Carleton's foresight had shown him that, in this campaign, an assistant for himself would be absolutely necessary; for, in one respect, Grant's advance was unique. Instead of, as heretofore, the Union army's having its rear in close contact with the North, and all the lines and methods of communication being open, the soldiers and the correspondents were to advance into the Wilderness, and cut themselves off from the railway, the telegraph, and even the ordinary means of communication by horse, wheel, and boat. Carleton, at short notice to the young man, chose for his assistant his nephew, Edmund Carleton, now a veteran surgeon and physician in New York, but then in the freshness and fullness of youth, health, and strength. Alert and vigorous, fertile in resource, courageous and persevering, young Carleton became the fleet messenger of the great war correspondent. He assisted to gather news, and soon learned the art of winning the soldier's heart, and of extracting, from officers and privates, scraps and items of intelligence. Even as the hunter becomes expert in noting and interpreting signs in air and on earth which yield him spoil, so young Carleton, trained by his uncle, quickly learned how to secure news, and to make a "beat." He kept himself well supplied to the extent of his ability with tobacco,--always welcome to the veterans, for which some "would almost sell their souls;" and with newspapers, for which officers would often give what was worth more than gold,--items of information, from which letters could be distilled, and on which prophecies could be based. Very appropriately, Carleton dedicates his fourth book on the war, "Freedom Triumphant," to his fleet messenger. Carleton's first letter in the last long campaign is dated May 4, 1864, from Brandy Station. There four corps were assembled: the Second, Hancock's; the Fifth, Warren's; the Sixth, Sedgwick's; the Ninth, Burnside's. With Sheridan's riders, these made a great city of tents. The cavalry was not the cavalry of Scott's day, but was in its potency a new arm of the service. From this time forth, the Confederate authorities, by neglecting this arm of their service, furnished one chief cause of final failure, while those in Washington steadily increased in generous recognition of the power of union of man and horse. In equal ability of brute and rider to endure fatigue, the Union cavalryman under Sheridan was a veritable centaur.