This must of course be accepted as General Thomas's own estimate of the enemy's strength, on which his own action was based. And it should be remembered that military operations must be based upon the information then in possession of the commander, and just criticism must also be based upon his action upon that information, and not upon any afterward obtained.
General Sherman estimated the force left with Thomas ( 1) at about 45,000 (exclusive of the Fourth and Twenty-third Corps, and Smith's corps coming from Missouri), in which he included about 8000 or 10,000 new troops at Nashville, and the same number of civil employees of the quartermaster's department. The Fourth and Twenty- third corps he estimated at 27,000 men, and Smith's at 10,000, and the cavalry in the field at 7700. All this was sufficiently accurate if no account were taken of men unfit for duty or not equipped. But the official returns show that the number of officers and men present for duty equipped amounted to 49,322 in the department, and in the two corps in the field to 24,265, and in the cavalry in the field, to 4800. There were therefore the following discrepancies in Sherman's estimate, due in part to the discharge of men whose terms had expired, as well as to the usual number of men not equipped for duty in the ranks: In the troops in the department, a discrepancy of 8000; in the army corps in the field, 2735; in the cavalry in the field, 2900 ( 2)--a total discrepancy of 13,635. That is to say, Sherman's own estimate was in excess of Thomas's actual strength by a force greater than either of the two army corps he sent back to help Thomas. If he had sent back another large corps,--say the Fourteenth, 13,000 strong, having besides the moral strength due to the fact that it was Thomas's old corps,--the discrepancy in his own estimate would doubtless have been sufficiently overcome, and the line of Duck River at least, if not that of the Tennessee, as Sherman had assured Grant, would have been securely held until A. J. Smith arrived and Thomas could assume the offensive.
Hood's force was ready to invade Tennessee in one compact army, while Thomas then had in the field ready to oppose it a decidedly inferior force, even admitting the lowest estimate made of that hostile army.