Brigadier-General John A. RAWLINS, Chief of Staff to General GRANT, Chattanooga.
GENERAL: For the first time, I am now at leisure to make an official record of events with which the troops under my command have been connected daring the eventful campaign which has just closed. Dating the month of September last, the Fifteenth Army Corps, which I had the honor to command, lay in camps along the Big Black, about twenty miles east of Vicksburg, Mississippi. It consisted of four divisions:
The First, commanded by Brigadier-General P. J. Osterhaus, was composed of two brigades, led by Brigadier-General C. R. Woods and Colonel J. A. Williamson (of the Fourth Iowa).
The Second, commanded by Brigadier-General Morgan L. Smith, was composed of two brigades, led by Brigadier-Generals Giles A. Smith and J. A. J. Lightburn.
The Third, commanded by Brigadier-General J. M. Tuttle, was composed of three brigades, led by Brigadier-Generals J. A. Mower and R. P. Buckland, and Colonel J. J. Wood (of the Twelfth Iowa).
The Fourth, commanded by Brigadier-General Hugh Ewing, was composed of three brigades, led by Brigadier-General J. M. Corse, Colonel Loomis (Twenty-sixth Illinois), and Colonel J. R. Cockerill (of the Seventieth Ohio).
On the 22d day of September I received a telegraphic dispatch from General Grant, then at Vicksburg, commanding the Department of the Tennessee, requiring me to detach one of my divisions to march to Vicksburg, there to embark for Memphis, where it was to form a part of an army to be sent to Chattanooga, to resnforce General Rosecrans. I designated the First Division, and at 4 r. as. the same day it marched for Vicksburg, and embarked the neat day.
On the 23d of September I was summoned to Vicksburg by the general commanding, who showed me several dispatches from the general-in- chief, which led him to suppose he would have to send me and my whole corps to Memphis and eastward, and I was instructed to prepare for such orders. It was explained to me that, in consequence of the low stage of water in the Mississippi, boats had arrived irregularly, and had brought dispatches that seemed to conflict in their meaning, and that General John E. Smith's division (of General McPherson's corps) had been ordered up to Memphis, and that I should take that division and leave one of my own in its stead, to hold the line of the Big Black. I detailed my third division (General Tuttle) to remain and report to Major- General McPherson, commanding the Seventeenth Corps, at Vicksburg; and that of General John E. Smith, already started for Memphis, was styled the Third Division, Fifteenth Corps, though it still belongs to the Seventeenth Army Corps. This division is also composed of three brigades, commanded by General Matthias, Colonel J. B. Raum (of the Fifty-sixth Illinois), and Colonel J. I. Alexander (of the Fifty-ninth Indiana).