HEADQUARTERS EIGHTEENTH ARMY CORPS,
Near Petersburg, August 6, 1864.

SIR: Yesterday, about 6.30 p.m., the enemy sprung a mine, or countermine, on the left of my line of advanced trenches. I happened to be inspecting the lines at the time, and, with General Ames, had just left the part where the explosion occurred. Seeing it, I ordered my reserves under arms, and notified General Ames to move his reserves to the point where most needed, and inform me, by staff officer sent for the purpose, what was the damage and nature of the attack, if any should be made. The blast of the mine was instantly followed by heavy volleys of musketry and a severe cannonade and shelling from all the enemy's batteries. The latter lasted twenty minutes or half an hour, when it subsided gradually, being replied to with spirit along my whole line. The shelling and cannonading from the opposite side of the Appomattox could not be silenced as promptly as usual, owing to the removal, by orders from headquarters, to transports of the heavy artillery from the ridge on this bank of the river. The field artillery was harnessed, and officers and men throughout the command were prompt to take post when the explosion occurred, and prepared to give the rebels a warm reception had they sallied out. This they did not do, and after the subsidence of the musketry and artillery firing on both sides, about dark, matters assumed their usual appearance, except that I had some batteries put in position during the night, the better to sweep my front, and directed the trench guards to be re-enforced opposite the Crater, which was some thirty yards in my front and near the head of a sap where our parties work at night. I also directed a sharp fire upon the Crater, and other measures to prevent a lodgment being made by the enemy in it.

I beg to call attention to the report of Captain Orwig of the gallantry of Lieut. W. H. Killgore and Private Isaac R. Eaton, Battery E, First Pennsylvania Artillery, and recommend them for promotion. We lost one of the finest officers of this corps, Col. G. A. Stedman, commanding Second Brigade, Ames' division, who was mortally wounded while in company with General Ames reconnoitering the ground and preparing to meet any attempt of the enemy to assault.

I inclose a list of casualties, which I am glad to say is small. Every effort is being made on my part to protect the men in the trenches and reduce the daily loss of life.

I am, sir, respectfully, &c., your obedient servant,

                                                                                    E. O. C. ORD,
                                                                                  Major-General of Volunteers     
                                                                                   

Col. J. W. SHAFFER,
Chief of Staff, Department of Virginia and North Carolina.