaps the greatest period of rapid technological progress ever witnessed over a similar span of time. From our vantage point the technology of the Civil War seems crude, even primitive. We should never forget that to those living at the time, the technology seemed, and was, cutting edge and credit is due to those who mastered it and used it effectively.